Dissertations / Theses on the topic 'Carbon allocation'

Plants spend a high proportion of their photosynthetically fixed carbon (C) belowground to root biomass, rhizodeposition or to support mycorrhizal fungi in exchange for nutrients while most of this C expenditure is associated with root and hyphal respiration. This thesis aimed to investigate the controls on plants’ C allocation belowground, and what the consequences are for microbial carbon use efficiency (CUE) of soil- vs plant-derived C and for mediating N dynamics. In module system one, four wheat genotypes with variated root traits, biomass and rhizodeposition were grown in pots under two levels of nitrogen (25 and 100 kg N ha-1) and phosphorus (10 and 40 kg P ha-1) fertiliser. Module system two was conducted in a grassland at field condition with two levels of N fertiliser (0 and 100 kg N ha-1) and two levels of clipping intensity (low and high, high applied as double). A continuous and pulse 13CO2 labelling methods was used to quantify rhizodeposition in module system 1 and 2 respectively, and H218O and 15N pool dilution technique to examine CUE and gross N mineralsiation (GNM), respectively. Results showed that plant C allocation to rhizodeposition vs. arbuscular mycorrhizal fungi (AMF) association is mediated by N and P availability. N fertilisation increased AMF association in both module systems, likely because of N-induced P limitation. Although, supporting AMF is C costly, plants sustained supporting AMF with C limitation induced by defoliation in module system 2, resulted in greater root respiration but decreased rhizodeposition. N fertilisation decreased and increased rhizodeposition in module system 1 and 2, respectively, where increased rhizodeposition increased the decomposition, did not affect GNM but contributed to reduced net N mineralisation (NNM) due to microbial N immobilisation at high N. To conclude, plants C allocation belowground is mediated by relative resource availabilities of N, P, and C interacting terrestrial biogeochemistry.

Doctor of Philosophy
Department of Agronomy
Charles W. Rice
Increasing atmospheric CO2 concentrations and other greenhouse gases have been linked to global climate change. Soil organic C (SOC) sequestration in both agricultural and native ecosystems is a plausible option to mitigate increasing atmospheric CO2 in the short term. Laboratory and field studies were conducted to (1) understand the influence of soil water content on the temperature response of SOC mineralization (2) investigate burn and nutrient amendment effects on biogeochemical properties of tallgrass prairie and (3) assess perennial and annual plant management practices on biophysical controls on SOC dynamics. The laboratory study was conducted using soils collected from an agricultural field, currently planted to corn (C4 crop), but previously planted to small grain (C3) crops. The changes in cultivated crops resulted in a δ¹³C isotopic signature that was useful in distinguishing older from younger soil derived CO2-C during SOC mineralization. Soils were incubated at 15, 25 and 35 oC, under soil water potentials of -1, -0.03 and -0.01 MPa. Soil water content influenced the effect of temperature on SOC mineralization. The impact of soil water on temperature effect on SOC mineralization was greater under wetter soil conditions. Both young and older SOC were temperature sensitive, but SOC loss depended on the magnitude of temperature change, soil water content and experiment duration. Microbial biomass was reduced with increasing soil water content. The first field experiment investigated burn and nutrient amendment effects on soil OC in a tallgrass prairie ecosystem. The main plots were burned (B) and unburned (UB) tallgrass prairie and split plots were nutrient amendments (N, P or N+P including controls). Vegetation was significantly altered by burning and nutrient amendment. Treatment effects on either TN or SOC were depth-specific with no impact at the cumulative 0-30 cm depth. The P amendment increased microbial biomass at 0-5 cm which was higher in unburned than burned. However, at 5-15 cm depth N amendment increased microbial biomass which was higher in burned than unburned. In conclusion, soil OC in both burned and unburned tallgrass prairie may have a similar trajectory however; the belowground dynamics of the burned and unburned tallgrass prairie are apparently different. Another field experiment assessed SOC dynamics under perennial and annual plant management practices. The main plots were grain sorghum (Sorghum bicolor) planted in no-tillage (NT) or continuous tillage (CT), and replanted native prairie grass, (Andropogon gerardii) (RP). The spit plots were phosphorus (+P) and control without P (-P). The P amendment was used to repress arbuscular mycorrhizal fungi (AMF), known to influence soil aggregation. The macroaggregate >250 µm, SOC and TN were higher in RP and NT than CT. The relative abundances of AMF and saprophytic fungi were greater with less soil disturbance in RP and NT than in CT. Therefore, less soil disturbance in RP and NT increased AMF and fungal biomasses. The higher relative abundances of AMF and fungi with less soil disturbance increased macroaggregate formation in RP and NT, which resulted in higher SOC sequestration in RP and NT than CT.

Carbon fluxes and allocation pattern, and their relationship with the main environmental and physiological parameters, were studied in an apple orchard for one year (2010). I combined three widely used methods: eddy covariance, soil respiration and biometric measurements, and I applied a measurement protocol allowing a cross-check between C fluxes estimated using different methods. I attributed NPP components to standing biomass increment, detritus cycle and lateral export. The influence of environmental and physiological parameters on NEE, GPP and Reco was analyzed with a multiple regression model approach. I found that both NEP and GPP of the apple orchard were of similar magnitude to those of forests growing in similar climate conditions, while large differences occurred in the allocation pattern and in the fate of produced biomass. Apple production accounted for 49% of annual NPP, organic material (leaves, fine root litter, pruned wood and early fruit drop) contributing to detritus cycle was 46%, and only 5% went to standing biomass increment. The carbon use efficiency (CUE), with an annual average of 0.68 ± 0.10, was higher than the previously suggested constant values of 0.47-0.50. Light and leaf area index had the strongest influence on both NEE and GPP. On a diurnal basis, NEE and GPP reached their peak approximately at noon, while they appeared to be limited by high values of VPD and air temperature in the afternoon. The proposed models can be used to explain and simulate current relations between carbon fluxes and environmental parameters at daily and yearly time scale. On average, the annual NEP balanced the carbon annually exported with the harvested apples. These data support the hypothesis of a minimal or null impact of the apple orchard ecosystem on net C emission to the atmosphere.

Carbon fluxes and allocation pattern, and their relationship with the main environmental and physiological parameters, were studied in an apple orchard for one year (2010). I combined three widely used methods: eddy covariance, soil respiration and biometric measurements, and I applied a measurement protocol allowing a cross-check between C fluxes estimated using different methods. I attributed NPP components to standing biomass increment, detritus cycle and lateral export. The influence of environmental and physiological parameters on NEE, GPP and Reco was analyzed with a multiple regression model approach. I found that both NEP and GPP of the apple orchard were of similar magnitude to those of forests growing in similar climate conditions, while large differences occurred in the allocation pattern and in the fate of produced biomass. Apple production accounted for 49% of annual NPP, organic material (leaves, fine root litter, pruned wood and early fruit drop) contributing to detritus cycle was 46%, and only 5% went to standing biomass increment. The carbon use efficiency (CUE), with an annual average of 0.68 ± 0.10, was higher than the previously suggested constant values of 0.47-0.50. Light and leaf area index had the strongest influence on both NEE and GPP. On a diurnal basis, NEE and GPP reached their peak approximately at noon, while they appeared to be limited by high values of VPD and air temperature in the afternoon. The proposed models can be used to explain and simulate current relations between carbon fluxes and environmental parameters at daily and yearly time scale. On average, the annual NEP balanced the carbon annually exported with the harvested apples. These data support the hypothesis of a minimal or null impact of the apple orchard ecosystem on net C emission to the atmosphere.

Rapid climate change in Arctic regions is of concern due to important feedbacks between the Arctic land surface and the global climate system. A large amount of organic carbon (C) is currently stored in Arctic soils; if decomposition is stimulated under warmer conditions additional release of CO2 could result in an accelerating feedback on global climate. The strength and direction of Arctic C cycle - climate feedbacks will depend on the growth response of vegetation; if plant growth increases some or all of the extra CO2 emissions may be offset. Currently the Arctic is thought to be a small net sink for CO2, the expected balance of terrestrial C sinks and sources in the future is unknown. In this thesis I explore some of the critical unknowns in current understanding of C cycle dynamics in Arctic vegetation. Quantifying gross primary productivity (GPP) over regional scales is complicated by large spatial heterogeneity in plant functional type (PFT) in Arctic vegetation. I use data from five Arctic sites to test the generality of a relationship between leaf area index (LAI) and canopy total foliar nitrogen (TFN). LAI and TFN are key drivers of GPP and are tightly constrained across PFTs in Low Arctic Alaska and Sweden, therefore greatly simplifying the task of up-scaling. I use data from Greenland, Barrow and Svalbard to asses the generality of the LAI-TFN relationship in predicting GPP at higher Arctic latitudes. Arctic ecosystems are unique among biomes in the large relative contribution of bryophytes (mosses, liverworts and hornworts) to plant biomass. The contribution of bryophytes to ecosystem function has been relatively understudied and they are poorly represented in terrestrial C models. I use ground based measurements in Northern Sweden to fill an existing data gap by quantifying CO2 fluxes from bryophytes patches in early spring and summer, and develop a simple model of bryophyte GPP. Using the model I compare bryophyte GPP to that of vascular plants before, during and after the summer growing season, finding that productive bryophyte patches can contribute up to 90 % of modelled annual GPP for typical vascular plant communities at the same site, and that the relative magnitude of bryophyte GPP is greatest in spring whilst the vascular plant canopy is still developing. Understanding how GPP relates to plant growth is important in relating remotely sensed increases in Arctic ‘greenness’ to changes in plant C stocks. I use a 13C pulselabelling techniques to follow the fate of recently fixed C in mixed vascular and bryophyte vegetation, with a focus on quantifying the contribution of bryophytes to ecosystem carbon use efficiency (CUE). I show that bryophytes contribute significantly to GPP in mixed vegetation, and act to increase ecosystem CUE. I highlight the importance of including bryophytes, which do not have roots, in aboveground: belowground partitioning schemes in C models. To further explore C turnover in bryophytes, I use the results of a second 13C labelling experiment to develop a model of C turnover in two contrasting Arctic mosses (Polytrichum piliferum and Sphagnum fuscum). I find significant differences in C turnover between Polytrichum piliferum which respires or translocates about 80 % of GPP, while Sphagnum fuscum respires 60 %. This analysis is the first to explicitly model differences in C partitioning between Arctic bryophyte species. Finally, I discuss the implications of each chapter for our understanding of Arctic C dynamics, and suggest areas for further research.

This thesis focuses on the impact of elevated ozone (O3) and/or nitrogen (N) on semi-natural vegetation, with an emphasis on C-partitioning within and between plant and soil. The project reports several studies allied to the exploration of the impacts of elevated O3 and N employing short-term studies in laboratory-based controlled-environment chambers and solardomes plus long-term studies at free-air O3 fumigation sites in the Swiss Alps and at Keenley Fell, Northumberland, UK. A solardome study indicated that both the grass Dactylis glomerata, and the forb Ranunculus acris exhibited increased senescence, and reduced C-allocation below-ground, when exposed to elevated [O3]. Furthermore, N exacerbated the O3-induced reduction in the root biomass of D. glomerata. This finding led to a mechanistic exploration of C-partitioning in response to short-term (three week) exposure of D. glomerata to a combination of elevated O3 and N inputs in self-built fumigation chambers. Plants were pulse-labelled with 14C, and the fate of the recent photosynthate then traced in nine plant and soil C-pools. The study revealed a reduction in below-ground respiration (incorporating root and soil microbial respiration) in high N treated plants, and a significant antagonistic interaction between O3 and N effects on soil microbial biomass. To relate the findings to below-ground responses in an intact ecosystem, impacts of long-term O3 and N exposure on soil microbial community diversity and C metabolism were investigated in a sub-alpine grassland. Terminal Restriction Fragment Length Polymorphism (T-RFLP) analysis and Community Level Physiological Profiling (CLPP) using 14C labelled root exudate substrates and leaf litter, revealed no effects of O3 and N on the soil bacterial diversity, and limited impacts on C substrate turnover. Moreover, in a long-term study on a traditional UK haymeadow, three years of elevated O3 and N inputs did not result in significant changes in above-ground biomass of any plant functional group. However, a significant O3 x N interaction on below-ground biomass of the sward was observed with reduced root biomass in high [O3] plots. The variation in cover of individual plant species was not explained by either O3 or N when analysed by redundancy analysis (RDA). Overall, this study suggests that N deposition subtly modifies vegetation responses to O3 stress and highlights the potentially significant role played by rising levels of N deposition and O3 as drivers of changes in carbon allocation in the natural environment. Key words: Ozone; nitrogen; carbon allocation; grassland; microbial diversity

