Articles de revues : « Drought hypothesis »

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Vargas, Jesús, et Pilar Paneque. « Challenges for the Integration of Water Resource and Drought-Risk Management in Spain ». Sustainability 11, n^o 2 (9 janvier 2019) : 308. http://dx.doi.org/10.3390/su11020308.

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Droughts are risks characterized by their complexity, uncertainty, and a series of other features, which differentiate them from other natural disasters and affect the strategies designed to manage them. These characteristics highlight the close relationship between drought management and water resources management. The following hypothesis is raised in this study—unsatisfactory integration of a drought-risk and water resources management strategies, increases the vulnerability to drought. To corroborate this hypothesis, the Spanish case was analyzed, where droughts are a recurrent phenomenon, due to the Mediterranean climate. Starting from the Intergovernmental Panel on Climate Change (IPCC) framework, which has been proposed to characterize vulnerability as a function of exposure, sensitivity, and adaptive capacity, this study analyzed the vulnerability in the Spanish River Basin Districts, through—(i) the integration of the predictable effects of climate change and the increased risk of exposure in hydrologic planning; (ii) the pressure on water resources that determines the sensitivity of the systems; and (iii) the development and implementation of drought management plans as a fundamental tool, in order to adapt before these events occur. The results showed that despite important advances in the process of conceiving and managing droughts, in Spain, there are still important gaps for an adequate integration of droughts risk into the water resource strategies. Therefore, despite the improvements, drought-risk vulnerability of the systems remained high.

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Leonard, Jenny, Adam G. West, Justin J. van Blerk et Fernando Ojeda. « Does drought limit resprouter recruitment in Erica ? A test using seeder and resprouter seedlings of Erica coccinea ». Australian Journal of Botany 69, n^o 8 (2021) : 554. http://dx.doi.org/10.1071/bt21015.

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Context It has been proposed that the distribution of resprouter and seeder Erica in the Cape Floristic Region (CFR) of South Africa is determined by drought rather than by fire frequency. Seedlings of Erica seeders are predicted to withstand the mild droughts of the southwest CFR better than those of Erica resprouters, which would account for the abundance of seeders in this region. Aims This study aimed to test this hypothesis using Erica coccinea (L.), which contains both a resprouter and a seeder form. Methods One-year-old seedlings of both forms were subjected to a progressively severe 50-day drought in the greenhouse. Key results Contrary to expectations, seeder seedlings had 67% higher mortality than resprouters during the initial phase of drought (30% vs 18% after 32days). However, both forms were unable to survive as the drought progressed, resulting in 95% mortality by Day50. There were limited differences between the forms in gas exchange and water potential, and no difference in root:shoot ratios. However, resprouters had significantly higher soluble carbohydrates than did seeders, which may have aided in delaying mortality. Conclusions Our results showed no evidence of resprouter seedlings being more vulnerable to mild drought than seeders in E. coccinea. Implications Our findings challenge the hypothesis that the distribution of this species can be explained by the vulnerability of resprouter seedlings to mild drought.

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Evans, Bethany A., et Victoria A. Borowicz. « The plant vigor hypothesis applies to a holoparasitic plant on a drought-stressed host ». Botany 93, n^o 10 (octobre 2015) : 685–89. http://dx.doi.org/10.1139/cjb-2015-0099.

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Parasitic plants extract resources from host vascular tissues but their responses to environmental fluctuation experienced by the host are poorly studied. Three frequently-cited hypotheses for effects of environmental stress on plant resistance to herbivores predict decreased, increased, or fluctuation in herbivore performance in response to drought stress. We tested which hypothesis best accounts for how drought stress applied to a perennial herb affects growth of the holoparasite, Cuscuta gronovii Willd. ex Roem. & Schult. (common dodder), an obligate shoot parasite. Verbesina alternifolia (L.) Britton ex Kearney (wingstem) supporting single, young C. gronovii were exposed to continuous, pulsed, or no water stress for 32 days and then dry mass of each parasite was determined. Consistent with the plant vigor hypothesis, C. gronovii grew significantly better on well-watered hosts. Continuous and pulsed drought stress of the host resulted in similar growth reduction relative to no drought stress. In addition to reducing absolute growth of the holoparasite, continuous and pulsed drought stress reduced the growth of the holoparasite relative to host growth. Although functionally similar to insect phloem feeders, growth of holoparasites such as C. gronovii is constrained by source–sink relations. Our results suggest drought stress experienced by a host weakens source strength and reduces uptake by the holoparasite acting as a sink.

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Stevenson, Samantha, Axel Timmermann, Yoshimitsu Chikamoto, Sally Langford et Pedro DiNezio. « Stochastically Generated North American Megadroughts ». Journal of Climate 28, n^o 5 (26 février 2015) : 1865–80. http://dx.doi.org/10.1175/jcli-d-13-00689.1.

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Abstract The importance of interannual-to-decadal sea surface temperature (SST) influences on drought in the United States is examined using a suite of simulations conducted with the T31×3 resolution version of the NCAR Community Earth System Model (CESM1.0.3). The model captures tropical Pacific teleconnections to North American precipitation reasonably well, although orographic features are somewhat enhanced at higher resolution. The contribution of SST anomalies is isolated by comparing two idealized, 1000-yr CESM1.0.3 experiments: a fully coupled control and an atmosphere-only (CAM4) run forced with the SST climatology from the control. Droughts are identified using the Palmer Drought Severity Index (PDSI), which is computed over four U.S. regions from the CESM1.0.3 experiments and compared with the North American Drought Atlas (NADA). The CESM1.0.3 reproduces the persistence of NADA droughts quite well, although the model underestimates drought severity. Within the CESM1.0.3 framework, SST forcing does not significantly affect drought intensity or frequency of occurrence, even for very persistent “megadroughts” of 15 yr or more in length. In both the CESM1.0.3 and NADA, with the exception of the Southeast United States, droughts in all regions have intensities, persistence lengths, and occurrence frequencies statistically consistent with a red noise null hypothesis. This implies that SST forcing is not the dominant factor in generating drought and therefore that many decadal megadroughts are caused by a combination of internal atmospheric variability and coupling with the land surface, with SST anomalies playing only a secondary role.

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Kriger, Kerry M. « Lack of Evidence for the Drought-linked Chytridiomycosis Hypothesis ». Journal of Wildlife Diseases 45, n^o 2 (avril 2009) : 537–41. http://dx.doi.org/10.7589/0090-3558-45.2.537.

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Kuśmierek-Tomaszewska, Renata, et Jacek Żarski. « Assessment of Meteorological and Agricultural Drought Occurrence in Central Poland in 1961–2020 as an Element of the Climatic Risk to Crop Production ». Agriculture 11, n^o 9 (7 septembre 2021) : 855. http://dx.doi.org/10.3390/agriculture11090855.

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The results of numerous studies concerning meteorological drought show that there is a considerable impact of this phenomenon on several regions in Europe. On the other hand, statistical trends of dry spell occurrences in some areas of the continent are unclear or even negative. Therefore, further research should be directed towards a better understanding of this hazard, particularly the seasonal changes, in order to elaborate adequate strategies to prevent and mitigate its undesirable effects. The main goal of the work, conducted as part of the research strategy on contemporary climate change, was to confirm the hypothesis of increasing frequency and intensity of droughts during the period of active plant growth and development (May–August) in central Poland in 1961–2020. The prevailing rainfall conditions in this period determine the production and economic effects of agricultural output. The analysis covered a multiannual period, including two separate climate normals: 1961–1990 and 1991–2020. The work is also aimed at detecting relationships between indicators characterizing meteorological drought (the Standardized Precipitation Index—SPI) and agricultural drought (the actual precipitation deficiency—PAdef). It was found that the frequency of meteorological droughts in the studied period amounts to 30.0% (severe and extreme constitute 6.7%). No significant increase in the frequency and intensity of meteorological droughts over time was observed. Relationships between meteorological and agricultural drought indicators were significant, so the SPI can be considered an indicator of plant irrigation needs in the studied area.

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Chammakhi, Chaima, Alexandre Boscari, Marie Pacoud, Grégoire Aubert, Haythem Mhadhbi et Renaud Brouquisse. « Nitric Oxide Metabolic Pathway in Drought-Stressed Nodules of Faba Bean (Vicia faba L.) ». International Journal of Molecular Sciences 23, n^o 21 (27 octobre 2022) : 13057. http://dx.doi.org/10.3390/ijms232113057.

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Drought is an environmental stress that strongly impacts plants. It affects all stages of growth and induces profound disturbances that influence all cellular functions. Legumes can establish a symbiosis with Rhizobium-type bacteria, whose function is to fix atmospheric nitrogen in organs called nodules and to meet plant nitrogen needs. Symbiotic nitrogen fixation (SNF) is particularly sensitive to drought. We raised the hypothesis that, in drought-stressed nodules, SNF inhibition is partly correlated to hypoxia resulting from nodule structure compaction and an increased O2 diffusion barrier, and that the nodule energy regeneration involves phytoglobin–nitric oxide (Pgb–NO) respiration. To test this hypothesis, we subjected faba bean (Vicia faba L.) plants nodulated with a Rhizobium laguerreae strain to either drought or osmotic stress. We monitored the N2-fixation activity, the energy state (ATP/ADP ratio), the expression of hypoxia marker genes (alcohol dehydrogenase and alanine aminotransferase), and the functioning of the Pgb–NO respiration in the nodules. The collected data confirmed our hypothesis and showed that (1) drought-stressed nodules were subject to more intense hypoxia than control nodules and (2) NO production increased and contributed via Pgb–NO respiration to the maintenance of the energy state of drought-stressed nodules.

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Wilschut, Rutger A., et Mark van Kleunen. « Drought alters plant‐soil feedback effects on biomass allocation but not on plant performance ». Plant and Soil 462, n^o 1-2 (10 février 2021) : 285–96. http://dx.doi.org/10.1007/s11104-021-04861-9.

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Abstract Aims Drought events can alter the composition of plant and soil communities, and are becoming increasingly common and severe due to climate change. However, how droughts affect plant-soil feedbacks is still poorly understood. Plants accumulate species-specific rhizosphere communities, and droughts may have varying impacts across plant species and soil biota. We therefore tested the hypothesis that drought alters plant-soil feedbacks differently among closely related plant species that differ in their preferences for soil moisture. Methods In a two-phase greenhouse experiment, we first conditioned grassland soil with seven Geranium species and, as controls, we conditioned soil with a grass species or left soil unplanted. In the second phase, we grew the Geranium species in conspecific, grass-conditioned and unplanted soil, maintained soil moisture at 5 %, 10 % or 20 % (w/w), and determined biomass responses after 35 days. Results Independent of conditioning, plants showed a weaker performance with decreasing soil moisture. Under the driest conditions, soil conditioning by conspecifics most negatively affected relative root weight in comparison to plants growing in unplanted control soil, while the effects of conspecific conditioning on relative root weights were species-specific when compared to plants grown in grass-conditioned control soil. Conclusions We conclude that decreased soil moisture modified plant-soil feedback effects on biomass allocation, and that these modifications acted in species-specific ways. However, drought effects on plant-soil feedbacks were subtle, and did not affect overall plant performance. Therefore, plant-soil feedback effects on plant performance during a drought event may be limited in comparison with the direct effects of drought.

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Hamzelou, Sara, Karthik Shantharam Kamath, Farhad Masoomi-Aladizgeh, Matthew M. Johnsen, Brian J. Atwell et Paul A. Haynes. « Wild and Cultivated Species of Rice Have Distinctive Proteomic Responses to Drought ». International Journal of Molecular Sciences 21, n^o 17 (19 août 2020) : 5980. http://dx.doi.org/10.3390/ijms21175980.

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Drought often compromises yield in non-irrigated crops such as rainfed rice, imperiling the communities that depend upon it as a primary food source. In this study, two cultivated species (Oryza sativa cv. Nipponbare and Oryza glaberrima cv. CG14) and an endemic, perennial Australian wild species (Oryza australiensis) were grown in soil at 40% field capacity for 7 d (drought). The hypothesis was that the natural tolerance of O. australiensis to erratic water supply would be reflected in a unique proteomic profile. Leaves from droughted plants and well-watered controls were harvested for label-free quantitative shotgun proteomics. Physiological and gene ontology analysis confirmed that O. australiensis responded uniquely to drought, with superior leaf water status and enhanced levels of photosynthetic proteins. Distinctive patterns of protein accumulation in drought were observed across the O. australiensis proteome. Photosynthetic and stress-response proteins were more abundant in drought-affected O. glaberrima than O. sativa, and were further enriched in O. australiensis. In contrast, the level of accumulation of photosynthetic proteins decreased when O. sativa underwent drought, while a narrower range of stress-responsive proteins showed increased levels of accumulation. Distinctive proteomic profiles and the accumulated levels of individual proteins with specific functions in response to drought in O. australiensis indicate the importance of this species as a source of stress tolerance genes.

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Kuśmierek-Tomaszewska, Renata, Jacek Żarski et Stanisław Dudek. « Assessment of Irrigation Needs in Sugar Beet (Beta vulgaris L.) in Temperate Climate of Kujawsko-Pomorskie Region (Poland) ». Agronomy 9, n^o 12 (28 novembre 2019) : 814. http://dx.doi.org/10.3390/agronomy9120814.

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The primary purpose of this work was to assess the need for irrigation in sugar beet cultivated in the temperate climate of the Kujawsko-Pomorskie region of Poland based on meteorological data from the period 1981–2010. The work was also aimed at determining the tendency of changes in the frequency and intensity of droughts during the period of high water needs for sugar beets (spanning July–August) and confirming the hypothesis that agricultural drought may be identified based on the indicator of meteorological drought—Standardized Precipitation Index (SPI). The occurrence of meteorological droughts amounted to 26.7–40.0%, depending on location. No significant trend of increasing dryness was found; however, quite the opposite, an upward tendency was identified, which indicates an improvement of precipitation conditions over time. It was found that sugar beet production in a temperate climate is carried out in the conditions of precipitation deficits, which amount to an average of 32–49 mm and a maximum of 112–173 mm in July–August, but the deficits showed neither significant nor targeted changes with time. A strong, significant relationship between meteorological (SPI) and agricultural (Pdef) drought indicators allows for a determination of sugar beet irrigation needs solely based on information on normalized precipitation values (SPI).

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Nardini, Andrea, Eele Õunapuu-Pikas et Tadeja Savi. « When smaller is better : leaf hydraulic conductance and drought vulnerability correlate to leaf size and venation density across four Coffea arabica genotypes ». Functional Plant Biology 41, n^o 9 (2014) : 972. http://dx.doi.org/10.1071/fp13302.

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Leaf hydraulic conductance (Kleaf) and drought vulnerability in terms of leaf water potential inducing 50% loss of Kleaf (P50), were assessed in four genotypes of Coffea arabica L. We tested three hypotheses: (1) leaf P50 is lower in small leaves with higher vein densities; (2) lower P50 translates into lower Kleaf, limiting gas exchange rates and higher leaf mass per unit area (LMA); (3) P50 values are coordinated with symplastic drought tolerance. We found partial support for Hypotheses 1 and 3, but not for Hypothesis 2. Significant correlations existed among leaf size, vein network and drought resistance. Smaller leaves displayed higher major vein density, higher Kleaf and more negative P50. Kleaf was correlated with leaf gas exchange rates. A negative relationship was observed between Kleaf and LMA, whereas P50 was found to be positively correlated with LMA. Across coffee genotypes, reduced leaf surface area and increased vein density shifts P50 towards more negative values while not translating into higher LMA or lower Kleaf. Breeding crop varieties for both increased safety of the leaf hydraulic system towards drought-induced dysfunction and high gas exchange rates per unit of leaf area is probably a feasible target for future adaptation of crops to climate change scenarios.

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Kilpeläinen, Jouni, Pedro J. Aphalo, Aitor Barbero-López, Bartosz Adamczyk, Sammi Alam Nipu et Tarja Lehto. « Are arbuscular-mycorrhizal Alnus incana seedlings more resistant to drought than ectomycorrhizal and nonmycorrhizal ones ? » Tree Physiology 40, n^o 6 (18 mars 2020) : 782–95. http://dx.doi.org/10.1093/treephys/tpaa035.

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Abstract Arbuscular mycorrhizas (AMs) prevail in warm and dry climates and ectomycorrhizas (EMs) in cold and humid climates. We suggest that the fungal symbionts benefit their host plants especially in the corresponding conditions. The hypothesis tested was that AM plants are more drought-resistant than EM or nonmycorrhizal (NM) plants. Grey alder (Alnus incana (L.) Moench) seedlings were inoculated with two species of either AM or EM fungi or none. In one controlled-environment experiment, there was a watering and a drought treatment. Another set of seedlings were not watered until permanent wilting. The AM plants were somewhat smaller than EM and NM, and at the early stage of the drought treatment, the soil-moisture content was slightly higher in the AM pots. Shoot water potential was highest in the AM treatment during severe drought, while stomatal conductance and photosynthesis did not show a mycorrhizal effect. In the lethal-drought set, the AM plants maintained their leaves longer than EM and NM plants, and the AM seedlings survived longer than NM seedlings. Foliar phosphorus and sulfur concentrations remained higher in AM plants than EM or NM, but potassium, copper and iron increased in EM during drought. The root tannin concentration was lower in AM than EM and drought doubled it. Although the difference in drought resistance was not large, the hypothesis was supported by the better performance of AM plants during a severe short-term drought. Sustained phosphorus nutrition during drought in AM plants was a possible reason for this. Moreover, the higher foliar sulfur and lower metal-nutrient concentrations in AM may reflect differences in nutrient uptake or (re)translocation during drought, which merit further research. The much larger tannin concentrations in EM root systems than AM did not appear to protect the EM plants from drought. The differential tannin accumulation in AM and EM plants needs further attention.

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Kim, Daeha, et Jinyoung Rhee. « A drought index based on actual evapotranspiration from the Bouchet hypothesis ». Geophysical Research Letters 43, n^o 19 (11 octobre 2016) : 10,277–10,285. http://dx.doi.org/10.1002/2016gl070302.

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Maréchaux, Isabelle, Megan K. Bartlett, Amaia Iribar, Lawren Sack et Jérôme Chave. « Stronger seasonal adjustment in leaf turgor loss point in lianas than trees in an Amazonian forest ». Biology Letters 13, n^o 1 (janvier 2017) : 20160819. http://dx.doi.org/10.1098/rsbl.2016.0819.