1 ABSTRACT Negli oceani attuali, il fitoplancton è principalmente dominato dalle microalghe della linea rossa, con clorofilla a e c, mentre le microalghe della linea verde, con clorofilla a e b, contribuiscono solo in misura minore. Tuttavia, la composizione specifica del fitoplancton è cambiata nel corso dei tempi geologici e le microalghe della linea verde dominavano gli oceani dell’Era Paleozoica, mentre, a partire dall’Era Mesozoica, le alghe della linea rossa diventarono dominanti e diedero origine ai gruppi che sono più importanti negli oceani attuali. Questo cambiamento di dominanza del fitoplancton è stato messo in relazione con la variazione della chimica degli oceani che si è verificata lungo la scala dei tempi geologici. La concentrazione di SO42- negli oceani è aumentata in maniera monotonica dall’Era Paleozoica (~1-10 mmol L-1 SO42-) a oggi (28 mmol L-1 SO42-). Nonostante sia difficile avere informazioni dettagliate sull’abbondanza di NO3- e PO4- negli oceani del passato, ci sono evidenze che anche il rapporto N:P sia cambiato lungo la scala dei tempi geologici, e che gli oceani siano passati dalla limitazione da P a quella da N, dall’Era Paleozoica al presente. Inoltre, il cambiamento dello stato redox degli oceani causato dall’accumulo di O2 rilasciato dalla fotosintesi dal Neo-Proterozoico alla fine del Paleozoico, ha determinato il cambiamento dell’abbondanza di alcuni metalli in tracce, come Fe, Cu, Mn, Mo, Cd e Zn. È stato ipotizzato che la stechiometria elementale media possa essere il link tra il cambiamento della chimica degli oceani e il successo evolutivo delle microalghe della linea rossa. È stato riportato che le microalghe della linea rossa hanno una maggiore richiesta di quegli elementi (S, P, Mn) la cui disponibilità è aumentata quando gli oceani sono diventati più ossidati; il contrario è stato 2 osservato per le microalghe della linea verde, che hanno una maggiore richiesta di nutrienti meno abbondanti in condizioni ossidate (N, Fe, Cu, Zn). Questo suggerirebbe che le alghe della linea rossa siano meglio dotate per far fronte alle condizioni chimiche degli oceani ricchi di ossigeno. Dato che gli organismi della stessa linea evolutiva condividono la stechiometria elementale e i percorsi metabolici, dovrebbero rispondere in maniera simile alla variazione di disponibilità di nutrienti, allocando il C nelle stesse categorie di composti. Le modalità di allocazione del C influiscono sulla biologia delle microalghe attraverso l’impatto che il contenuto energetico esercita sulla palatabilità della cellula e mediante l’effetto della densità cellulare complessiva sulle velocità di affondamento. I differenti composti organici in cui viene allocato il C (proteine, lipidi e carboidrati) non sono equivalenti in termini di densità e di richiesta di energia. Dunque, nella scala dei tempi geologici, le modalità di allocazione del C possono aver avuto un ruolo rilevante sulle traiettorie evolutive del fitoplancton. Può essere ipotizzato che, negli oceani ossigenati e permissivi dal punto di vista ecologico che emersero dall’estinzione di massa Permo-Triassica, le alghe della linea rossa si siano avvantaggiate delle modalità di allocazione del C che ne diminuirono la palatabilità e permisero loro un miglior controllo della galleggiabilità. Lo scopo di questa tesi è valutare l’impatto della variazione della disponibilità dei macro- e micro-nutrienti sulle traiettorie evolutive del fitoplancton. Al fine di perseguire questo scopo, ho pianificato quattro esperimenti per investigare il ruolo potenziale dei seguenti fattori: 3  Disponibilità di NO3-  Rapporto N:P  Disponibilità di SO42-  Disponibilità di Fe, Cu e Mn Il primo esperimento è stato condotto su dieci differenti specie di microalghe appartenenti alle linee evolutive verde e rossa (Amphidinium klebsii, Chlorella marina, Cyclotella meneghiniana, Dunaliella parva, Dunaliella salina, Phaeodactylum tricornutum, Skeletonema marinoi, Tetraselmis suecica, Thalassiosira pseudonana, Thalassiosira weissflogii) e su un cianobatterio (Synechococcus sp.), mentre, per gli altri esperimenti è stato selezionato un numero minore di specie. In parziale disaccordo con l’ipotesi, le modalità di allocazione del C e la loro variazione in risposta ai cambiamenti della disponibilità dei nutrienti (NO3-, SO42- e metalli) erano differenti in alghe che condividono le medesime traiettorie evolutive. Anche gli organismi appartenenti allo stesso genere (Dunaliella parva e Dunaliella salina, Thalassiosira pseudonana e Thalassiosira weissflogii) avevano diverse modalità di allocazione del C in risposta a differenti concentrazioni di NO3-. D’altra parte, le modalità di allocazione del C erano fortemente influenzate dalla taglia cellulare. Quando la biomassa è stata caratterizzata in termini di livello di riduzione complessivo, l’ipotesi è stata verificata, dato che le alghe appartenenti alle due linee evolutive erano marcatamente distinte. Le specie della linea rossa mostravano un livello di riduzione più basso in condizioni che mimano gli oceani attuali, mentre il contrario era vero per le alghe della linea verde. Il maggiore livello di riduzione delle alghe negli oceani attuali si può tradurre in un maggiore contenuto energetico e quindi in 4 una maggiore palatabilità delle cellule per i pascolatori. Questo può aver avuto un ruolo nel favorire l’ascesa alla dominanza delle alghe della linea rossa. Il tasso di crescita della diatomea Thalassiosira pseudonana è stato saturato a un N:P di 13, mentre il tasso di crescita delle alghe della linea verde Dunaliella salina è stato saturato a un N:P di 76. La diatomea non ha cambiato il tasso di assimilazione del NO3- in funzione del rapporto N:P. L’alga verde, invece, ha mostrato una maggiore sensibilità alla disponibilità di NO3- e ha cambiato in maniera apprezzabile il tasso di assimilazione del NO3- in risposta al rapporto N:P. La composizione organica di T. pseudonana è rimasta inalterata in un intervallo di N:P compreso tra 2.6 e 13; per valori di N:P superiori, la diatomea ha modificato la sua composizione e ha aumentato il costo di produzione della biomassa (entrambi sono rimasti costanti quando il rapporto N:P era tra 38 e 152). Dunaliella salina ha cambiato le modalità di allocazione del C in ogni condizione di coltura e ha diminuito il contenuto energetico delle cellule quando è stata coltivata a maggiori rapporti N:P. Dunque, la diatomea ha speso meno energia per produrre la sua biomassa in condizioni di disponibilità di N che mimavano quelle degli oceani moderni; l’alga verde, invece, ha speso meno energia quando è stata cresciuta in condizioni simili al Paleozoico. La disponibilità di SO42- ha influenzato i tassi di crescita delle diatomee P. tricornutum e T. pseudonana e dell’alga verde D. salina: quando queste specie sono state coltivate alla concentrazione di 28 mmol L-1 di SO42- (che 5 mima quella degli oceani attuali), i loro tassi di crescita erano più alti di quando sono state coltivate a una concentrazione di 3 mmol L-1 di SO42- (che mima quella degli oceani del Paleozoico). I tassi di crescita di T. suecica non sono stati interessati dalla disponibilità di SO42-. Nelle alghe verdi, l’efficienza di uso dell’N non è cambiata in funzione della disponibilità di SO42-, mentre quella delle diatomee era maggiore quando la concentrazione di SO42- era alta (28 mmol L-1). La produttività di C delle alghe verdi era più alta a basso SO42- (3 mmol L-1), ma era più bassa ad alto SO42-. Il contrario era vero per le due diatomee. In P. tricornutum e T. pseudonana, il tasso di sintesi delle proteine normalizzato per unità di RNA era considerevolmente maggiore a 28 mmol L-1 di SO42- piuttosto che a 3 mmol L-1 di SO42-. Questo non era vero per le alghe verdi, per le quali non è stato notato nessun cambiamento significativo di questo parametro in funzione delle concentrazioni di SO42-. Le due alghe verdi e le due diatomee usate nei precedenti esperimenti sono state coltivate anche in presenza di differenti concentrazioni di Fe, Cu e Mn. Secondo l’ipotesi che suggerisce che le alghe della linea rossa hanno una maggiore abilità a crescere in ambienti più ossidati, un aumento della disponibilità di Cu e una diminuzione della disponibilità di Fe e Mn dovrebbero favorire queste alghe su quelle della linea verde. I nostri risultati non sembrano confermare pienamente questa ipotesi, dato che le risposte in termini di crescita delle quattro specie alla disponibilità di questi metalli non sono coerentemente correlate alla linea evolutiva. Infatti, la maggior disponibilità di Cu ha stimolato la crescita di P. tricornutum e delle due alghe verdi, ma non di T. pseudonana; la maggior disponibilità di Fe non ha avuto effetto sulle diatomee, ma ha stimolato la crescita di D. salina; il Mn ha stimolato la crescita delle diatomee, ma non quella di D. salina e T. suecica. 6 In conclusione, gli esperimenti riassunti sopra mostrano che:  La diminuzione della disponibilità di NO3- nel corso della storia della terra può aver favorito le alghe della linea rossa  Il declino del rapporto N:P osservato attraverso il Mesozoico può aver avuto un impatto positivo sull’ascesa alla dominanza delle alghe della linea rossa  I cambiamenti secolari dell’abbondanza di SO42- sono compatibili con un ruolo di questo nutriente nell’aver facilitato la predominanza della linea rossa negli oceani moderni  Il cambiamento dello stato redox per se non ha avuto un impatto sull’evoluzione del fitoplancton.
Phytoplankton in the extant oceans is mainly dominated by microalgae of the red lineage, with chlorophyll a and c, whereas microalgae of the green lineage, with chlorophyll a and b, only contribute to a minor extent. However, the species composition of phytoplankton changed over geological time scale and microalgae of the green lineage dominated the oceans of the Paleozoic Era, whereas from the Mesozoic Era the red lineage rose to dominance and gave origin to the groups of algae that dominate the extant oceans. This shift in dominance of the phytoplankton has been put in relation with the change of ocean chemistry that occurred over a geological time scale. The oceanic concentration of SO42- increased monotonically from the Paleozoic Era (~1-10 mmol L-1 SO42-) to the present (28 mmol L-1 SO42-). Although it is difficult to have detailed information about the abundances of NO3- and PO4- in the oceans of the past, there are evidences that also the N:P ratios changed over geological time scale, and the oceans passed from P- to N-limitation, from the Paleozoic Era to date. Moreover, the change of the redox state of the oceans caused by the accumulation of the O2 released by photosynthesis from the Neo-Proterozoic to the end of the Paleozoic, determined a change in the abundance of some trace metals, such as Fe, Cu, Mn, Mo, Cd and Zn. It has been hypothesized that the link between the change of ocean chemistry and the evolutionary success of the microalgae of the red lineage is the average cell elemental stoichiometry. The microalgae of the red lineage have been reported to have higher requirement for those elements (S, P, Mn) whose availability increased when the oceans became more oxidized; the opposite was observed for microalgae of the green lineage, which have higher requirement for nutrients less abundant in oxidized conditions (N, Fe, Cu, Zn). This would suggest that the algae of the red lineage are better equipped to cope with the chemical conditions of oxygenated oceans. Because organisms of the same evolutionary lineage share elemental stoichiometry and biosynthetic pathways, they should respond similarly to the variation of nutrient availability, allocating C to the same pools. The pattern of C allocation affects the biology of microalgae through the impact that the energy content exerts on cell palatability and through the effect of the overall cell density on sinking rates. Different organic pools to which C is allocated (i.e. proteins, lipids and carbohydrates) are not equivalent in terms of density and energy requirement. Therefore, on a geological time scale, the patterns of C allocation may have had a relevant role on the evolutionary trajectories of phytoplankton. It can be hypothesized that, in the oxygenated and ecologically permissive oceans that emerged from the Permo-Triassic mass extintction, the algae of the red lineage took advantage of patterns of C allocation that decreased their palatability and allowed a better buoyancy control. The aim of this thesis is to evaluate the impact of the variation of macro- and micro-nutrients availability on the evolutionary trajectories of phytoplankton. In order to pursue this aim, I designed four experiments to investigate the potential role of the following:  Availability of NO3-;  N:P ratio;  Availability of SO42-;  Availability of Fe, Cu and Mn. The first experiment was conducted on ten different species of microalgae belonging to the green and to the red lineage (Amphidinium klebsii, Chlorella marina, Cyclotella meneghiniana, Dunaliella parva, Dunaliella salina, Phaeodactylum tricornutum, Skeletonema marinoi, Tetraselmis suecica, Thalassiosira pseudonana, Thalassiosira weissflogii) and one cyanobacterium (Synechococcus sp.), whereas, for the other experiments a smaller number of species was selected. In partial disagreement with the hypothesis, the patterns of C allocation and their variation in response to changes in the availability of nutrients (NO3-, SO42- and metals) were different in algae sharing the same evolutionary trajectories. Also organisms belonging to the same genus (i.e. Dunaliella parva and Dunliella salina, Thalassiosira pseudonana and Thalassiosira weissflogii) had different patterns of C allocation in response to different NO3- concentrations. On the other hand, the allocation patterns were strongly affected by the cell size. When biomass was characterized in terms of the overall level of reduction, the hypothesis was verified, since the algae belonging to the two evolutionary lineages were consistently distinct. The species of the red lineage showed a lower level of biomass reduction in conditions mimicking the extant oceans, whereas the opposite was true for algae of the green lineage. The higher level of reduction of the green algae in today’s oceans may also translate to a higher energy content and thus a higher palatability of cells to grazers. This may have played a role in favoring the rise to dominance of the algae of the red lineage. The growth rate of the diatom Thalassiosira pseudonana was saturated at a N:P of 13, whereas, the growth rate of the green alga Dunaliella salina was saturated at a N:P of 76. The diatom did not change the rate of assimilation of NO3- as a function of the N:P ratio. The green alga, instead, showed a greater sensitivity to the availability of NO3- and appreciably changed the rate of NO3-assimilation in response to the N:P ratio. The organic composition of T. pseudonana was unaltered in a range of N:P ratio between 2.6 and 13; above this N:P ratio, the diatom modified its composition and increased the cost of biomass production (both remained constant when the N:P ratio was between 38 and 152). Dunaliella salina changed the pattern of C allocation in each culture condition and tended to decrease the energy content of the cell when cultured at higher N:P ratios. Therefore, the diatom spent less energy to produce its biomass in conditions of N availability mimicking those of extant oceans; the green alga, instead, spent less energy when growth in Paleozoic-like conditions. The availability of SO42- affected the growth rates of the diatoms P. tricornutum and T. pseudonana and of the green alga D. salina: when these species were cultured at a SO42- concentration of 28 mmol L-1 (mimicking that of the extant oceans), their growth rates was higher than when they were cultured at a SO42- concentration of 3 mmol L-1 (mimicking that of the Paleozoic oceans). The growth rates of T. suecica was not affected by the availability of SO42-. In the green algae, The N-use efficiency did not change as a function of SO42- availability, whereas that of the diatoms was higher when SO42- concentration was high (28 mmol L-1). Green algae C productivity was higher at low SO42- (3 mmol L-1), but it was lower a high SO42-. The opposite was true for the two diatoms. In P. tricornutum and T. pseudonana, the rate of protein synthesis normalized on RNA amount was appreciably higher at 28 mmol L-1 SO42- than at 3 and 14 mmol L-1 SO42-. The same was not true for the green algae, for which no significant change of this parameter as a function of SO42- concentrations was detected. The two green algae and the two diatoms used in the previous experiment were also cultured in the presence of different Fe, Cu and Mn concentrations. According to the hypothesis that suggests a higher ability of algae of the red lineage to grow in more oxidized environments, an increased availability of Cu and a decreased availability of Fe and Mn should favor these algae over those of the green lineage. Our results do not appear to fully confirm this hypothesis, as the growth response of the four species to the availability of these metals is not consistently related to the evolutionary lineage. In fact, higher Cu availability stimulates the growth of P. tricornutum and of the two green algae, but not of T. pseudonana; higher Fe availability had no effect on the diatoms, but stimulated growth of D. salina; Mn stimulates diatoms growth, but not that of D. salina and T. suecica. In conclusions, the experiments summarized above show that:  The decrease of NO3- availability in the course of Earth history may have favored the algae of the red lineage  The observed decline of the N:P ratio in the oceans across the Mesozoic may also have had a positive impact on the rise to dominance of the algae of the red lineage.  The secular changes in sulfate are compatible with a role of this nutrient in facilitating the prevalence of the red lineage in modern oceans  The change of redox state per se did not impact the evolution of phytoplankton.