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Pan-tropically, liana density increases with decreasing rainfall and increasing seasonality. This pattern has led to the hypothesis that lianas display a growth advantage over trees under dry conditions. However, the physiological mechanisms underpinning this hypothesis remain elusive. A key trait influencing leaf and plant drought tolerance is the leaf water potential at turgor loss point ( π tlp ). π tlp adjusts under drier conditions and this contributes to improved leaf drought tolerance. For co-occurring Amazonian tree ( n = 247) and liana ( n = 57) individuals measured during the dry and the wet seasons, lianas showed a stronger osmotic adjustment than trees. Liana leaves were less drought-tolerant than trees in the wet season, but reached similar drought tolerances during the dry season. Stronger osmotic adjustment in lianas would contribute to turgor maintenance, a critical prerequisite for carbon uptake and growth, and to the success of lianas relative to trees in growth under drier conditions.

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Ash, Konstantin, et Nick Obradovich. « Climatic Stress, Internal Migration, and Syrian Civil War Onset ». Journal of Conflict Resolution 64, n^o 1 (25 juillet 2019) : 3–31. http://dx.doi.org/10.1177/0022002719864140.

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Syria recently suffered a once in 500-year meteorological drought followed by one of the worst conflicts of the twenty-first century. We exploit subnational variation in drought impact to examine associations between climatic stress and Syria’s political unrest. Climatic stress may produce instability through both immediate hardship and, indirectly, internal migration. Consistent with the internal migration hypothesis, we find less severely drought-stricken Syrian regions more likely to experience protest. We employ nighttime lights as a proxy for population density to examine the association between climatic stress and internal displacement. We find climatic stress decreased nighttime light intensity during the drought period. Increases in nighttime lights from 2005 to 2010 are associated with added risk of protest in Sunni Arab areas, suggesting an influx of migrants bolstered local grievances. Our findings support the internal migration hypothesis and suggest extreme climate events may impact civil unrest via geographically and temporally indirect paths.

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Curran, Timothy J., Peter J. Clarke et Nigel W. M. Warwick. « Water relations of woody plants on contrasting soils during drought : does edaphic compensation account for dry rainforest distribution ? » Australian Journal of Botany 57, n^o 8 (2009) : 629. http://dx.doi.org/10.1071/bt09128.

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The occurrence of dry rainforest in climates considered drier than the recognised limit for rainforest has been explained by the edaphic compensation hypothesis, which proposed that finer-textured soils facilitate the occurrence of rainforest at climatic extremes. We tested this by examining the effect of soil type on the water relations and plant traits of four dry rainforest species, during a severe drought and subsequent non-drought periods. We predicted plants growing in sandy soils would exhibit higher levels of water stress (lower predawn water potential and stomatal conductance) and possess morphological and physiological traits that more typically reflect drought resistance (late leaf fall in deciduous species, low specific leaf area, vertical leaf angles and stomata that close at low water potential) than those growing in loam soils. During drought, levels of water stress were similar across soil types, while post-drought plants on sandy soils were less stressed. Soil type did not cause shifts in drought tolerance traits, suggesting there has been no ecotypic differentiation of dry rainforest species across soil types for these traits. Hence, we found no support for the edaphic compensation hypothesis in adult plants; future studies should consider other life-cycle stages, such as seedlings.

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Rull, Valentí. « Drought, freshwater availability and cultural resilience on Easter Island (SE Pacific) during the Little Ice Age ». Holocene 30, n^o 5 (5 janvier 2020) : 774–80. http://dx.doi.org/10.1177/0959683619895587.

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After decades of human-deterministic explanations for the collapse of the ancient Rapanui culture that inhabited Easter Island (Rapa Nui) before European contact (1722 CE), paleoecological studies developed over the last decade have provided sound evidence of climate changes and their potential socioecological impacts. Especially significant is the occurrence of a century-scale drought (1570–1720 CE) during the Little Ice Age (LIA). Freshwater is a critical resource on Easter Island that heavily depends on rain, which maintains the only three permanent surficial freshwater sources on the island: two lakes (Rano Kao and Rano Raraku) and a marsh (Rano Aroi). Under these conditions, the LIA drought could have significantly affected human life; however, the Rapanui society remained healthy, showing remarkable resilience. There are two main hypotheses on how the ancient Rapanui could have obtained freshwater to guarantee their continuity. One of these hypotheses proposes that Lake Kao was a permanent source of freshwater, even during the LIA drought, which led to some intraisland cultural and population reorganizations. The coastal groundwater hypothesis dismisses the use of lakes and other surficial freshwater sources to maintain the water-stressed Rapanui population and contends that the only routine freshwater sources during the LIA drought were the abundant and widespread coastal seeps fed by fresh/brackish groundwater. The pros and cons of these two hypotheses are discussed on the basis of the available archeological and paleoecological evidence, and it is concluded that given the present state of knowledge, neither can be rejected. Therefore, these two proposals could be complementary rather than mutually exclusive.

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BLAIN, GABRIEL CONSTANTINO, et ANA CAROLINA FREITAS XAVIER. « TRANSFORMING THE PALMER DROUGHT SEVERITY INDEX INTO A STANDARDIZED MULTI-SCALAR INDEX : ASSESSING THE NORMALITY ASSUMPTION UNDER SOUTH AMERICA TROPICAL-SUBTROPICAL CONDITIONS ». Experimental Agriculture 55, n^o 5 (17 août 2018) : 752–64. http://dx.doi.org/10.1017/s0014479718000340.

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SUMMARYTwo of the most common criticisms over the widely used Palmer Drought Severity Index (PDSI) is that it cannot be calculated at different time scales and it is not as spatially comparable as other Standardized Drought Indices (SDI), such as the Standardized Precipitation Index (SPI). Therefore, the hypothesis that the PDSI may be transformed into a multi-scalar index sharing the same normalized nature of others SDI has been proposed in the scientific literature. This hypothesis was extensively evaluated in this study by statistical methods largely used to assess and improve the performance of others standardized drought indices (e.g. SPI). In general terms, these methods evaluated the ability of the transformed/probability-based Palmer's Index to approach the standard normal distribution. The strategy of basing the selection of a distribution for calculating such an index on its performance within the range of typical drought and flood events was adopted. The testing region was the State of São Paulo, a tropical-subtropical region of Brazil. Time scales ranging from 1- to 12-month and Available Water Capacity equal to 50, 100 and 150 mm were also considered. A computational algorithm for calculating the new version of the Palmer's index is also provided. The Generalized Logistic distribution with parameters estimated by the maximum likelihood method is recommended to calculate the new index. The results of the normality tests are consistent with the above-mentioned strategy. From a scientific standpoint, the results support the hypothesis of this study. Therefore, we conclude that the new Standardized Palmer Drought Index (SPDI) is capable of meeting the normally assumption under tropical-subtropical climatic conditions of Brazil. In other words, the new SPDI has shown to be capable of representing floods and drought events in a similar probabilistic/normalized way. This conclusion holds true for time scales ranging from 1- to 12-month and Available Water Capacity equal to 50, 100 and 150 mm.

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Kemp, W. P., et M. M. Cigliano. « DROUGHT AND RANGELAND GRASSHOPPER SPECIES DIVERSITY ». Canadian Entomologist 126, n^o 4 (août 1994) : 1075–92. http://dx.doi.org/10.4039/ent1261075-4.

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AbstractRangeland grasshopper species richness was monitored at 10 sites in Montana, U.S.A., during 1986 through 1992, which included an extreme drought year (1988). We observed significant post-1988 drought reductions in rangeland grasshopper species richness in the eastern and south-central region of Montana where drought intensity has been increasing during the past 20 years. In the north-central region, which also experienced the 1988 drought but showed no long-term drought trend, we did not observe a post-drought reduction in overall rangeland grasshopper species richness. Thus, in terms of rangeland grasshopper species richness, the potential impact of a severe drought in a given year may depend on the timing of such an event within longer-term climatic cycles. Our findings suggest that as regional drought intensity increases temporally, there may be an increased likelihood that a single extreme drought year will not only have a profound impact on abundance but may also result in significant long-term reduction of grasshopper species richness. Our results support the hypothesis that resource limitation is a very important factor in structuring rangeland grasshopper communities in space and time.

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Hong, Xingjun, Shenglian Guo, Guiya Chen, Na Guo et Cong Jiang. « A Modified Two-Parameter Monthly Water Balance Model for Runoff Simulation to Assess Hydrological Drought ». Water 14, n^o 22 (16 novembre 2022) : 3715. http://dx.doi.org/10.3390/w14223715.

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Quantitative assessment of the frequency and magnitude of drought events plays an important role in preventing drought disasters and ensuring water security in river basins. In this paper, we modified a parsimonious two-parameter monthly water balance (TPMWB) model by incorporating the generalized proportionality hypothesis with precipitation and potential evapotranspiration as input variables. The modified TPMWB was then used to simulate the monthly hydrological processes of 30 sub-basins in the Han River basin. It is shown that the water balance model can satisfactorily simulate the hydrological regimes in the selected sub-basins. We derived the probability distribution functions of monthly runoff using the principle of maximum entropy to calculate the Standardized Runoff Index (SRI), and assessed the historical hydrological drought conditions. By investigating the correlation between four major drought characteristics (i.e., drought duration, drought severity, drought intensity, and drought inter-arrival time) and four dimensionless parameters representing the climatic and underlying properties of the basin, a conclusion can be drawn that the formation and development of hydrological drought in the Han River basin is mainly controlled by watershed storage factors, and the influence of climatic factors is also significant. The proposed approach provides a potential alternative for regional drought early warning and under changing environmental conditions.

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Zhang, Ya-Li, Yuan-Yuan Hu, Hong-Hai Luo, Wah Soon Chow et Wang-Feng Zhang. « Two distinct strategies of cotton and soybean differing in leaf movement to perform photosynthesis under drought in the field ». Functional Plant Biology 38, n^o 7 (2011) : 567. http://dx.doi.org/10.1071/fp11065.