Les processus physiologiques déterminant la productivité forestière and l’allocation du carbone (C) entre les différents organes de l’arbre restent mal connus. La croissance forestière a longtemps été considérée comme limitée par le C, à travers un lien causal entre photosynthèse et croissance (contrôle de la croissance par la source de C). Ce paradigme C-centré est à l’origine des règles gouvernant l’allocation du C dans la plupart des modèles à base de processus (MBP). Cependant, le contrôle de la croissance forestière par la source de C a été remis en cause par un certain nombre d’études mettant en lumière que l’activité des méristèmes est plus sensible aux stress environnementaux (stress hydrique, température basse) que ne l’est l’assimilation du C (contrôle de la croissance par l’activité du puits). De plus, l’effet de la gestion, qui influe fortement sur le fonctionnement de la forêt and sa croissance, n’est pas pris en compte dans la plupart des MBP utilisés pour projeter le futur puits de C terrestre. Notre objectif principal dans cette thèse est d’améliorer notre connaissance des contraintes qui affectent - ou affecteront- la productivité ligneuse des forêts européennes, depuis l’époque actuelle jusqu’à la fin du 21ème siècle. Nous avons abordé cet objectif à travers l’amélioration du modèle CASTANEA, sur la base d’une analyse détaillée des déterminants de la productivité ligneuse annuelle des forêts françaises sur les 30 dernières années. Les espèces étudiées sont Fagus sylvatica, Quercus ilex, Quercus petraea, Quercus robur et Picea abies. Nos résultats suggèrent que la croissance annuelle des espèces étudiées est soumise à un contrôle complexe, impliquant des limitations par la source de C et par l’activité du puits. La variabilité inter-site de la fraction de C allouée à la croissance est principalement expliquée par un déclin lié à l’âge. La croissance annuelle à l’échelle de l’arbre est bien prédite par la taille des individus. Nous avons montré que l’asymétrie de la croissance, i.e., l’avantage des gros arbres dans la compétition pour les ressources, augmente avec la productivité, aux échelles inter-site et inter-annuelle. Sur la base de ces résultats, nous avons développé un nouveau schéma d’allocation du C dans le modèle CASTANEA. Le nouveau modèle a été capable de reproduire de manière satisfaisante la variabilité inter-annuelle et inter-site dans la croissance ligneuse aérienne le long de gradients environnementaux à l’échelle nationale. Le modèle a également été validé en utilisant une méta-analyse de mesure de réserves carbonées et des estimations satellitaires d’indices foliaires. Nos résultats indiquent que la représentation du contrôle de la croissance par l’activité du puits n’affecte pas les prédictions qualitatives de l’évolution de la productivité forestière européenne précédemment obtenues par les MBP C-centrés. Cependant, les MBP C-centrés sous-estiment certainement l’hétérogénéité spatiale des effets du changement climatique.Nous avons enfin utilisé notre nouvelle connaissance des déterminants de la croissance ligneuse annuelle à l’échelle de l’arbre (i.e., les règles empiriques de la compétition) pour calibrer un module simulant la croissance individuelle dans CASTANEA. Le modèle couplé a été utilisé pour évaluer l’effet potentiel de la gestion sur le fonctionnement des forêts et la croissance ligneuse à l’échelle de la France. Nous avons identifié les zones où la gestion pourrait être intensifiée pour réduire l’impact du changement climatique sur la productivité forestière nationale. Environ un quart des forêts françaises en hêtre et chênes tempérés sont en zone de forte vulnérabilité, zone dans laquelle la gestion pourrait donc être utilisée à profit pour limiter l’impact du changement climatique sur la récolte de bois
The processes that underlie forest productivity and C allocation dynamics in trees are still poorly understood. Forest growth has for long been thought to be C limited, through a hypothesized causal link between C supply and growth (source control). This C-centric paradigm underlies most of the C allocation rules formalized in process-based models (PBMs). However, the source limitation of growth has been questioned by several authors, arguing that meristem activities are more sensitive than C assimilation to environmental stresses (e.g., water deficit and low temperatures). Moreover, the effect of management, which strongly affects forest functioning and wood growth, is not accounted for in most of the PBMs used to project the future terrestrial C sink. Our main objective in this thesis was to move forward into our understanding of the constraints that affect - or will affect - the wood productivity in European forests, from present to the end of the 21 st century. We addressed this objective through the improvement of the representation of the forest productivity and C allocation in the CASTANEA PBM, building on a detailed analysis of the key drivers of annual wood productivity in French forests over the last 30 years (the species studied are Fagus sylvatica, Quercus ilex, Quercus petraea, Quercus robur and Picea abies). Our results supported the premise that the annual wood growth of the studied species is under a complex control including both source and sink limitations. The inter-site variability in the fraction of C allocatedto stand wood growth was predominantly driven by an age-related decline. At the tree level, we showed that annual wood growth was well predicted by the individual size. The size-asymmetry of growth, i.e., the advantage of big trees in the competition for resources, increased consistently with the whole stand productivity at both inter-site and inter-annual scales. On the basis of our findings, we developed a new C allocation scheme in the CASTANEA PBM, which integrate a combined source-sink limitation of wood growth. The new calibrated model captured both the inter-annual and inter-site changes in stand wood growth that was observed across national environmental gradients. The model was also successfully evaluated against a meta-analysis of carbohydrate reserve pools in trees and satellite-derived leaf area index estimates. Our results indicated that the representation of the environmental control of sink activity does not affect the qualitative predictions of the future of the European forest productivity previously obtained from source-driven PBMs. However, the current, source-driven generation of PBMs probably underestimates the spatial heterogeneity of the effects of climate change on forest growth that arise from sink limitations.Further, we successfully used our findings regarding the dependences of annual wood growth at tree level (i.e., empirical rules of tree growth competition) to calibrate a module for the simulation of the individual growth of trees in the CASTANEA model. The coupled model was used to assess the potential effects of management on forest functioning and wood growth across France. We identified the areas where management efforts may be concentrated in order to mitigate near-future drought impact on national forest productivity. Around a quarter of the French temperate oak and beech forests are currently in zones of high vulnerability, where management could thus mitigate the influence of climate change on forest yield

Allocation of assimilated carbon amongst plant metabolic processes and tissues is important to understanding ecosystem carbon cycles. Due to the range of spatio-temporal scales and complex process interactions involved, direct measurements of allocation in natural environments are logistically difficult. Modeling approaches provide tools to examine these patterns by integrating finer scale process measurements. One such method is root:shoot balance, where plant growth is limited by either shoot activity (i.e. photosynthesis) or root activity (i.e. water and nutrient uptake). This method shows promise for application on frequently disturbed systems which perturb aboveground biomass and thus create imbalances in root and shoot activities. In this study, root:shoot balance, allometric relationships and phenological patterns were used to model carbon allocation and growth in Florida scrub oaks. The model was tested using ecosystem gas exchange (i.e. eddy covariance) and meteorological data from two independent sites at Merritt Island National Wildlife Refuge, FL which experienced two different types of disturbance events: a prescribed burn in 2006 and wind damage from Hurricane Frances in 2004. The effects of the two disturbance events, which differed greatly in magnitude and impact, were compared to identify similarities and differences in plant allocation response. Model results and process-based sensitivity analysis demonstrated the strong influence of autotrophic respiration on plant growth and allocation processes. Also, fine root dynamics were found to dominate partitioning trends of carbon allocated to growth. Overall, model results aligned well with observed biomass trends, with some discrepancies that suggest fine root turnover to be more dynamic than currently parameterized in the model.; This modeling approach can be extended through the integration with more robust process models, for example, mechanistic photosynthesis, nitrogen uptake and/or dynamic root turnover models.
ID: 029810098; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (M.S.)--University of Central Florida, 2011.; Includes bibliographical references (p. 66-73).
M.S.
Masters
Biology
Sciences