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This paper reports an experimental test of the hypothesis that cotton and soybean differing in leaf movement have distinct strategies to perform photosynthesis under drought. Cotton and soybean were exposed to two water regimes: drought stressed and well watered. Drought-stressed cotton and soybean had lower maximum CO2 assimilation rates than well-watered (control) plants. Drought reduced the light saturation point and photorespiration of both species – especially in soybean. Area-based leaf nitrogen decreased in drought-stressed soybean but increased in drought-stressed cotton. Drought decreased PSII quantum yield (ΦPSII) in soybean leaves, but increased ΦPSII in cotton leaves. Drought induced an increase in light absorbed by the PSII antennae that is dissipated thermally via ΔpH- and xanthophylls-regulated processes in soybean leaves, but a decrease in cotton leaves. Soybean leaves appeared to have greater cyclic electron flow (CEF) around PSI than cotton leaves and drought further increased CEF in soybean leaves. In contrast, CEF slightly decreased in cotton under drought. These results suggest that the difference in leaf movement between cotton and soybean leaves gives rise to different strategies to perform photosynthesis and to contrasting photoprotective mechanisms for utilisation or dissipation of excess light energy. We suggest that soybean preferentially uses light-regulated non-photochemical energy dissipation, which may have been enhanced by the higher CEF in drought-stressed leaves. In contrast, cotton appears to rely on enhanced electron transport flux for light energy utilisation under drought, for example, in enhanced nitrogen assimilation.

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Muths, E., R. D. Scherer, S. M. Amburgey, T. Matthews, A. W. Spencer et P. S. Corn. « First estimates of the probability of survival in a small-bodied, high-elevation frog (Boreal Chorus Frog, Pseudacris maculata), or how historical data can be useful ». Canadian Journal of Zoology 94, n^o 9 (septembre 2016) : 599–606. http://dx.doi.org/10.1139/cjz-2016-0024.

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In an era of shrinking budgets yet increasing demands for conservation, the value of existing (i.e., historical) data are elevated. Lengthy time series on common, or previously common, species are particularly valuable and may be available only through the use of historical information. We provide first estimates of the probability of survival and longevity (0.67–0.79 and 5–7 years, respectively) for a subalpine population of a small-bodied, ostensibly common amphibian, the Boreal Chorus Frog (Pseudacris maculata (Agassiz, 1850)), using historical data and contemporary, hypothesis-driven information–theoretic analyses. We also test a priori hypotheses about the effects of color morph (as suggested by early reports) and of drought (as suggested by recent climate predictions) on survival. Using robust mark–recapture models, we find some support for early hypotheses regarding the effect of color on survival, but we find no effect of drought. The congruence between early findings and our analyses highlights the usefulness of historical information in providing raw data for contemporary analyses and context for conservation and management decisions.

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Velikova, Violeta, Carmen Arena, Luigi Gennaro Izzo, Tsonko Tsonev, Dimitrina Koleva, Massimiliano Tattini, Olympia Roeva, Anna De Maio et Francesco Loreto. « Functional and Structural Leaf Plasticity Determine Photosynthetic Performances during Drought Stress and Recovery in Two Platanus orientalis Populations from Contrasting Habitats ». International Journal of Molecular Sciences 21, n^o 11 (30 mai 2020) : 3912. http://dx.doi.org/10.3390/ijms21113912.

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In the context of climatic change, more severe and long-lasting droughts will modify the fitness of plants, with potentially worse consequences on the relict trees. We have investigated the leaf phenotypic (anatomical, physiological and biochemical) plasticity in well-watered, drought-stressed and re-watered plants of two populations of Platanus orientalis, an endangered species in the west of the Mediterranean area. The two populations originated in contrasting climate (drier and warmer, Italy (IT) population; more humid and colder, Bulgaria (BG) population). The IT control plants had thicker leaves, enabling them to maintain higher leaf water content in the dry environment, and more spongy parenchyma, which could improve water conductivity of these plants and may result in easier CO2 diffusion than in BG plants. Control BG plants were also characterized by higher photorespiration and leaf antioxidants compared to IT plants. BG plants responded to drought with greater leaf thickness shrinkage. Drought also caused substantial reduction in photosynthetic parameters of both IT and BG plants. After re-watering, photosynthesis did not fully recover in either of the two populations. However, IT leaves became thicker, while photorespiration in BG plants further increased, perhaps indicating sustained activation of defensive mechanisms. Overall, our hypothesis, that plants with a fragmented habitat (i.e., the IT population) lose phenotypic plasticity but acquire traits allowing better resistance to the climate where they became adapted, remains confirmed.

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Statwick, Joseph M., Anna K. Williams et Anna A. Sher. « Lack of Evidence for the Drought Tolerance Hypothesis of Hyperaccumulation in Astragalus Species ». International Journal of Plant Sciences 178, n^o 6 (juillet 2017) : 478–84. http://dx.doi.org/10.1086/692087.

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Zhou, Shuang-Xi, Rob R. Walker et Everard Edwards. « Decoupled drought responses of fine-root versus leaf acquisitive traits among six Prunus hybrids ». Journal of Plant Ecology 13, n^o 3 (13 avril 2020) : 304–12. http://dx.doi.org/10.1093/jpe/rtaa015.

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Abstract Aims Predicting drought consequences on forests and fruit crop plantings requires improved understanding of drought responses of both leaf and fine-root resource acquisitive traits (specific leaf area—SLA, specific root surface area—SRA and specific root length—SRL). We hypothesize their responses are coordinated towards integrated plant resource conservation under severe drought. Methods We tested the hypothesis with a greenhouse-based drought experiment on saplings of six Prunus hybrids with a priori known contrasting drought sensitivity. Saplings were subjected to either control (100% field capacity) or severe drought stress treatment (33% evapotranspiration of hybrid-specific control plants). Sample collections were carried out at 30 and at 60 days after the start of treatments, for both control and stressed saplings. Important Findings No hybrid showed concurrent significant decrease of SLA and SRA (or SRL) under severe drought. The fine-root traits of the six hybrids showed two major drought-response scenarios, in particular: (i) increased root tissue density (RTD) and decreased average root diameter without significant change of SRL and (ii) increased RTD and decreased SRL without significant change of average root diameter. Drought responses of leaf gas exchange, SRA, SRL and RTD were closely correlated along a gradient towards resource conservation from control to drought-stressed plants in all hybrids, which was orthogonal to another gradient characterized by a hybrid-dependent decrease of SLA. These findings highlight (i) the multi-dimensionality of root-trait drought responses, (ii) the decoupling between leaf economics and leaf hydraulics and (iii) the covariation of leaf and root hydraulics in terms of trait drought responses. The study contributes to identifying the origin of the multi-dimensionality of root-trait drought response at intraspecific scale, and highlights differential drought–response combinations of leaf and fine-root traits among hybrids to survive under severe soil drought stress.

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Andrews, Anthony P. « The Fall of Chichen Itza : A Preliminary Hypothesis ». Latin American Antiquity 1, n^o 3 (septembre 1990) : 258–67. http://dx.doi.org/10.2307/972164.

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The fall of the Early Postclassic capital of Chichen Itza is generally described in native chronicles as the result of a widespread revolt of native Yucatec Maya against the Itzá rulers of northern Yucatan. This historic event was the outcome of complex social, economic, and ecological processes that ultimately led to the weakening and dissolution of the Itzá polity. The historic legends that trace the fall of the Itzá are a superficial manifestation of deeper problems, which likely included tense relations with subjugated peoples, excess economic and human tribute, overpopulation, scarcities of land and agricultural resources, and possible climatological changes resulting in drought. The Itzá economy was linked to all these processes, but as they primarily were focused on the exploitation of coastal resources and long-distance trade, they failed to establish a viable economic system in the interior. This failure, coupled with the overexploitation of a declining social and economic resource base, led to the Itzá collapse. This essay presents a preliminary discussion of these processes.

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Lee, Jin Wook, Kenneth W. Mudge et Joseph Lardner. « Effect of Drought Stress on Growth and Ginsenoside Content of American Ginseng ». HortScience 40, n^o 4 (juillet 2005) : 1116A—1116. http://dx.doi.org/10.21273/hortsci.40.4.1116a.

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American ginseng (Panax quinquefolium L.) contains pharmacologically active secondary compounds known as ginsenosides, which have been shown to be affected by both genetic and environmental factors. In this greenhouse experiment, we tested the hypothesis that ginsenosides would behave as “stress metabolites” and be associated with osmoregulation in response to drought stress. Two year-old seedlings, grown in 5-inch pots, were well watered for 40 days prior to the initiation of treatments. Plants in the drought stress treatment were watered every 20 days while the controls were watered every 10 days, and the experiment was terminated after 4 and 8 dry down cycles (80 days), respectively. Predawn leaf water potential and relative water content (RWC) of drought-stressed plants during a typical dry down cycle were lower than control plants. The diameter and weight of primary storage roots were decreased in the stressed treatment. The length of the main storage root and the longest secondary (fibrous) root were significantly increased by the drought stress treatment. Leaf chlorophyll content of drought-stressed plants was lower than controls. The osmotic potential of the drought-stressed ginseng was not lower than the control, indicating that ginsenoside is not involved in osmoregulation in response to drought stress. Furthermore, ginsenosides Rb1 and Rd, and total ginsenosides were significantly lower in primary roots of drought-stressed plants compared to control plants.