Hybrid physiological models are being increasingly used to assess productivity, carbon sequestration, water and nutrient use and environmental impacts of management decisions. Users include forest managers, politicians, environmental agencies and scientists. However a wider use of these models has been prevented as a result of an incomplete understanding of the mechanisms regulating carbon allocation, nutrient availability in soils and nutrient uptake by trees. On-going innovation in clonal forestry, genetic improvement and vegetation management techniques is also poorly represented in hybrid models. This thesis examines means to represent nutrition and genotype-nutrition interactions in productivity physiological hybrid models. Nutrient limitations and growth differences between genotypes were hypothesized to operate through key physiological processes: photosynthesis, carbon allocation and nutrient internal cycling. In order to accomplish the aims of the study both greenhouse and field experimentation were carried out. In a first experiment, responses of photosynthesis (A) to intercellular CO₂ concentration (Ci) were measured in a fast- and a slow-growing clone of Pinus radiata D. Don cultivated in a greenhouse in a factorial combination of nitrogen and phosphorus supply, and analyzed using the biochemical model of leaf photosynthesis described by Farquhar et al. (1980). There were significant positive linear relationships between the parameters, Vcmax, Jmax, Tp and both foliar nitrogen (Na) and phosphorus (Pa) concentration on an area basis. The study showed that the effects of nitrogen and phosphorus supply on photosynthesis were statistically independent and that the photosynthetic behaviour of the two clones was equivalent. In a similar study, gas exchange and chlorophyll fluorescence were simultaneously measured to determine internal transfer conductance (gm) based on the "constant J method". Transfer conductance may pose significant limitations to photosynthesis which may be differentially affected by nutrition and genotype in Pinus radiata. Values of gm were similar to those of stomatal conductance (gs) and their ratio (gm / gs) was not influenced by nutrient supply or clone being on average (±1 SE) 1.22 ±0.04. Relative mesophyll limitations (LM, 16%) to photosynthesis were marginally greater than those imposed by stomata (LS, 13%), and together smaller than the relative limitations posed to photosynthesis by biochemical processes (LB, 71%). The CO₂ concentration in the intercellular air spaces (Ci) was (±1 SE) 53 ±3 µmol mol-1 lower than in the atmosphere (Ca) while CO₂ concentration in the chloroplasts (Cc) was (±1 SE) 48 ±2 µmol mol-1 less than Ci. Values of LS, LM and LB and CO₂ diffusion gradients posed by gs (Ca-Ci) and gm (Ci-Cc) did not change with nutrient supply or clone. In a third experiment, one-year old Pinus radiata cuttings from four genotypes were cultivated in silica sand with a factorial combination of nitrogen (N0=1.43 and N1=7.14 mM) and phosphorus (P0=0.084 and P1=0.420 mM) supply for 24 months. N supply was enriched with ¹⁵N to 2.5⁰/₀₀ (labelled N) during the first year, then plants transferred to clean sand and cultivated for another year with ¹⁵N at levels close to natural abundance (0.3664899 atom percent ¹⁵N, δ¹⁵N 0.5115 ⁰/₀₀) provided by the source of N in nutrient solution applied during the second year. Recovery of labelled and unlabelled N was used to estimate N remobilization. N remobilization scaled with plant growth, N content and N and P supply. In relative terms, 65% of all stored N was remobilized in the high-nutrient supply regime compared to 42-48% at lower N and P addition rates. Most N remobilization occurred during spring-summer (77%), coincidently with the largest proportion of needle development (80%), indicating that N remobilization was driven by sink-strength. Foliage was by far the main source for internal cycling while roots were the main sink (40%). Clones exhibited differences in N remobilization capacity, but these differences were completely explained by the size of the N pool before remobilization took place, indicating that N remobilization performance was similar among clones. In a fourth study, four clones were cultivated in silica sand with a factorial combination of nitrogen and phosphorus supply for ten months, and patterns of carbon allocation examined using a carbon balance approach. Gross-primary productivity (GPP) scaled mainly with nitrogen but also with phosphorus supply. The fraction of GPP (GPP = ANPP + APR + TBCA) allocated to above-ground components (ANPP) increased with N and P supply at the expense of total-below ground C allocation (TBCA) with no apparent effect on the fraction of GPP partitioned to above-ground plant respiration (APR). Carbon use efficiency (NPP:GPP) scaled with nutrient supply, being 0.42 in the low-nutrient supply regime compared to 0.51 in the high-nutrient supply regime, suggesting that in poor fertility environments a larger proportion of the C budget is respired compared to the net productivity. Fast-growing clones allocated about 2-4% more carbon to above-ground components (ANPP) at the expense of carbon allocated below-ground (TBCA) with no effect on carbon respired above-ground (APR), indicating that faster-growing genotypes allocate more carbon to leaf area which may compound and increase overall GPP over time. The field component of this thesis was conducted in a subset of locations where ENSIS (formerly New Zealand Forest Research Institute) had established trials to test the influence of species, soil disturbance and plant nutrition on sustainability indicators. Plots were small in size (3 m × 3 m) with trees spaced at 0.5 m × 0.5 m (40 000 trees ha-1) with nine measurement trees surrounded by a two-row buffer. All sites were planted in winter 2001 and harvested in spring 2005. The aim of this pilot study was to examine patterns of carbon allocation during the fourth year after planting in control and fertilized mini-plots of Pinus radiata in five sites with contrasting climate and soil conditions in the South Island of New Zealand. The study showed that the fraction of gross-primary productivity allocated belowground increased as the soil C:N ratio increased. However, these results should be interpreted with caution due to the unusual nature of the trial and the reduced number of sites studied. Two existing physiological models were selected for the discussion in this thesis (3-PG, Landsberg and Waring 1997; canopy net carbon exchange model, Whitehead et al. 2002). Potential improvements for the nutritional component of 3-PG comprise: accounting for reductions in carbon use efficiency (NPP:GPP) in poor-fertility environments, adding a preliminary fertility modifier (FN, 0-1) driven by soil C : N ratio and soil N, adding a preliminary relationship between carbon allocation to roots and the soil C : N ratio and representing faster-growing genotypes by increasing their leaf area but not their photosynthetic performance. The canopy net carbon exchange model (NCE) combines the coupled model of leaf photosynthesis - stomatal conductance described by Leuning (1995) with canopy structure and a water balance model to scale carbon assimilation from leaves to canopies. Potential improvements to account for nutrient deficiencies in the leaf model by Leuning (1995), comprise using nutrient ratios to discriminate nitrogen (Na/Pa < 23 mol mol-1) from phosphorus deficiencies (Na/Pa > 23 mol mol-1), adding relationships between photosynthetic model parameters Vcmax and Jmax to Pa, and correcting the estimation of photosynthetic parameters Vcmax and Jmax by accounting for transfer conductance (gm). The canopy net carbon exchange model may be also modified to account for carbon-use efficiency, carbon allocation to roots and genotype in a similar form to that proposed for 3-PG. The results previously outlined provide a preliminary framework to represent tree and soil nutrition in physiological hybrid productivity models.

The aboveground and belowground productivity of forest systems are interlinked through complex feedback loops involving tree, soil and environmental factors. With a predicted significant change in environmental conditions through the enhanced greenhouse effect, it is important to understand the response of forest systems to these new conditions. An increase in atmospheric CO2 is predicted to increase photosynthesis, and therefore whole plant productivity at the individual tree level. However this increase in photosynthesis may result in greater requirements for nutrients, particularly nitrogen (N). In order to acquire any additional available N, trees may respond by increasing their proportional allocation of C belowground to the root system. This study aimed to quantify the belowground C allocation in a mature forest system consisting of a single species on a single site, but with different levels of water and nutrient stress. The belowground carbon dynamics of a range of irrigated and fertilized Pinus radiata stands in Australia were investigated during 1992 and 1993. Belowground carbon allocation was estimated using the model proposed by Raich and Nadelhoffer (1989) where belowground C allocation is the difference between soil respiration and carbon input through litterfall, plus coarse root production and an adjustment for any change in soil and litter layer carbon pools. This model is best described by the equation: Belowground C = Csoilresp ?? Clitterfall + Ccoarseroot+ ???Cforest floor+ ???Csoil Soil respiration, measured using a modified soda lime absorption method either every 2 weeks or every 4 weeks for 2 years, showed a range in daily soil C flux from 137 ?? 785 mgCO2.m-2.h-1. Soil respiration showed seasonal trends with summer highs and winter lows. Limited fine root biomass data could not indicate a strong relationship between measured soil respiration and fine root (>2mm diameter) biomass. Fifty three percent of the variation in soil respiration measurements in irrigated treatments was explained by a linear relationship between soil respiration, and soil temperature at 0.10 m depth and litter moisture content. In non-irrigated treatments, 61% of the variation in soil xix respiration measurements was explained by a linear relationship between soil temperature at 1 cm depth and soil moisture content. Inter-year variation was considerable with annual soil respiration approximately 20% lower in 1993 compared with 1992. Annual soil C flux was calculated by linear interpolation and ranged from 3.4 ?? 11.2 tC ha-1 across the treatments. Soil C pools remained unchanged over 10 years between 1983 and 1993 for all combinations of irrigated and fertilized stands, despite significant aboveground productivity differences over the decade. Measurements of standing litter showed a change between 1991 and 1993 for only 2 out of the 10 treatments. These two treatments had belowground C allocation estimated both with and without an adjustment for a change in standing litter. Annual litterfall C ranged almost four fold from 0.6 ?? 2.2 tC ha-1 between the treatments in 1992 and 1993, and fell within the ranges of measured litterfall over 10 years at the field site. Again inter-year variation was large, with the 1993 litterfall values being approximately 97% greater across all treatments compared with 1992 values. Belowground carbon allocation was calculated using C fluxes measured at the field site, and ranged 3 fold from 4.4 ?????? 12.9 tC ha-1 between the treatments during 1992 and 1993. In 1993 the belowground C allocation was approximately 30% lower across all treatments compared with 1992 calculations. This was due to an approximate 23% reduction in annual soil C flux, a 97% increase in litterfall C and an 18% reduction in coarse root production between 1992 and 1993. The field site was N limited, and differences in belowground C allocation could be shown across irrigated treatments with different N limitations. As N availability increased belowground C allocation was decreased in the irrigated treatments. It was difficult to determine differences in belowground C allocation caused by water stress as the effects of water and N limitation were confounded. An increase in N availability generally indicated an increase in coarse root and litterfall C production, which were reflected in increased aboveground productivity. In high N treatments the coarse root fraction of belowground C allocation comprised approximately 50% of the total belowground C allocation, whereas in the N stressed treatments coarse roots only comprised 20% of the total belowground allocation The mechanistic model BIOMASS was used to estimate annual gross primary productivity (GPP) for the different treatments at the field site. BIOMASS estimated GPPs of between 30-38 tC ha-1 for the different treatments during 1992 and 1993. The measured belowground carbon allocation ranged from 16 ?? 40 % of simulated GPP, with the lower proportion allocated belowground in the irrigated and high fertility stands. Aboveground competition through the absence of thinning also appeared to reduce allocation belowground in non- irrigated stands. A direct trade off between bole and belowground C could not be demonstrated, unless data were separated by year and by the presence or absence of irrigation. Where data were separated in this manner, only three data points defined the reasonably strong, negative relationship between bole and belowground C. The value of this relationship is highly questionable and should be interpreted with caution. Thus a decrease in belowground C allocation may not necessarily indicate a concomitant increase in bole C allocation. Inter-year variation in a number of C pools and fluxes measured at the field site was at least as great as the variation between stands having different water and N limitation. Extrapolation of belowground productivity estimates from a single years data should be undertaken cautiously. The work undertaken in this study indicated that for a given forest stand in a given soil type, an increase in N availability reduced the absolute and relative C allocated belowground. However this decrease in C belowground may not directly translate as an increase in stem growth or increased timber production. Forest productivity in an enhanced greenhouse environment is likely to result in an increased allocation of C belowground due to increased N limitation, unless adequate N is present to support a more active canopy. Further work is required to more fully understand the dynamics of the belowground system in a changing environment. However further research should focus on mature forest systems in order to isolate the impacts of natural ageing changes from perturbation effects on the forest system. This would be best undertaken in long term monitoring sites where a C history of the stand may be available.