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Winkler, N., W. Weymann, H. Auge, S. Klotz, P. Finkenbein et H. Heilmeier. « Drought resistance of native pioneer species indicates potential suitability for restoration of post-mining areas ». Web Ecology 14, n^o 1 (9 janvier 2015) : 65–74. http://dx.doi.org/10.5194/we-14-65-2014.

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Abstract. In order to test whether invasive exotic species, predominantly used for restoring post-mining areas in north-eastern Vietnam, may be replaced by ecologically superior native pioneer species, we conducted a drought stress experiment in a greenhouse. We hypothesized that juvenile individuals of four native pioneer tree and two native pioneer grass species have a drought resistance comparable to two exotic reference species. Our results confirm this hypothesis: even under drought, native trees had a higher biomass and root : shoot ratio than exotic trees, although their maximum relative elongation rate and biomass were reduced more strongly than for exotic trees with respect to well-watered conditions. Native grasses had a higher root length density and a similar drought-induced reduction of stomatal conductance compared to exotic trees. In spite of a higher biomass reduction, native grasses produced more biomass under drought in absolute terms. Notwithstanding that further investigations of other adverse environmental factors need to be performed, our results indicate with respect to drought resistance that native pioneer species are a potential alternative to exotic species for the ecological restoration of subtropical post-mining areas, which may accelerate secondary succession.

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Hoekstra, N. J., J. A. Finn, D. Hofer et A. Lüscher. « The effect of drought and interspecific interactions on depth of water uptake in deep- and shallow-rooting grassland species as determined by δ18O natural abundance ». Biogeosciences 11, n^o 16 (25 août 2014) : 4493–506. http://dx.doi.org/10.5194/bg-11-4493-2014.

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Abstract. Increased incidence of drought, as predicted under climate change, has the potential to negatively affect grassland production. Compared to monocultures, vertical belowground niche complementarity between shallow- and deep-rooting species may be an important mechanism resulting in higher yields and higher resistance to drought in grassland mixtures. However, very little is known about the belowground responses in grassland systems and increased insight into these processes may yield important information both to predict the effect of future climate change and better design agricultural systems to cope with this. This study assessed the effect of a 9-week experimental summer drought on the depth of water uptake of two shallow-rooting species (Lolium perenne L. and Trifolium repens L.) and two deep-rooting species (Cichorium intybus L. and Trifolium pratense L.) in grassland monocultures and four-species mixtures by using the natural abundance δ18O isotope method. We tested the following three hypotheses: (1) drought results in a shift of water uptake to deeper soil layers, (2) deep-rooting species take up a higher proportion of water from deeper soil layers relative to shallow-rooting species, and (3) as a result of interspecific interactions in mixtures, the water uptake of shallow-rooting species becomes shallower when grown together with deep-rooting species and vice versa, resulting in reduced niche overlap. The natural abundance δ18O technique provided novel insights into the depth of water uptake of deep- and shallow- rooting grassland species and revealed large shifts in depth of water uptake in response to drought and interspecific interactions. Compared to control conditions, drought reduced the proportional water uptake from 0–10 cm soil depth (PCWU0–10) of L. perenne, T. repens and C. intybus in monocultures by on average 54%. In contrast, the PCWU0–10 of T. pratense in monoculture increased by 44%, and only when grown in mixture did the PCWU0–10 of T. pratense decrease under drought conditions. In line with hypothesis (2), in monoculture, the PCWU0–10 of shallow-rooting species L. perenne and T. repens was 0.53 averaged over the two drought treatments, compared to 0.16 for the deep-rooting C. intybus. Surprisingly, in monoculture, water uptake by T. pratense was shallower than for the shallow-rooting species (PCWU0–10 = 0.68). Interspecific interactions in mixtures resulted in a shift in the depth of water uptake by the different species. As hypothesised, the shallow-rooting species L. perenne and T. repens tended to become shallower, and the deep-rooting T. pratense made a dramatic shift to deeper soil layers (reduction in PCWU0–10 of 58% on average) in mixture compared to monoculture. However, these shifts did not result in a reduction in the proportional similarity of the proportional water uptake from different soil depth intervals (niche overlap) in mixtures compared to monocultures. There was no clear link between interspecific differences in depth of water uptake and the reduction of biomass production under drought compared to control conditions (drought resistance). Cichorium intybus, the species with water uptake from the deepest soil layers was one of the species most affected by drought. Interestingly, T. pratense, which was least affected by drought, also had the greatest plasticity in depth of water uptake. This suggests that there may be an indirect effect of rooting depth on drought resistance, as it determines the potential plasticity in the depth of water uptake.

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Silvério, Divino V., Robson Santana Oliveira, Bernardo Monteiro Flores, Paulo M. Brando, Hellen Kezia Almada, Marco Túlio Furtado, Fabio Garcia Moreira, Michael Heckenberger, Katia Yukari Ono et Marcia N. Macedo. « Intensification of fire regimes and forest loss in the Território Indígena do Xingu ». Environmental Research Letters 17, n^o 4 (21 mars 2022) : 045012. http://dx.doi.org/10.1088/1748-9326/ac5713.

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Abstract The contemporary fire regime of southern Amazonian forests has been dominated by interactions between droughts and sources of fire ignition associated with deforestation and slash-and-burn agriculture. Until recently, wildfires have been concentrated mostly on private properties, with protected areas functioning as large-scale firebreaks along the Amazon’s agricultural frontier. However, as the climate changes, protected forests have become increasingly flammable. Here, we have quantified forest degradation in the Território Indígena do Xingu (TIX), an iconic area of 2.8 million hectares where over 6000 people from 16 different ethnic Indigenous groups live across 100 villages. Our main hypothesis was that forest degradation, defined here as areas with lower canopy cover, inside the TIX is increasing due to pervasive sources of fire ignition, more frequent extreme drought events, and changing slash-and-burn agricultural practices. Between 2001 and 2020, nearly 189 000 hectares (∼7%) of the TIX became degraded by recurrent drought and fire events that were the main factors driving forest degradation, particularly in seasonally flooded forests. After three fire events, the probability of forest loss was higher in seasonally flooded areas (63%) compared to upland areas (41%). Given the same fire frequency, areas that have not suffered with extreme droughts showed a 24% lower probability of forest loss compared to areas that experienced three drought events. Distance from villages and human density also had a marked effect on forest cover loss, which was generally higher in areas close to the largest villages. In one of the most culturally diverse Indigenous lands of the Amazon, in a landscape highly threatened by deforestation, our findings demonstrate that climate change may have already exceeded the conditions to which the system has adapted.

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Augé, Robert, Keunho Cho, Jean Stutz et Heather Toler. « (319) Mycorrhizal Symbiosis and Response of Sorghum Plants to Combined Drought and Salt Stresses ». HortScience 40, n^o 4 (juillet 2005) : 1037C—1037. http://dx.doi.org/10.21273/hortsci.40.4.1037c.

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Colonization of roots by arbuscular mycorrhizal (AM) fungi can increase host resistance to drought stress, although the effect is unpredictable. Since AM symbiosis also frequently increases host resistance to salt stress, and since drought and salt stress are often linked in drying soils, we speculated that the AM influence on plant drought response may be linked to AM influence on salt stress. We tested the hypothesis that AM-induced effects on drought responses would be more pronounced when plants of comparable size are exposed to drought in salinized soils. In two greenhouse experiments, several water relations characteristics were measured in sorghum plants colonized by Glomus intraradices, Gigaspora margarita, or a mixture of AM species during a sustained drought following exposure to salt treatments (NaCl stress, osmotic stress, or soil leaching). The presence of excess salt in soils widened the difference in drought responses between AM and non-AM plants in just two instances: days needed for plants to reach stomatal closure, and promotion of stomatal conductance. In other instances, the addition of salt tended to nullify an AM-induced change in drought response; e.g., an AM effect on the decline in leaf or soil water potential required to cause stomatal closure disappeared when soils were salinized. Our findings confirm that AM fungi can alter host response to drought but do not lend much support to the idea that AM-induced salt resistance might help explain why AM plants can be more resilient to drought stress than their non-AM counterparts.

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Burri, S., P. Sturm, U. E. Prechsl, A. Knohl et N. Buchmann. « The impact of extreme summer drought on the short-term carbon coupling of photosynthesis to soil CO2 ; efflux in a temperate grassland ». Biogeosciences Discussions 10, n^o 7 (11 juillet 2013) : 11671–704. http://dx.doi.org/10.5194/bgd-10-11671-2013.

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Abstract. Along with predicted climate change, increased risks for summer drought are projected for Central Europe. However, large knowledge gaps exist in terms of how drought events influence the short-term ecosystem carbon cycle. Here, we present results from 13CO2 pulse labeling experiments at an intensively managed lowland grassland in Switzerland. We investigated the effect of extreme summer drought on the short-term coupling of freshly assimilated photosynthates in shoots to roots as well as to soil CO2 efflux. Summer drought was simulated using rainout shelters during two field seasons (2010 and 2011). Soil CO2 efflux and its isotopic composition were measured with custom-built chambers coupled to a quantum cascade laser spectrometer (QCLAS-ISO, Aerodyne Research Inc., MA, USA). During the 90 min pulse labeling experiments, we added 99.9 atom % 13CO2 to the grass sward. In addition to the isotopic analysis of soil CO2 efflux, this label was traced over 31 days into bulk shoots, roots and soil. Drought reduced the incorporation of recently fixed carbon into shoots and increased carbon allocation below-ground relative to total tracer uptake. Contrary to our hypothesis, we did not find a change in allocation speed in response to drought, although drought clearly reduced soil CO2 efflux rates. 19 days after pulse labeling, only about 60% of total tracer uptake was lost via soil CO2 efflux under drought compared to about 75% under control conditions. Predisposition of grassland by spring drought lead to different responses to summer drought in 2011 compared to 2010, suggesting increased sensitivity of grassland to consecutive drought events as predicted under future climate change.

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Gasaway, William C., Kathleen T. Gasaway et Hu H. Berry. « Persistent low densities of plains ungulates in Etosha National Park, Namibia : testing the food-regulating hypothesis ». Canadian Journal of Zoology 74, n^o 8 (1 août 1996) : 1556–72. http://dx.doi.org/10.1139/z96-170.

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Declines and persistent low densities of plains ungulates during 1960–1994 in Etosha National Park (Etosha) compromise Namibia's efforts to develop a wildlife- and tourist-based economy and maintain its national biodiversity. Plains ungulates are blue wildebeest (Connochaetes taurinus), plains zebra (Equus burchelli), springbok (Antidorcas marsupialis), and gemsbok (Oryx gazella). We tested the hypothesis that plains ungulate populations were well below their food-resource ceiling (FRC) and predicted that widely variable rainfall (food production) would have no significant effect on birth and survival rates; alternatively, ungulates regulated near their FRC would display strong responses to variable rainfall through negative feedback on fertility, yearling recruitment, and mortality. Data supported the hypothesis that Etosha's populations were well below their FRC. The pregnancy rate of springbok was high during drought. Recruitment of all four species was not positively related to rainfall. Mortality was not negatively related to rainfall, and high mortality did not occur during droughts. Given the high recruitment of Etosha's stable or declining populations, we hypothesize that high adult and yearling mortality resulting from anthrax and predation was the primary process preventing population growth. Management aimed at maintaining or increasing the numbers of Etosha's plains ungulates currently need not emphasize habitat enhancement.

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Hoekstra, N. J., J. A. Finn et A. Lüscher. « The effect of drought and interspecific interactions on the depth of water uptake in deep- and shallow-rooting grassland species as determined by δ18O natural abundance ». Biogeosciences Discussions 11, n^o 3 (15 mars 2014) : 4151–86. http://dx.doi.org/10.5194/bgd-11-4151-2014.

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Abstract. Increased incidence of weather drought, as predicted under climate change, has the potential to negatively affect grassland production. Compared to monocultures, vertical belowground niche complementarity between shallow- and deep-rooting species may be an important mechanism resulting in higher yields and higher resistance to drought in grassland mixtures. However, very little is known about the belowground responses in grassland systems and increased insight into these processes may yield important information both to predict the effect of future climate change and better design agricultural systems to cope with this. This study assessed the effect of a 10-week experimental summer drought on the depth of water uptake of two shallow-rooting species (Lolium perenne L. and Trifolium repens L.) and two deep-rooting species (Chicorium intybus L. and Trifolium pratense L.) in grassland monocultures and four-species-mixtures by using the natural abundance δ18O isotope method. We tested the following hypotheses: (1) drought results in a shift of water uptake to deeper soil layers, (2) deep-rooting species take up a higher proportion of water from deeper soil layers relative to shallow-rooting species, (3) as a result of interspecific interactions in mixtures, the water uptake of shallow-rooting species become shallower when grown together with deep-rooting species and vice versa, resulting in reduced niche overlap. The natural abundance δ18O technique provided novel insights into the depth of water uptake of deep- and shallow- rooting grassland species and revealed large shifts in response to drought and interspecific interactions. Compared to control conditions, drought reduced the proportional water uptake from 0–10 cm soil depth (PCWU0–10) of L. perenne, T. repens and C. intybus in monocultures by on average 54%. In contrast, the PCWU0–10 of T. pratense in monoculture increased by 44%, and only when grown in mixture did the PCWU0–10 of T. pratense decrease under drought conditions. In line with hypothesis 2, in monoculture, the PCWU0–10 of shallow-rooting species L. perenne and T. repens was 0.53 averaged over the two drought treatments, compared to 0.16 for the deep-rooting C. intybus. Surprisingly, in monoculture, water uptake by T. pratense was shallower than for the shallow-rooting species (PCWU0–10 = 0.68). Interspecific interactions in mixtures resulted in a shift in the depth of water uptake by the different species. As hypothesised, the shallow-rooting species L. perenne and T. repens tended to become shallower, and the deep-rooting T. pratense made a dramatic shift to deeper soil layers (reduction in PCWU0–10 of 58% on average) in mixture compared to monoculture. However, these shifts did not result in a reduction in the proportional similarity of the proportional water uptake from different soil depth intervals (niche overlap) in mixtures compared to monocultures. There was no clear link between interspecific differences in depth of water uptake and drought resistance. C. intybus, the species with water uptake from the deepest soil layers was one of the species most affected by drought. However, T. pratense, the species with the highest plasticity in depth of water uptake, was least affected by drought, suggesting an indirect effect of rooting depth on drought resistance. Our results show that niche complementarity in the depth of water uptake between shallow- and deep-rooting species may have contributed to the diversity effect in mixtures.

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Hubbard, Michelle, James J. Germida et Vladimir Vujanovic. « Fungal endophyte colonization coincides with altered DNA methylation in drought-stressed wheat seedlings ». Canadian Journal of Plant Science 94, n^o 2 (mars 2014) : 223–34. http://dx.doi.org/10.4141/cjps2012-111.

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Hubbard, M., Germida, J. J. and Vujanovic, V. 2014. Fungal endophyte colonization coincides with altered DNA methylation in drought-stressed wheat seedlings. Can. J. Plant Sci. 94: 223–234. Drought stress is one of the greatest limiting factors to Canadian agricultural production. The endophytic fungus SMCD 2206 improves wheat tolerance for drought. However, the mechanism(s) by which this mycobiont interacts with its host are not known. Methyl-sensitive amplified polymorphism (MSAP) was used to test the hypothesis that the endophyte colonization is associated with epigenetic modifications in drought-stressed wheat. Such epigenetic changes might be linked to elevated plant drought resistance. The DNA methylation patterns observed in drought-stressed wheat seedlings co-cultured with SMCD 2206 resembled those of unstressed controls (with or without the endophyte) much more closely than those of endophyte-free, drought-stressed plants. Consistent with the documented roles of transposable elements in plant epigenetics, DNA sequences isolated from some of the most prominent polymorphic MSAP bands were similar to a CACTA type transposon and two retrotransposons of Gypsy and Copia types. Another polymorphic band was similar to a wheat cytochrome p450 expressed sequence tag, suggesting that inoculation may be linked to altered plant responses to oxidative stress in drought conditions. These findings shed new light on the mechanisms involved in plant–endophyte associations, showing that SMCD 2206 colonization of wheat coincides with epigenetic differences in the plant host.

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Han, Bing, Di Cui, Xiaoding Ma, Guilan Cao, Hui Zhang, Hee Jong Koh et Longzhi Han. « Evidence for evolution and selection of drought-resistant genes based on high-throughput resequencing in weedy rice ». Journal of Experimental Botany 73, n^o 7 (18 février 2022) : 1949–62. http://dx.doi.org/10.1093/jxb/erab515.

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Abstract Weedy rice (Oryza sativa f. spontanea) is a relative of cultivated rice that propagates in paddy fields and has strong drought resistance. In this study, we used 501 rice accessions to reveal the selection mechanism of drought resistance in weedy rice through a combination of selection analysis, genome-wide association studies, gene knockout and overexpression analysis, and Ca2+ and K+ ion flux assays. The results showed that the weedy rice species investigated have gene introgression with cultivated rice, which is consistent with the hypothesis that weedy rice originated from de-domestication of cultivated rice. Regions related to tolerance have particularly diversified during de-domestication and three drought-tolerance genes were identified. Of these, Os01g0800500 was also identified using an assay of the degree of leaf withering under drought, and it was named as PAPH1, encoding a PAP family protein. The drought-resistance capacity of PAPH1-knockout lines was much lower than that of the wild type, while that of overexpression lines was much higher. Concentrations of Ca2+ and K+ were lower in the knockout lines and higher in the overexpression lines compared with those of the wild type, suggesting that PAPH1 plays important roles in coping with drought stress. Our study therefore provides new insights into the genetic mechanisms underlying adaptive tolerance to drought in wild rice and highlights potential new resistance genes for future breeding programs in cultivated rice.

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Florkiewicz, Aleksandra Bogumiła, Agata Kućko, Małgorzata Kapusta, Sebastian Burchardt, Tomasz Przywieczerski, Grażyna Czeszewska-Rosiak et Emilia Wilmowicz. « Drought Disrupts Auxin Localization in Abscission Zone and Modifies Cell Wall Structure Leading to Flower Separation in Yellow Lupine ». International Journal of Molecular Sciences 21, n^o 18 (18 septembre 2020) : 6848. http://dx.doi.org/10.3390/ijms21186848.