The Amazon rain forest plays an important role in regional and global biogeochemical cycling, but the region may undergo an increase in the frequency and severity of drought conditions driven by global climate change, regional deforestation and fire. The effects of this drought on carbon cycling in the Amazon, particularly below-ground, are potentially large but remain poorly understood. This thesis examines the impacts of seasonal and longer-term drought upon ecosystem carbon allocation and cycling at an Amazon rain forest site with a particular focus upon below-ground processes. Measurements are made at three one-hectare forest plots with contrasting soil type and vegetation structure, to observe responses across a range of Amazon primary forest types. A fourth plot is subjected to partial rainfall exclusion to permit measurement of forest responses to a wider range of soil moisture levels than currently exists naturally. An analysis of the number of samples required to accurately quantify important ecosystem carbon stocks and fluxes is used to guide the sampling strategy at the field site. Quantifying root dynamics, in particular, presents methodological challenges. Thus, I critically review existing methods, and develop techniques to accurately measure root standing biomass and production. Subsequently, these techniques are used to record root responses, in terms of standing biomass, production, morphology, turnover and nutrient content, to variation in soil moisture across the four rain forest plots. There is substantial environmental variation in root characteristics. However, several responses remain consistent across plots: root production of biomass, length, and surface area, is lower where soil is dry, while root length and surface area per unit mass show the opposite pattern. The other major component of the below-ground carbon cycle is soil carbon dioxide efflux. I partition this efflux, on each plot, into contributions from organic ground surface litter, roots and soil organic matter, and investigate abiotic and biotic causes for observed differences within and between plots. On average, the percentage contribution of soil organic matter respiration to total soil carbon dioxide efflux declines during the dry season, while root respiration contribution displays the opposite trend. However, spatial patterns in soil respiration are not directly attributable to variation in either soil moisture or temperature. Instead, ground surface organic litter mass and root mass account for 44 % of observed spatial heterogeneity in soil carbon dioxide efflux. Finally, information on below-ground carbon cycling is combined with aboveround data, of canopy dynamics and stem wood production and mortality, to analyze the potential effects of drought upon carbon cycling in an Amazon forest ecosystem. Comparison of the rainfall exclusion plot with a similar, but unmodified, control plot reveals potentially important differences in tree carbon allocation, mortality, reproduction, soil respiration and root dynamics. The apparent net consequence of these changes is that, under drier conditions, the amount of CO2 moving out of the forest and into the atmosphere is diminished. This synthesis of above-ground and below-ground data advances understanding of carbon cycling in rain forests, and provides information which should allow more accurate modelling of the response of the Amazon region to future drought. Additional measurements at other sites, and of other ecosystem carbon fluxes, should further refine modelling predictions.

In the absence of a comprehensive and legally binding international agreement on global emissions reduction, the free of cost allocation of permits has been a political condition of the acceptance of Emissions Trading Schemes (ETSs) in most jurisdictions. As a consequence, up to now, many heavy polluters participating in the ETSs are not paying the full price of carbon. The extent to which pricing carbon affects specific sectors in practice remains unclear in most jurisdictions. In this thesis, I bring together and analyse the economics and legal literature in relation to free allocations. A detailed comparison of the free allocation mechanisms utilised in three ETS systems is then undertaken in order to make recommendations for scheme design rules that will be legally robust and will support the effectiveness of the ETSs, whilst limiting any negative impacts on international trade. Based on a systematic analysis of the available economic data, I observe that carbon leakage rates have been historically overestimated. As a result, governments have been providing free permits to a number of sectors which are not significantly exposed to carbon leakage. Furthermore, the inconsistent eligibility criteria for the free allocation of permits can distort trade between competitors liable under independent schemes. However, such trade distortions may be mitigated by harmonising the free allocation methodologies.The harmonisation process may take place under a linking agreement and should follow a best practice approach, avoiding the eligibility of an excessive number of sectors as carbon leakage exposed. I suggest in this thesis that cumulative criteria of high emission-intensity and high trade-exposure thresholds are recommended, along with the removal of any sole trade-exposure thresholds and sole emissions-intensity thresholds.Differences in the free allocation methodologies can raise legitimate concerns that such allocations can interfere with free trade, thereby invoking the various mechanisms of the World Trade Organization (WTO). I argue that the free allocation of permits is a subsidy according to the definition provided by Article 1.1(a)(1) of the Agreement on Subsidies and Countervailing Measures (SCM Agreement). Subsidies generally represent an unnecessary cost to society and may compromise the fairness of the ETS. I conclude that the European Union Emissions Trading System’s sole emissions-intensity threshold is a de facto specific subsidy, and that it may be actionable if it has adverse effects on the interests of other WTO Members. Furthermore, I argue that the free allocation of permits, based on a trade-exposure threshold, is subject to the notification rule provided by Article XVI, A(1) of the General Agreement on Tariffs and Trade. The European Union has been notably failing to comply with this requirement.

Minimum leaf water potential has been found to be rather constant in coniferous species over a range of environmental conditions and developmental stages. Such a functional homeostasis requires the balanced growth of transpiring foliage, absorbing roots and conductive sapwood, with profound implications for resource allocation, plant allometry and productivity. Although central to the maintenance of plant structure, the process of growth allocation is still poorly understood. The observation of a functional homeostasis in water transport has led to formulate a novel hypothesis of optimal plant growth under hydraulic constraints. The hypothesis has been tested against field and literature data of forest function and growth, choosing Pinus sylvestris as a model coniferous species. The newly developed hypothesis delineates a common framework that seems to explain conveniently changes in growth allocation both over the lifetime of the plant and in response to the environment, helping to explain the variability in forest growth observed at the regional scale as well as the age-related decline in forest productivity. A detailed process model of forest growth (HYDRALL) was developed, centered on the hypothesis of optimal carbon allocation under hydraulic constraints, and applied to the prediction of P. sylvestris growth patterns across Europe. The model was found to predict conveniently several of the growth patterns reported in the literature. Changes in carbon allocation were found to be most important under dry conditions. Information on root hydraulic characteristics under natural conditions is scarce. Part of the research effort was therefore devoted to the development of a new technique for the measurement of the hydraulic resistance of entire root systems of soil-grown plants, a parameter central to the newly developed model.

More than 20 million clonal loblolly pines have been planted throughout the southeastern United States. Fertilizer has been applied to more than 6.5 million hectares of plantations to alleviate deficiencies of nitrogen and phosphorus that limit growth. Because cloning loblolly pine in large numbers has only become possible in the last decade, it is unknown how clones may respond differently to fertilizer application. Growth, growth efficiency, and biomass partitioning responses to fertilizer application were investigated among 25 clones planted in the Virginia Piedmont. Closely related clones varied in their fertilizer stem volume responses, but not enough to be statistically significant (p = 0.11). Clones varied in growth efficiency and partitioning to individual tissues, but clone-by-fertilizer interactions were not observed. Clonal variability was observed in root morphology, and maximum rooting depth showed a significant clone-by-fertilizer interaction.
Clones with rapid growth rates can be selected with a range of other desirable traits. Short-term (i.e. weeks) responses to fertilization are often inconsistent with long-term (i.e. years) responses, but are critical to understanding growth responses. We investigated carbon allocation in two full-sibling clones of loblolly pine under two levels of fertilizer application over four months in a greenhouse. Using monthly harvests of some trees and ecophysiological measurements throughout, we determined carbon allocation on a monthly scale. In response to fertilizer application, both clones reduced allocation belowground and increased allocation to foliage to some extent, increasing whole-canopy photosynthetic capacity. However, these changes in allocation were ephemeral. By the end of the experiment, root-shoot ratios were no longer significantly affected by fertilizer application. Clones had allocation patterns distinct from one another, with one allocating more belowground and the other allocating more to stem mass. While their overall growth responses to fertilizer application were similar, the physiological mechanisms that resulted in these responses were different between clones.
Results of the two studies indicate that while fertilizer responses may not need to be included when testing clones for deployment, knowledge of the fertilizer responses of widely-deployed clones would offer forest managers opportunities to apply clone-specific precision-silvicultural systems to optimize growth rates and manage for a range of products.
Ph. D.

The aim of this study was to gain a comprehensive understanding of the patterns of carbon partitioning, storage and remobilization in Acacia karroo during the juvenile life history stage. Tuber total nonstructural carbohydrate (TNC) concentrations and δ¹³C values were determined in plants from two different stages in the juvenile life history of A. karroo. These were one year after a fire when the plant consisted of numerous leafy shoots or coppices (coppicing stage) and three years after a fire when the plant consisted of one pole like stem (gulliver stage). Gullivers were found to have mean TNC pools of 150g and mean TNC concentrations of 33%. Coppices had mean TNC pools of97g and TNC concentrations of 24%. Both total TNC pools and TNC concentrations in gullivers were significantly higher (p < 0.05) than in coppices. Carbon isotopes were used to determine whether growth was based on carbon reserves as heterotrophic growth shows a distinct enrichment in δ¹³C. The water relations of plants can also influence the δ¹³C values of plant growth. However, there were no significant differences in root size and depth between the stages, indicating that all plants had access to similar water sources. Mean δ¹³C values from the stems of plants in the gulliver stage were significantly enriched(> 1‰) in ¹³C compared to both coppicing plants (p < 0.01) and adults (p < 0.05). The negative δ¹³C values in coppice stems suggest that their growth is not based on stored carbon. The enriched δ¹³C values found in the gulliver stems support the hypothesis that carbon reserves are utilized to achieve fast growth rates in an attempt to escape the fire trap. However, the small magnitude of the differences in δ¹³C between the two stages suggests post-burn regrowth is derived from both current photosynthate and stored carbon.

How carbon (C) is allocated to different plant tissues (leaves, stem, and roots) determines how long C remains in plant biomass and thus remains a central challenge for understanding the global C cycle. We used a diverse set of observations (AmeriFlux eddy covariance tower observations, biomass estimates from tree-ring data, and leaf area index (LAI) measurements) to compare C fluxes, pools, and LAI data with those predicted by a land surface model (LSM), the Community Land Model (CLM4.5). We ran CLM4.5 for nine temperate (including evergreen and deciduous) forests in North America between 1980 and 2013 using four different C allocation schemes:

i. dynamic C allocation scheme (named "D-CLM4.5") with one dynamic allometric parameter, which allocates C to the stem and leaves to vary in time as a function of annual net primary production (NPP);

ii. an alternative dynamic C allocation scheme (named "D-Litton"), where, similar to (i), C allocation is a dynamic function of annual NPP, but unlike (i) includes two dynamic allometric parameters involving allocation to leaves, stem, and coarse roots;

iii.–iv. a fixed C allocation scheme with two variants, one representative of observations in evergreen (named "F-Evergreen") and the other of observations in deciduous forests (named "F-Deciduous").

D-CLM4.5 generally overestimated gross primary production (GPP) and ecosystem respiration, and underestimated net ecosystem exchange (NEE). In D-CLM4.5, initial aboveground biomass in 1980 was largely overestimated (between 10 527 and 12 897 g C m⁻²) for deciduous forests, whereas aboveground biomass accumulation through time (between 1980 and 2011) was highly underestimated (between 1222 and 7557 g C m⁻²) for both evergreen and deciduous sites due to a lower stem turnover rate in the sites than the one used in the model. D-CLM4.5 overestimated LAI in both evergreen and deciduous sites because the leaf C–LAI relationship in the model did not match the observed leaf C–LAI relationship at our sites. Although the four C allocation schemes gave similar results for aggregated C fluxes, they translated to important differences in long-term aboveground biomass accumulation and aboveground NPP. For deciduous forests, D-Litton gave more realistic C_stem ∕ C_leaf ratios and strongly reduced the overestimation of initial aboveground biomass and aboveground NPP for deciduous forests by D-CLM4.5. We identified key structural and parameterization deficits that need refinement to improve the accuracy of LSMs in the near future. These include changing how C is allocated in fixed and dynamic schemes based on data from current forest syntheses and different parameterization of allocation schemes for different forest types.