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Drought causes the excessive abscission of flowers in yellow lupine, leading to yield loss and serious economic consequences in agriculture. The structure that determines the time of flower shedding is the abscission zone (AZ). Its functioning depends on the undisturbed auxin movement from the flower to the stem. However, little is known about the mechanism guiding cell–cell adhesion directly in an AZ under water deficit. Therefore, here, we seek a fuller understanding of drought-dependent reactions and check the hypothesis that water limitation in soil disturbs the natural auxin balance within the AZ and, in this way, modifies the cell wall structure, leading to flower separation. Our strategy combined microscopic, biochemical, and chromatography approaches. We show that drought affects indole-3-acetic acid (IAA) distribution and evokes cellular changes, indicating AZ activation and flower abortion. Drought action was manifested by the accumulation of proline in the AZ. Moreover, cell wall-related modifications in response to drought are associated with reorganization of methylated homogalacturonans (HG) in the AZ, and upregulation of pectin methylesterase (PME) and polygalacturonase (PG)—enzymes responsible for pectin remodeling. Another symptom of stress action is the accumulation of hemicelluloses. Our data provide new insights into cell wall remodeling events during drought-induced flower abscission, which is relevant to control plant production.

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Lyubimova, Anna, Viktoriya Mamaeva et Anastasiya Menschikova. « Genetic drought resistance of modern oat varieties as a response to global climate change ». Agrarian Bulletin of the 221, n^o 06 (30 juin 2022) : 49–59. http://dx.doi.org/10.32417/1997-4868-2022-221-06-49-59.

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Abstract. Purpose. To assess the drought resistance of modern varieties of oats at the initial stage of ontogenesis by laboratory method. Methods. The following varieties of oats have been studied: Foma, Otrada, Talisman, Marshal, Ekspress, Assol’, Tigrovy and Petrovich. Relative drought resistance was determined by simulating drought by increasing the osmotic pressure with different concentrations of sucrose: 1.4; 4.4; 7.4; 10.5 and 16.6 %. This corresponded to osmotic pressures of 3, 6, 9, 12, and 18 atm. Distilled water was used as a control. The response of varieties to drought was determined by seed germination and depression of growth processes. Results. It was found that the varieties Talisman and Petrovich are characterized by very low resistance to drought – at an osmotic pressure of 3 atm, their germination was 29 and 52%, respectively. With a further increase in pressure, only single germinations with a very high degree of depression (more than 80%) were noted. Oat variety Ekspress was characterized by maximum resistance to drought. Its seeds germinated when the osmotic pressure increased to 12 atm (sucrose concentration reached 10.5 %). To a small extent, the Foma variety was inferior to it, which germinated worse than Ekspress, but had an average degree of depression of growth processes at an osmotic pressure of 3 to 12 atm. The rest of the studied oat varieties were moderately drought-resistant both in terms of germination and depression. Scientific novelty. The conducted analysis of variance showed that the relative drought resistance by 72 % depends on the concentration of sucrose, which indicates the inefficiency of the assessment by one concentration. The share of influence of a variety on genetically determined drought resistance is 10.3 %. This confirms the hypothesis that drought resistance is determined not only by genetic inheritance. It is recommended to use varieties Foma and Ekspress as parental forms in breeding for drought resistance.

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Burri, S., P. Sturm, U. E. Prechsl, A. Knohl et N. Buchmann. « The impact of extreme summer drought on the short-term carbon coupling of photosynthesis to soil CO2 ; efflux in a temperate grassland ». Biogeosciences 11, n^o 4 (20 février 2014) : 961–75. http://dx.doi.org/10.5194/bg-11-961-2014.

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Abstract. Along with predicted climate change, increased risks for summer drought are projected for Central Europe. However, large knowledge gaps exist in terms of how drought events influence the short-term ecosystem carbon cycle. Here, we present results from 13CO2 pulse labeling experiments at an intensively managed lowland grassland in Switzerland. We investigated the effect of extreme summer drought on the short-term coupling of freshly assimilated photosynthates in shoots to roots as well as to soil CO2 efflux. Summer drought was simulated using rainout shelters during two field seasons (2010 and 2011). Soil CO2 efflux and its isotopic composition were measured with custom-built chambers coupled to a quantum cascade laser spectrometer (QCLAS-ISO, Aerodyne Research Inc., MA, USA). During the 90 min pulse labeling experiments, we added 99.9 atom % 13CO2 to the grass sward. In addition to the isotopic analysis of soil CO2 efflux, this label was traced over 31 days into bulk shoots, roots and soil. Drought reduced the incorporation of recently fixed carbon into the shoots, but increased the relative allocation of fresh assimilates below ground compared to the control grasslands. Contrary to our hypothesis, we did not find a change of allocation speed in response to drought. Although drought clearly reduced soil CO2 efflux rates, about 75% of total tracer uptake in control plots was lost via soil CO2 efflux during 19 days after pulse labeling, compared to only about 60% under drought conditions. Thus, the short-term coupling of above- and below-ground processes was reduced in response to summer drought. The occurrence of a natural spring drought in 2011 lead to comparable albeit weaker drought responses increasing the confidence in the generalizability of our findings.

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López, Cristina María, Manuel Pineda et Josefa M. Alamillo. « Differential Regulation of Drought Responses in Two Phaseolus vulgaris Genotypes ». Plants 9, n^o 12 (21 décembre 2020) : 1815. http://dx.doi.org/10.3390/plants9121815.

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Drought is probably the most harmful stress affecting common bean crops. Domestication, worldwide spread and local farming practices has entailed the development of a wide variety of common bean genotypes with different degrees of resistance to water stress. In this work, physiological and molecular responses to water stress have been compared in two common bean accessions, PHA-0683 and PMB-0220, previously identified as highly and moderately resistant to water stress, respectively. Our hypothesis was that only quantitative differences in the expression patterns of key genes should be found if molecular mechanisms regulating drought resistance are similar in the two accessions. However, results presented here indicate that the resistance to drought in PMB-0220 and PHA-0683 common bean accessions is regulated by different molecular mechanisms. Differential regulation of ABA synthesis and ABA signaling related genes among the two genotypes, and the control of the drought-induced senescence have a relevant contribution to the higher resistance level of PHA-0683 accession. Our results also suggest that expression patterns of key senescence-related transcription factors could be considered in the screening for drought resistance in common bean germplasm collections.

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Ruíz, Magdalena, Miguel Quemada, Rosa M. García, José M. Carrillo et Elena Benavente. « Use of thermographic imaging to screen for drought-tolerant genotypes in Brachypodium distachyon ». Crop and Pasture Science 67, n^o 1 (2016) : 99. http://dx.doi.org/10.1071/cp15134.

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Thermal imaging has been used to evaluate the response to drought and warm temperatures in a collection of Brachypodium distachyon lines adapted to varied environmental conditions. Thermographic records were able to separate lines from contrasting rainfall regimes. Genotypes from dryer environments showed warmer leaves under water deficit, which suggested that decreased evapotranspiration was related to a more intense stomatal closure. When irrigated and under high temperature conditions, drought-adapted lines showed cooler leaves than lines from wetter zones. The consistent, inverse thermographic response of lines to water stress and heat validates the reliability of this method to assess drought tolerance in this model cereal. It additionally supports the hypothesis that stomatal-based mechanisms are involved in natural variation for drought tolerance in Brachypodium. The study further suggests that these mechanisms are not constitutive but likely related to a more efficient closing response to avoid dehydration in adapted genotypes. Higher leaf temperature under water deficit seems a dependable criterion of drought tolerance, not only in B. distachyon but also in the main cereal crops and related grasses where thermography can facilitate high-throughput preliminary screening of tolerant materials.

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PATTANAYAK, SUBHRENDU K., et RANDALL A. KRAMER. « Worth of watersheds : a producer surplus approach for valuing drought mitigation in Eastern Indonesia ». Environment and Development Economics 6, n^o 1 (15 janvier 2001) : 123–46. http://dx.doi.org/10.1017/s1355770x01000079.

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This study combines hydrological modeling with applied micro-econometric techniques to value a complex ecosystem service: drought mitigation provided by tropical forested watersheds to agrarian communities. Spatial variation in current baseflow allows estimation of drought mitigation values as the marginal profit accruing to agricultural households. The paper shows that this uncommon focus on producer (not consumer) surplus measures is appropriate for valuation as long as markets for commodities related to the environmental services are complete. For the typical household, the estimated marginal profit is positive, validating the central hypothesis that baseflow makes positive contributions to agricultural profits. There is some evidence, however, that increased watershed protection will increase profits through greater baseflow only in watersheds with a unique mix of physio-graphic and climatic features. The paper evaluates and provides some support for the hypothesis, put forward by hydrological science and the Indonesian Government, that protected watersheds can supply latent and unrecognized ecosystem services to local people.

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Friend, M. A., et G. E. Robards. « Staple strength of fine, medium and strong wool Merino wethers under drought conditions ». Australian Journal of Experimental Agriculture 46, n^o 9 (2006) : 1123. http://dx.doi.org/10.1071/ea05085.

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Fine, medium and strong wool Merino wethers (n = 72, 4 years old) were grazed together on drought-affected pastures in a semi-arid environment. In order to examine the hypothesis that restricting liveweight gains at the break of drought would improve staple strength, sheep were allocated to restricted grazing in a 5-ha paddock (drought group), or unrestricted grazing in a 20-ha paddock (drought-break group) when it was judged that the drought had broken in the region. Wool staples from all sheep broke at a point coinciding with summer rainfall events before allocation to treatment groups, and staple strength did not differ between treatments. Medium wool sheep (22.0 ± 1.6 N/ktex) produced wool of lower (P<0.001) staple strength than fine (30.0 ± 1.6 N/ktex) or strong (30.2 ± 1.6 N/ktex) wool sheep. Restricting the measurement of staple strength to the period when treatments were applied revealed no effect of treatment on staple strength, despite the fact that wethers in the drought-break group experienced a greater (P<0.001) liveweight gain (6.62 ± 0.37 kg) after allocation to their treatment than those in the drought group (–3.24 ± 0.37 kg). Staple strength was most strongly correlated with coefficient of variation of fibre diameter (r = –0.65; P<0.001); a result that was observed for all strains and treatment groups. The results indicate that coefficient of variation of fibre diameter is correlated with staple strength regardless of strain, and that management strategies designed to limit fibre diameter variability during a drought need to be applied not only at the break of a drought.