Our results highlight the utility of using measurements of aboveground biomass to evaluate and constrain the C allocation scheme in LSMs, and suggest that stem turnover is overestimated by CLM4.5 for these AmeriFlux sites. Understanding the controls of turnover will be critical to improving long-term C processes in LSMs.

Différentes approches ont été utilisées pour évaluer les effets de deux formes de nanoparticules de carbone (NPC), nanotubes et graphène, afin de comprendre les mécanismes de la réponse générée par la diatomée benthique d'eau douce Nitzschia palea. Les effets à l'échelle de la communauté ont démontré un impact temporaire sur la croissance du biofilm et une accumulation des NPC dans la matrice extracellulaire. L'application d'une étude transcriptomique a mis en évidence l'importance de l'interaction physique, à l'origine d'altération du frustule, dans la mise en place de cette réponse extracellulaire se traduisant par une surproduction des substances exo-polymériques (EPS). Cette approche a également révélé l'impact des NPC sur l'activité photosynthétique des diatomées et une modification du métabolisme énergétique, suggérant une allocation énergétique en faveur de la production d'EPS. L'étude du protéome extracellulaire a permis d'avoir un premier aperçu de la composition de la matrice extracellulaire, principalement constituée de protéines à caractère hydrophobe. Lors de l'exposition aux NPC, les diatomées semblent produire un système adhésif complexe permettant de renforcer la matrice extracellulaire et d'augmenter la stabilité du biofilm tout en piégeant les NPC. L'exposition des diatomées face au deux formes de NPC induit une réponse présentant une forte similitude notamment pour les plus fortes concentrations testées
Different approaches were used to assess the effect of two forms of carbon-based nanoparticles (CNP) nanotubes and graphene, in order to determine the mechanism of the response generated by the benthic freshwater diatom Nitzschia palea. The effect at the cellular community scale demonstrated a temporary impact on biofilm growth and an accumulation of NPC in the extracellular matrix. The use of transcriptomic study evidenced the role of the physic interaction, causing alteration of the frustule, in the extracellular response leading to an overexcretion of exopolymeric substances (EPS). This approach also revealed the impact of NPC on the photosynthetic activity of diatoms and a modification of the energetic metabolism suggesting an energetic allocation for the EPS production. The study of the extracellular proteome allowed to have a first insight of the extracellular matrix composition, in majority composed of hydrophobic-like proteins. In NPC exposure, diatoms seemed to produce an adhesive system allowing to strengthen the extracellular matrix and increase the biofilm stability while trapping NPC. The exposition of diatoms to the two NPC forms induce a response greatly similar for the highest tested concentration

The tropical forests on the island of Borneo are among of the richest in the world in terms of tree diversity, and their capacity to store a large reservoir of carbon. The Southeast Asian forests are fundamentally different from Neotropical and African forests, with their single-family dominance by dipterocarp trees, and with inherently greater stature and biomass. The carbon productivity and allocation in Asian tropical forests is still poorly quantified, and their responses to environmental drivers are still poorly understood. Almost all recent advances in tropical forest carbon cycling research have occurred in the Neotropics, with very few studies in Asia. The principal aim of this thesis is to quantify the carbon budget of a lowland dipterocarp forest in the Lambir Hills National Park, Miri, Sarawak, Malaysian Borneo. I examined and explored the productivity and carbon cycling processes and their responses to environmental factors across two major and contrasting soil types, in particular the clay and sandy loam soils. I recorded and analysed the Net Primary Productivity (NPP) and respiration for the above- and below-ground components, and observed the responses to seasonal variation and environmental drivers. Total soil respiration was relatively high and contributed a great deal to ecosystem respiration. Variation in soil respiration rates appeared closely related to soil moisture content. I found a strong diurnal cycle in soil respiration. On the basis of the first soil carbon dioxide (CO2) efflux partitioning study undertaken in a tropical forest, the diurnal cycle in total soil respiration appeared to be entirely driven by the diurnal cycle in litter respiration, and in turn litter is strongly controlled by moisture. There was little seasonal variation in allocation of net primary productivity (NPP), but there was evidence showing potential inter-annual variability for several components of NPP. Further, the allocation of NPP showed a strong seasonal shift between the forest plots on clay and sandy loam soils. Combining all the data measured and obtained in this D.Phil. thesis, the overall carbon budget assessed in this lowland dipterocarp forest showed a high level of agreement with other studies in Asia using micrometeorological techniques and the situation appears to be comparable to tropical forests in Amazonia. The key difference is that the aboveground NPP is higher and is the largest component contributing to the overall carbon budget, with relatively higher carbon use efficiency (CUE). The lowland dipterocarp forest in Lambir shows higher allocation in the above-ground NPP, and there were also differences in NPP and its allocation between sandy and clay-rich plots.

L’objectif de cette thèse est de présenter de nouveaux algorithmes de répartition des ressources sous la forme de machines virtuelles (VMs) et fonction de réseau virtuel (VNFs) dans les Clouds et réseaux de diffusion de contenu (CDNs). La thèse comprend deux principales parties: la première se concentre sur la rentabilité des Clouds distribués, et développe ensuite les raisons d’optimiser les coûts ainsi que les émissions de carbone. Cette partie comprend quatre contributions. La première contribution est une étude de l’état de l’art sur la répartition des coûts et des émissions de carbone dans les environnements de clouds distribués. La deuxième contribution propose une méthode d’allocation des ressources, appelée NACER, pour les clouds distribués. La troisième contribution présente une méthode de placement VM efficace en termes de coûts et de carbone (appelée CACEV) pour les clouds distribués verts. Pour obtenir une meilleure performance, la quatrième contribution propose une méthode dynamique de placement VM (D-CACEV) pour les clouds distribués. La deuxième partie propose des algorithmes de placement de VNFs dans les Clouds et réseaux de CDNs pour optimiser les coûts. Cette partie comprend cinq contributions. Une étude de l’état de l’art sur les solutions proposées est le but de la première contribition. La deuxième contribution propose une méthode d’allocation des ressources, appelée CCVP, pour le provisionnement de service réseau dans les clouds et réseaux de ISP. La troisième contribution implémente le résultat de l’algorithme CCVP dans une plateforme réelle. La quatrième contribution considère l’effet de la permutation de VNFs dans les chaîne de services et la cinquième contribution explique le placement de VNFs pour les services à valeur ajoutée dans les CDNs
High energy costs and carbon emissions are two significant problems in distributed computing domain, such as distributed clouds and Content Delivery Networks (CDNs). Resource allocation methods (e.g., in form of Virtual Machine (VM) or Virtual Network Function (VNF) placement algorithms) have a direct effect on cost, carbon emission and Quality of Service (QoS). This thesis includes three related parts. First, it targets the problem of resource allocation (i.e., in the form of network aware VM placement algorithms) for distributed clouds and proposes cost and carbon emission efficient resource allocation algorithms for green distributed clouds. Due to the similarity of the network-aware VM placement problem in distributed clouds with a VNF placement problem, the second part of the thesis, getting experience from the first part, proposes a new cost efficient resource allocation algorithm (i.e., VNF placement) for network service provision in data centers and Internet Service Provider (ISP) network. Finally, the last part of the thesis presents new cost efficient resource allocation algorithms (i.e., VNF placement) for value-added service provisioning in NFV-based CDNs

Three general questions are studied regarding plant carbon allocation strategies. (1) The R* Rule states that the superior competitor in a plant community should exclude all others by minimizing available limiting nutrient concentration below the level needed for survival of its competitors. I asked whether a plant carbon allocation strategy that minimizes the concentration of available limiting nutrient is consistent with Lotka's (1922) conjecture that ecosystems should evolve to maximize total energy flow (primary production). (2) In landscapes such as the Everglades, areas of landscape with higher energy flow (primary production) than the surrounding area also have higher available concentrations of limiting nutrient, rather than lower concentrations, which might be expected from the R* rule. I asked whether this pattern can be explained. (3) I asked how optimal allocation of carbon to plant defense allocation strategies might depend on different conditions of nutrient availability, shading, and herbivory. To address all three questions, I used a model revised from the G'DAY model (Comins and McMurtrie 1993) to study tree allocation of carbon resources between foliage, roots, and defense. With regard to the first question, I found that the allocation strategy that leads to minimum concentration of available nutrients is the same as the strategy for which energy flux to roots, rather than total energy flux, is maximized. Further, I found that the strategy that was competitively dominant was neither the strategy for which total energy flux was maximized, nor that for which available nutrient concentration was minimized. With regard to the second question, I found that, if a patch of vegetation on a landscape is able to capture nutrients from the surrounding landscape, for example, through relatively higher evapotranspiration, it could lead to the opposite of what is expected from the R* rule; that is, available limiting nutrient concentration is maximized when carbon flow to the roots is maximized. With regard to the last question, I found that under high herbivory, the optimal plant strategy for allocation of carbon to defense depends on the available nutrient concentration and amount of radiation to the plant, in agreement with some theoretical predictions.

L’étude du cycle du carbone (C) dans les écosystèmes terrestres est fondamentale afin de comprendre leur rôle dans le cycle du carbone ainsi que les répercussions du changement climatique sur ces écosystèmes. L'objectif général de la thèse qui est de faire un suivi intra-annuel de l’allocation du C au sein de différents écosystème terrestre (forêt et prairie), se place dans ce contexte. Dans un premier temps les efficiences de production de biomasse aérienne (aBPE, rapport entre les quantités de carbone stockées dans la biomasse aérienne et absorbées) sont calculées pour des intervalles de temps réduits, du mois à la semaine selon l’écosystème (forêt et prairie). Dans un second temps, une estimation plus précise de l'allocation du carbone en forêt a été effectuée, en suivant la formation de certains composés structuraux (hémicelluloses et cellulose+lignine). Un possible lien entre la variation de cette allocation selon les conditions climatiques a été étudiée. Les efficiences correspondantes ont également été calculées mensuellement pour avoir une idée plus précise du stockage durable du C dans cet écosystème. Une comparaison avec la prairie a été réalisée en termes d’aBPE afin d'analyser les capacités respectives des 2 écosystèmes à s'adapter aux changements climatiques et à jouer un rôle dans la mitigation des gaz à effet de serre. Dans le cadre de l'Observatoire Pérenne de l'Environnement, deux écosystèmes voisins situés en Meuse (55) ont été instrumentés dans le but de mesurer en continu les échanges de CO2 à l’interface couvert‐atmosphère, ainsi que les conditions micrométéorologiques dans lesquelles ces échanges se produisent. De plus, un suivi régulier du développement des écosystèmes a également été réalisé
The study of the carbon (C) cycle is important in terrestrial ecosystems (forest, grassland) in order to understand their behavior, their role in the C cycle and also the impact of climate change on them. The general study of this thesis which is to monitor the intra-annual allocation of C into different terrestrial ecosystem (forest and grassland), lays within this context. Firstly we calculated aboveground biomass production efficiencies (aBPE, ratio between the quantity of C stored into the aboveground biomass and absorbed) intra-annually, weekly or monthly depending on the ecosystem (grassland and forest respectively). Secondly a more precise assessment of the C allocation in forest was made by analyzing the formation of structural C compounds (hemicelluloses and cellulose + lignins). A possible link between the variability of these allocations and climate was studied. The corresponding efficiencies were then calculated monthly in order to have a better idea of the sustainable C storage in this ecosystem. A comparison with a grassland in term of aBPE was then realized in order to analyze the adaptation capacity of each ecosystem to climate change and to play a role in the mitigation of GHG. Two neighboring ecosystems located in Montiers-sur-Saulx and Osne-le-Val were equipped, as part of the Observatoire Pérenne de l’Environnement (OPE), to measure continuously the CO2 exchange between land cover and atmosphere and the micrometeorological conditions in which these exchanges happen. A regular monitoring of those ecosystems development (biomass, leaves area, senescence) was also made

Mestrado Vinifera EuroMaster - Instituto Superior de Agronomia
Three different pruning methods were used as a model system to challenge fundamental principles in viticulture. Different viticultural and physiological parameters of field grown Chardonnay, Sauvignon blanc, Chenin blanc and Syrah have been quantified, analysed and compared; main focus was on the comparison of ratios between and amongst vegetative and reproductive parameters. Changes in grapevine morphology due to the pruning system as already described in literature could be proofed; number of buds left at winter-pruning is “correlated” with the number of shoots, leaves and bunches formed during the next year. Shoot length, internode length, leaf size and bunch mass are correlated inversely to the number of remaining winter buds. Source:sink relationship has been affected by pruning method due to changes in size and priority of the source and sink organs, which also affected carbon allocation as well as plant biomass development. Impacts on the rachis development have been found, impacting on the % share of berries on a bunch and the ratio rachis length to rachis mass. Alternative pruned vines seemed to have more sanitary problems and appeared not to be adapted for high quality grape production. Almost no parameter or ratio was stable when changing pruning system; indicating the difficulty of imposing absolute numbers and use them as a recipe for decision making in viticulture

Patterns of woody-plant mortality have been linked to global-scale environmental changes, such as extreme drought, heat stress, more frequent and intense fires, and episodic outbreaks of insects and pathogens. Although many studies have focussed on survival and mortality in response to specific physiological stresses, little attention has been paid to the role of genetic heritability of traits and local adaptation in influencing patterns of plant mortality, especially in non-native species. Tamarix spp. is a dominant, non-native riparian tree in western North America that is experiencing dieback in some areas of its range due to episodic herbivory by the recently introduced northern tamarisk leaf beetle (Diorhabda carinulata). We propose that genotype x environment interactions largely underpin current and future patterns of Tamarix mortality. We anticipate that (i) despite its recent introduction, and the potential for significant gene flow, Tamarix in western North America is generally adapted to local environmental conditions across its current range in part due to hybridization of two species; (ii) local adaptation to specific climate, soil and resource availability will yield predictable responses to episodic herbivory; and (iii) the ability to cope with a combination of episodic herbivory and increased aridity associated with climate change will be largely based on functional tradeoffs in resource allocation. This review focusses on the potential heritability of plant carbon allocation patterns in Tamarix, focussing on the relative contribution of acquired carbon to non-structural carbohydrate (NSC) pools versus other sinks as the basis for surviving episodic disturbance. Where high aridity and/or poor edaphic position lead to chronic stress, NSC pools may fall below a minimum threshold because of an imbalance between the supply of carbon and its demand by various sinks. Identifying patterns of local adaptation of traits related to resource allocation will improve forecasting of Tamarix population susceptibility to episodic herbivory.

The Edwards Plateau is the drainage area for the Edwards Aquifer, which provides water to over 2.2 million people. The plateau also provides other ecosystem services, such as wildlife habitat and the sequestration of atmospheric carbon dioxide. The public concern for continued delivery of these ecosystem services is increasing; with private landowners of the plateau region affecting the delivery of these services. A geographic information systems spatial analysis was conducted for Bandera and Kerr counties, with two components being: (1) biophysical and (2) landowner interest. Together these resulted in an overarching map depicting the optimal locations to allocate government assistance to landowners for managing their property to support three ecosystem services: water yield, wildlife habitat, and carbon sequestration.In April 2003, a mail survey of selected landowners was conducted to determine their opinions regarding ecosystem services and cost-share programs (Olenick et al. 2005). In July 2004, a supplemental survey of respondents to the first survey was conducted to follow-up on a few questions answered incorrectly and to focus on landowner opinions regarding cost-share assistance programs and land management activities. Overall, it appeared that five year performance contracts were the most chosen contract type for respondents of all property sizes, earning mid/high annual incomes, and for all length of ownership time periods. Based on our findings, the publicly-funded assistance programs that should be allocated to the optimal ecosystem service locations are five and ten year performance contracts based on property size, length of ownership, and income level categories. The spatial and statistical analysis results were successful, in that optimal locations and types of cost share programs were identified for each ecosystem service in order to prioritize the allocation of limited public resources. The patches of ecosystem target areas within the final target area map can be used as land management demonstration sites to reveal to surrounding landowners the benefits of participating in publicly funded cost-share assistance programs. However, the study has been limited by the generality of the GIS statewide wildlife data.

Les changements globaux affectent la répartition des espèces et le fonctionnement des écosystèmes et sont soumises à des dépérissements massifs. Un des autres processus majeurs de la dynamique forestière est la reproduction sexuée, qui permet aux espèces de persister au fil des générations, notamment grâce à l’adaptation et la migration. Mais il reste de nombreuses incertitudes sur l’effet du climat sur la reproduction des arbres, notamment sur quand et comment sont allouées les ressources au pollen et aux graines. L’objectif principal de cette thèse est d’utiliser une approche basée sur la modélisation des ressources et de la phénologie pour comprendre et prédire l’effet du climat sur la reproduction des arbres forestiers. J’ai d’abord étudié les déterminants impliqués dans les variations spatiales et temporelles de fructification. Puis j’ai quantifié l’allocation des ressources entre les fonctions de croissance et de reproduction à l’aide d’un modèle bayésien hiérarchique. Ce modèle, basé sur des mesures de croissances et de reproduction mâle et femelle sur plusieurs années m’a permis d’identifier des compromis lors de l’initiation florale, et l’importance de la quantité de ressources pour assurer la reproduction. Enfin j’ai développé un modèle mécaniste de reproduction, au sein d’un modèle déjà existant de fonctionnement des forêts (CASTANEA). Le modèle de reproduction, fonctionnant de l’initiation florale jusqu’à la maturation des graines, simule les variations spatiales et temporelles de production de graines. Le modèle a été calibré et validé sur le sapin pectiné au Mont-Ventoux et utilisé pour étudier les effets du changement climatique sur la reproduction
Global changes affect species distribution and ecosystems functioning due to long term climatic trends and extreme climatic events. Forests are notably subject to massive growth decline and even mortality. One of the major processes of forest dynamics is sexual reproduction, but there are still many uncertainties about the effect of climate on trees reproduction, especially on when and how resources are allocated to pollen and seeds. Reproduction also allows species to persist over generations, through adaptation and migration. The main objective of this thesis is to develop an approach based on resource and phenology modelling, in order to understand and predict climate effects on forest trees reproduction. First, I used statistical model to investigate temporal and spatial variation of fruit production. Second, I quantified the allocation of resources between vegetative versus reproductive functions, with a hierarchical Bayesian model and observation of growth, male and female reproduction over several years. Results allowed us to identify trade-off during floral initiation, and highlighted the importance of resources levels to ensure reproduction. Lastly, I developped a process-based model of reproduction and included it in an existing model of forest functioning (CASTANEA). The reproduction model, which runs from flower initiation to seed maturation, simulates spatial and temporal patterns of seed production. The model was calibrated and validated on silver fir on Mont-Ventoux and used to investigate how climate change will impact fruit production

The poor response of some plant species, e.g. wheat, to ammonium nutrition has been attributed to a diversion of carbon allocation from structural material for root extension to functions associated with the assimilation and translocation of ammonium in the root. The aim of this research was to investigate carbon allocation in response to ammonium or nitrate nutrition in wheat, an ammonium intolerant species, and maize, which exhibits ammonium tolerance. Experiments were carried out at 4mM and 12mM nitrogen feeding levels in sand and hydroponic culture respectively. pH of growth media was maintained at 6.0 to 6.5. Measurements made included shoot : root ratios, photosynthetic and root respiratory rates, plant water content, xylem sap analysis, and ¹⁴C and ¹⁵N allocation to soluble and bound nitrogen compounds, and soluble, storage and structural carbohydrates. Stunted root growth occurred in ammonium-fed wheat, which was exacerbated by increasing the NH4 concentration. No difference in growth response was evident between ammonium- and nitrate-fed maize. Photosynthetic rates of ammonium- and nitrate-fed plants within both species were similar but maize showed a 3-fold higher photosynthetic rate than wheat. Root respiration of ammonium- and nitrate-fed wheat was similar, while nitrate-fed maize appeared to have a higher root respiratory rate than ammonium-fed maize. Xylem sap analysis showed that for both species, ammonium-fed plants translocated more amino compounds and more carbon to the shoots than nitrate-fed plants, although maize appeared to have a more rapid translocation-rate than wheat. ¹⁴C allocation to nitrogenous compounds in roots of ammonium-fed plants was greater than that in nitrate-fed counterparts for both species. In wheat this increase appeared to be accommodated by a larger initial diversion of ¹⁴C to the root. In maize, reserve carbon in the root appeared to accommodate this increase. A reduction in ¹⁴C allocation to structural material in ammonium-fed plants compared to nitrate-fed counterparts was not evident in either species. ¹⁵N tracing in maize showed that significantly more nitrogen was taken up by ammonium-fed plants in comparison to nitrate-fed plants. The difference in total N between plants fed ammonium or nitrate was, however, not nearly as pronounced, suggesting that ammonium may be cycled out of the plant again. The response of wheat and maize to ammonium or nitrate nutrition is discussed independently, and suggestions for further research are made.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
The study aimed to calibrate the model 3-PG for Eucalyptus saligna in the region of Guaíba, RS for the following variables diameter at breast height (DBH), total height, wood volume and biomass of stem (branch, bark and wood). The study took place in the region of Guaíba, RS, and clonal plantations of Eucalyptus saligna in various spacings were used. Six different ages were selected along the crop cycle (2nd to 7th year). A forest inventory was carried out in 60 plants per plot for further collection of biomass (three trees fractionated into wood, bark, branches and leaves). The biomass of roots on the medium tree of each plot was measured to a depth of 1 m. Physical and chemical analysis were performed in the samples of soil in layers from 0 to 20 cm, 20 to 40 cm and 40 to 100 cm. Litter deposition was estimated by allocating 4 square wood collectors of 0.5 m². Leaf area was obtained through digital photographs and thus the specific leaf area was estimated. The physiological parameters were measured using the Li-Cor 6400 in six plots, one at each age. Climatic parameters were provided through the Agronomic Experimental Station of the Federal University of Rio Grande do Sul. Allometric and nonlinear equations adjusted for the fraction branch/bark, wood basic density and specific leaf area did not present a good adjustment because there was variability in the data used. Although the estimated values differed from the values observed, the model performance in terms of adjustment exceeded other parameterizations available in the literature. The parameterization and calibration of the model 3-PG were performed satisfactorily meeting all the predictions proposed by the model. The model validation was not statistically accepted, but their estimated data can be used as a source of estimates for the variables studied, demonstrating the potential of its use, however, the need for additional studies to better understanding of this species in this region. The use of the parameters raised by other authors in other regions cannot be used for the region studied.
O trabalho teve como objetivo principal calibrar o modelo 3-PG para Eucalyptus saligna na região de Guaíba, RS para as varáveis diâmetro à altura do peito (DAP), altura total, volume de madeira e biomassa de stem (galho, casca e lenho). O estudo ocorreu na região de Guaíba, RS, sendo utilizados plantios clonais de Eucalyptus saligna, em diversos espaçamentos. Foram selecionadas seis idades ao longo do ciclo de cultivo (2º ao 7º ano). Realizou-se o inventário florestal em 60 plantas por parcela, para posterior coleta da biomassa (três árvores, sendo fracionadas em lenho, casca, galhos e folhas). Na árvore média de cada parcela, mensurou-se a biomassa de raízes até a profundidade de 1 m. Análises físicas e químicas em amostras de solo foram realizadas nas camadas de 0 a 20 cm, 20 a 40 cm e 40 a 100 cm. A deposição de serapilheira foi estimada através da alocação de quatro coletores quadrados de madeira de 0,5 m². A área foliar obteve-se através de fotografias digitais e, a partir destas, estimou-se a área foliar específica. Os parâmetros fisiológicos foram mensurados através do aparelho Li-Cor 6400, em seis parcelas, uma em cada idade. Os parâmetros climáticos foram fornecidos através da Estação Experimental Agronômica da Universidade Federal do Rio Grande do Sul. As equações alométricas e as não-lineares ajustadas para fração galho/casca, densidade básica da madeira e área foliar específica não tiveram bom ajuste, pois há variabilidade nos dados utilizados. Apesar dos valores estimados serem diferentes dos valores observados, o desempenho do modelo, em termos de ajuste, superou outras parametrizações disponíveis na literatura. A parametrização e a calibração do modelo 3-PG foram feitas de modo satisfatório, atendendo todas as predições propostas pelo modelo. A validação do modelo não foi estatisticamente aceita, mas os seus dados estimados podem ser utilizados como fonte de estimativa para as variáveis estudadas, evidenciando o potencial do seu uso, porém, com a necessidade de estudos adicionais para melhor compreensão desta espécie para esta região. O emprego dos parâmetros levantados por outros autores em outras regiões não pode ser utilizada para a região de estudo.

Cette thèse se concentre sur le lien entre la politique sur le changement climatique, le commerce international et la compétitivité pour les industries exposées au commerce à forte intensité énergétique (EITE). En particulier, elle explore la question: la politique climatique peut-elle être conçue de telle sorte que les décideurs politiques puissent dissiper l'inquiétude que toute tentative sérieuse de décarbonation des secteurs EITE conduise à des résultats pervers de délocalisation de la production et des émissions EITE (les « fuites de carbone »)? La thèse aborde cette question en s'appuyant notamment sur les dix années d'expérience de l'UE en matière de tarification du carbone en tant qu'instrument dominant de décarbonation des secteurs EITEs. Ceci est fait en deux étapes. Premièrement, en évaluant empiriquement les solutions politiques existantes de l'UE et en se demandant si les politiques répondent finalement aux critères fondamentaux d'efficacité environnementale, d'efficacité économique et de cohérence des politiques par rapport aux objectifs à long terme de l'atténuation climatique de l'UE. Un certain nombre de lacunes et d'incohérences importantes dans les politiques sont identifiées de cette manière, elles-mêmes intéressantes et pertinentes par rapport aux paramètres politiques actuels. Deuxièmement, cette thèse prend du recul et remet en cause l'idée que le cadre politique global de l'UE- en particulier le rôle dominant du marché du carbone EU ETS - est suffisant pour décarboner ces secteurs à plus long terme
This thesis focuses on the nexus between climate change policy, international trade and competitiveness for energy-intensive trade-exposed industries (EITEs). In particular, it explores the question: Can climate policy be designed such that policy makers can do away with the concern that any serious attempt to decarbonise EITE sectors will lead to perverse results of offshoring of EITE production and emissions – a phenomenon known as “carbon leakage”? The thesis approaches this question by drawingin particular on the 10 years of experience of the EU with carbon pricing as the dominant tool for decarbonising EITE sectors. This is done in two steps. Firstly, by empirically evaluating existing EU policy solutions and asking whether the policies ultimately meet basic criteria for environmental effectiveness, economic efficiency, and policy coherence with respect to the long-term goals of EU climate mitigation. A number of important policy gaps and incoherencies are identified in this way that are of themselves interesting and of relevant to current policy settings. Secondly, this thesis takes a step back and questions and ultimately challenges the idea that the overarching policy framework of the EU– in particular the dominant role of the EU ETS carbon market – is sufficient for decarbonising these sectors in the longer term

Fotossíntese é o processo biofísico pelo qual energia luminosa é transformada em energia química armazenada em compostos de carbono. A taxa fotossintética instantânea possui um forte padrão assintótico em resposta ao incremento da intensidade luminosa, porém quando integramos a fotossíntese em escalas espaciais e temporais maiores, observa-se um padrão linear de resposta entre radiação interceptada e produção. Esta abordagem permitiu o surgimento de modelos baseados nas taxas de conversão de energia radiante em biomassa seca, ou eficiência do uso da luz (ε). Valores publicados para o Eucalyptus estão na faixa de 0,5-2,5 g MJ-1, porém se faz necessário um entendimento mais profundo a respeito da sensibilidade destes valores às flutuações do clima e sua sazonalidade. Para isso, as taxas de crescimento, uso e eficiência do uso da luz foram monitoradas quinzenalmente durante 16 meses em parcelas de 18 clones de Eucalyptus, dos 1,3 aos 2,7 anos de idade. Foram testadas as hipóteses de que a produção de madeira aumentaria em função de incrementos no uso e/ou eficiência de uso da luz, assim como estes valores aumentariam respectivamente com incrementos no índice de área foliar e por uma alocação de carbono para o fuste, respectivamente. Os clones apresentaram uma grande amplitude de produtividade (9,9-22,7 Mg ha-1 ano-1) e arquiteturas de copa, capturando entre 65-95% da radiação incidente. Tais valores resultaram em uma eficiência do uso da luz média de 1,5 g MJ-1, variando entre 0,16-3,14 g MJ-1. Apesar de patamares distintos, os valores de eficiência de uso dos clones oscilaram de maneira similar, de modo que a radiação incidente foi a principal variável afetando a eficiência de uso da luz, estando ε positivamente relacionada a variáveis que expressam períodos de maior disponibilidade hídrica e negativamente relacionado a períodos de menor disponibilidade. Maiores valores de índice de área foliar efetivo (Le) acarretaram em maior interceptação de luz, porém as distintas arquiteturas de copa revelaram diferentes estratégias de captura de luz (0,3 < κ < 0,6). Apesar de uma maior interceptação, não houve correlação significativa com a produtividade, no entanto observou-se uma forte correlação entre eficiência do uso da luz e crescimento em madeira, resultado de uma maior alocação para o fuste. Apesar de evidenciar a relação entre alocação e eficiência, existem outros mecanismos associados às alterações observadas em ε que apenas uma caracterização completa dos fluxos de carbono pode elucidar.
Photosynthesis is the biophysical process by which light energy is converted into chemical energy stored in carbon compounds. The instantaneous photosynthetic rate has a strong asymptotic pattern in response to increases in light intensity, however when we integrate photosynthesis in larger spatial and temporal scales, there is a linear pattern of response between intercepted radiation and production. This approach has allowed the appearance of models based on radiant energy conversion rates into dry biomass, or light use efficiency (ε). Published values for Eucalyptus range from 0.5 to 2.5 g MJ-1, but a deeper understanding of the sensitivity of these values to climate fluctuations and seasonality is necessary. For this reason, wood growth rates, light use and efficiency were monitored every two weeks for 16 months at 18 Eucalyptus clones plots, from 1.3 to 2.7 years of age. Our hypothesis was that wood production would be positively related to light use and efficiency, as well these values would increase respectively with increases in leaf area index and carbon allocation to the stem. Clones showed a wide range of productivity (9.9 to 22.7 Mg ha-1 yr-1) and canopy architectures, capturing between 65-95% of incident radiation. Such values resulted in an average light use efficiency of 1.8 g MJ-1, ranging from 0.16 to 3.14 g MJ-1. Although different levels, light use efficiency values for the clones fluctuated similarly. Incident radiation was the main variable affecting the efficiency of dry matter conversion, and ε values were positively related variables expressing periods of greater water availability and negatively related to periods of lower availability. Larger effective leaf area index (Le) values resulted in higher light interception, but the different canopy architectures revealed different light capture strategies (0.3 < κ < 0.6). Despite a higher interception, there was no significant correlation with productivity; however there was a strong correlation between light use efficiency and wood growth, as a result of increased allocation to the stem. While evidencing the relationship between allocation and efficiency, there are other mechanisms associated with changes in ε observed that only one full characterization of the carbon fluxes can elucidate.

As relações hídricas, o crescimento e a biomassa da parte aérea e radicular foram determinadas em plantas jovens de Quercus suber L., regadas e em stresse hídrico que cresceram em mini-rizotrões, com e sem poliacrilato de sódio reticulado, e em vasos, em estufa, e transplantadas para uma parcela onde se aplicou poliacrilato de sódio reticulado e não reticulado, localizada na Herdade do Monte Fava, na região Sudoeste (SW) de Portugal Continental, a cerca de 154 km a Sul de Lisboa. A translocação e repartição do carbono recém-fotoassimilado no final da Primavera foi determinada em plantas jovens de Q. suber L., regadas que cresceram em contentores ao ar livre na Tapada Nacional das Necessidades, em Lisboa. Mais de 40% do 14C total recuperado nas plantas permaneceu nas folhas marcadas. Porém, as folhas marcadas do topo retiveram mais 14C(65% do total) do que as folhas marcadas inferiores (49%) e médias (44%). As folhas não marcadas e os ramos correspondentes apresentaram a menor força sink, tendo acumulado 0 a 3% do 14C total recuperado nas plantas, independentemente da posição das folhas marcadas. As porções dos ramos respeitantes às folhas marcadas acumularam de 11 a 20% do 14Ctotal recuperado nas plantas, constituindo sinks apreciáveis. As raízes; exibiram a maior força sink para o 14Ctotal recuperado nas plantas. Porém, a posição das folhas marcadas afectou a repartição do carbono recém-assimilado para as raízes. As raízes de sobreiros com as folhas inferiores marcadas acumularam 36% dos quais 21% foram repartidos para as raízes mais profundas. As raízes das plantas com as folhas médias marcadas acumularam 27%, dos quais 12% se concentraram na parte superior do sistema radicular. Nas plantas em que as folhas marcadas foram as do topo, as raízes acumularam apenas 16%. Os resultados demonstram que no final da Primavera, quando o surto anual de expansão foliar está no seu final, a maior sink para o carbono recém-assímilado são as raízes e as folhas basais são as principais exportadoras de carbono assimilado. ### Abstract - Water relations, growth and biomass were determined in young Quercus suber L. seedlings. These plants were grown in a greenhouse under well-watered and moderate and severe water deficit conditions. The seedlings were also grown with cross linked sodium polyacrylate in minirhizotrons. In the field, the seedlings were grown with sodium polyacrylates (cross linked and not cross linked). Allocation patterns, of recently assimilated carbon by Quercus suber L. seedlings were evaluated in late spring. 14CO2 was separately assimilated by lower, middle and top leaves. More than 40% of the 14Crecovered by the plants remained in the labeled leaves. However, top labeled leaves retained more 14C(65% of the total) than lower (49%) or middle (44%) ones. Both unlabeled leaves and their branches presented the least sink strength and accumulated from 0 to 3% of the total 14C recovered by the plants, regardless of the labeled leaves position. Branches of the labeled leaves accumulated 11 to 20 % of the total 14C recovered by the plants. These branches were appreciable sinks. Roots displayed the greatest sink strength for the total 14Crecovered by the plants. However, labeled leaves position affected the amount of 14Callocated to the root system. Roots of cork oak plants with lower labeled leaves accumulated 36 % being 21 % allocated to the deeper roots. In plants with middle labeled leaves, roots accumulated 27 %, being 12 % were at the superior zone of the root system. Roots only accumulated 16 % in plants with top, labeled leaves. Our results showed that root system was the major sink for recently assimilated carbon in late spring, when the growth flash of new shoots was over. Basal leaves were the main exporters of assimilated carbon.

Abstract Mycorrhizal fungi are important contributors to the functioning of boreal forests, since they act in the bilateral carbon and nutrient transport between above- and belowground parts of the ecosystem. In ectomycorrhizal (ECM) symbiosis of woody host plants, both fungal and plant partners depend on resources provided by the other. A single tree may simultaneously host several ECM fungal partners, which greatly enhance the host's nutrient uptake. At the same time nearly 20% of host primary production is allocated to mycorrhizal fungi. Although fungi depend on host-derived carbon, it is poorly understood how reduced carbon availability, e.g., due to herbivory, affects the ECM fungal symbionts. In this thesis I studied the impact of simulated insect defoliation or mammal browsing on mycorrhizal fungi of boreal woody hosts. Quantitative and qualitative changes in biomass partitioning in different fungal compartments were detected. None of the experiments showed that defoliation or shoot clipping treatments reduced the intensity of ECM colonisation, while treatments often shifted fungal composition towards less biomass producing ECM morphotypes. Above- and belowground diversity in ECM symbionts tended to decrease due to shoot or foliar damage. In addition, in some cases defoliation also reduced fungal biomass in fine roots and decreased ECM sexual reproduction by reducing the number of sporocarps produced. Defoliation induced a similar response pattern in the host and in ECM fungi with a stronger response to increasing severity of treatment (e.g. degree of removed foliage or repeated years of defoliation). This was also confirmed when relating the effects of host and ECM fungal symbionts to defoliation using present and previously published data. The present results suggest that belowground adaptation of boreal trees to the changing environment is mediated by changes in fungal community or biomass partitioning. The lack of response in the intensity of ECM colonisation further emphasises the importance of the symbiosis to boreal trees.