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Benwell, Andrew. « Response of rock-outcrop and fringing vegetation to disturbance by fire and drought ». Australian Journal of Botany 55, n^o 7 (2007) : 736. http://dx.doi.org/10.1071/bt07050.

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A comparative study of vegetation responses to fire and drought investigated whether species regeneration mode, seedling density response (SDR) and seedling shoot growth rate varied significantly in relation to disturbance agent (fire and drought), habitat type (rock-outcrop and fringing vegetation) and plant growth form. A three-way ANOVA showed that SDR varied significantly in relation to all three categorical variables and most strongly in relation to disturbance agent. Seeders comprised 87% of the post-fire flora and 99.3% of the peak seedling population in rock-outcrop habitat, while resprouters were much more prominent in fringing woodland. Species SDRs and seedling growth rates were generally much higher after fire. Fire produced a high SDR with high shrub, grass and ephemeral therophyte components, and drought produced a low SDR dominated by grasses and herbs and inhibited shrub and ephemeral recruitment. Post-fire obligate-seeder shrubs behaved as facultative resprouters after drought. Some species exhibited SDRs equivalent to fire and drought, others appeared to require fire for regeneration, while others recruited more successfully after drought. This spectrum of responses indicated a range of optimal disturbance environments, depending on species, which was only partly consistent with the hypothesis that species exhibit essentially the same life-history syndromes in response to fire and drought. The dominance of seeders in outcrop vegetation appeared to be related to skeletal soil, higher disturbance frequency and soil trophic conditions, rather than low fire frequency.

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Liu, Zhilei, Yuanjing Li, Lina Ma, Haichao Wei, Jianfeng Zhang, Xingyuan He et Chunjie Tian. « Coordinated Regulation of Arbuscular Mycorrhizal Fungi and Soybean MAPK Pathway Genes Improved Mycorrhizal Soybean Drought Tolerance ». Molecular Plant-Microbe Interactions® 28, n^o 4 (avril 2015) : 408–19. http://dx.doi.org/10.1094/mpmi-09-14-0251-r.

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Mitogen-activated protein kinase (MAPK) cascades play important roles in the stress response in both plants and microorganisms. The mycorrhizal symbiosis established between arbuscular mycorrhizal fungi (AMF) and plants can enhance plant drought tolerance, which might be closely related to the fungal MAPK response and the molecular dialogue between fungal and soybean MAPK cascades. To verify the above hypothesis, germinal Glomus intraradices (syn. Rhizophagus irregularis) spores and potted experiments were conducted. The results showed that AMF GiMAPKs with high homology with MAPKs from Saccharomyces cerevisiae had different gene expression patterns under different conditions (nitrogen starvation, abscisic acid treatment, and drought). Drought stress upregulated the levels of fungi and soybean MAPK transcripts in mycorrhizal soybean roots, indicating the possibility of a molecular dialogue between the two symbiotic sides of symbiosis and suggesting that they might cooperate to regulate the mycorrhizal soybean drought-stress response. Meanwhile, the changes in hydrogen peroxide, soluble sugar, and proline levels in mycorrhizal soybean as well as in the accelerated exchange of carbon and nitrogen in the symbionts were contributable to drought adaptation of the host plants. Thus, it can be preliminarily inferred that the interactions of MAPK signals on both sides, symbiotic fungus and plant, might regulate the response of symbiosis and, thus, improve the resistance of mycorrhizal soybean to drought stress.

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Schneider, Adam W., et Selim F. Adalı. « FURTHER EVIDENCE FOR A “LATE ASSYRIAN DRY PHASE” IN THE NEAR EAST DURING THE MID-TO-LATE SEVENTH CENTURY B.C. ? » Iraq 78 (27 octobre 2016) : 159–74. http://dx.doi.org/10.1017/irq.2016.5.

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In a recent paper published in the journal Climatic Change, we put forward the hypothesis that drought and overpopulation played an important, if indirect, role in shaping the sudden decline of the Assyrian Empire during the mid-to-late seventh century b.c. This argument was partly predicated on five paleoclimatic proxy records for conditions in different parts of the northern Near East during the first millennium b.c., each of which indicates that relatively arid conditions affected much of the region during the seventh century b.c., especially during its middle decades. Here, we revisit the textual and paleoclimatic proxy evidence for a period of drought in more depth to examine whether this evidence does in fact support the climatic component of our hypothesis. In this paper, we show that the available proxy evidence supports the notion that there was some kind of regional climatic perturbation that affected much of the Near East during the latter half of the seventh century b.c., which caused conditions in many parts of the region to become more arid. The strongest signal for this short-term episode of aridification, which we have termed the “Late Assyrian Dry Phase,” is observed at approximately 650–600 b.c. These proxies thus corroborate and provide the background for the Neo-Assyrian textual evidence for drought during the mid-seventh century b.c.

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McElrone, Andrew J., James L. Sherald et Irwin N. Forseth. « Effects of Water Stress on Symptomatology and Growth of Parthenocissus quinquefolia Infected by Xylella fastidiosa ». Plant Disease 85, n^o 11 (novembre 2001) : 1160–64. http://dx.doi.org/10.1094/pdis.2001.85.11.1160.

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A greenhouse study was conducted to test the hypothesis that bacterial leaf scorch symptoms, caused by Xylella fastidiosa, are more severe during periods of drought stress. A two-by-two complete factorial design with two pathogen treatments (control and infected) and two soil moisture levels (high and low) was used with Parthenocissus quinquefolia vines in 1999 and 2000. In each year, a high percentage of P. quinquefolia plants inoculated with X. fastidiosa expressed typical bacterial leaf scorch symptoms, with the outer scorched portion of the leaf separated from green tissue by a chlorotic halo. X. fastidiosa was detected in all symptomatic plants using an immunomagnetic capture and nested polymerase chain reaction technique, and was reisolated and cultured in modified periwinkle wilt liquid media. In both years, symptoms progressed further along the stem and were more severe at corresponding leaf positions in low-water-infected plants compared to high-water-infected plants. Total leaf area, shoot length, and number of nodes on the longest shoot per plant were all reduced due to drought and X. fastidiosa infection. This study is the first to verify the hypothesis that bacterial leaf scorch symptoms are enhanced during drought stress. Maintaining plant vigor with regular watering can be used to sustain plants infected by X. fastidiosa, particularly during periods of water stress.

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Herman, Jacob J., et Sonia E. Sultan. « DNA methylation mediates genetic variation for adaptive transgenerational plasticity ». Proceedings of the Royal Society B : Biological Sciences 283, n^o 1838 (14 septembre 2016) : 20160988. http://dx.doi.org/10.1098/rspb.2016.0988.

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Environmental stresses experienced by individual parents can influence offspring phenotypes in ways that enhance survival under similar conditions. Although such adaptive transgenerational plasticity is well documented, its transmission mechanisms are generally unknown. One possible mechanism is environmentally induced DNA methylation changes. We tested this hypothesis in the annual plant Polygonum persicaria , a species known to express adaptive transgenerational plasticity in response to parental drought stress. Replicate plants of 12 genetic lines (sampled from natural populations) were grown in dry versus moist soil. Their offspring were exposed to the demethylating agent zebularine or to control conditions during germination and then grown in dry soil. Under control germination conditions, the offspring of drought-stressed parents grew longer root systems and attained greater biomass compared with offspring of well-watered parents of the same genetic lines. Demethylation removed these adaptive developmental effects of parental drought, but did not significantly alter phenotypic expression in offspring of well-watered parents. The effect of demethylation on the expression of the parental drought effect varied among genetic lines. Differential seed provisioning did not contribute to the effect of parental drought on offspring phenotypes. These results demonstrate that DNA methylation can mediate adaptive, genotype-specific effects of parental stress on offspring phenotypes.

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Pryor, S. C., K. E. Hornsby et K. A. Novick. « Forest canopy interactions with nucleation mode particles ». Atmospheric Chemistry and Physics 14, n^o 21 (14 novembre 2014) : 11985–96. http://dx.doi.org/10.5194/acp-14-11985-2014.

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Abstract. Ultrafine particle size distributions through a deciduous forest canopy indicate that nucleation mode particle concentrations decline with depth into the canopy, such that number concentrations at the bottom of the canopy are an average of 16% lower than those at the top. However, growth rates of nucleation mode particles (diameters 6–30 nm) are invariant with height within the canopy, which implies that the semi-volatile gases contributing to their growth are comparatively well-mixed through the canopy. Growth rates of nucleation mode particles during a meteorological drought year (2012) were substantially lower than during a meteorologically normal year with high soil water potential (2013). This may reflect suppression of actual biogenic volatile organic compound (BVOC) emissions by drought and thus a reduction in the production of condensable products during the drought-affected vegetation season. This hypothesis is supported by evidence that growth rates during the normal year exhibit a positive correlation with emissions of BVOC modeled on observed forest composition, leaf area index, temperature and photosynthetically active radiation (PAR), but particle growth rates during the drought-affected vegetation season are not correlated with modeled BVOC emissions. These data thus provide indirect evidence that drought stress in forests may reduce BVOC emissions and limit growth of nucleation mode particles to climate-relevant sizes.

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Costa e Silva, Filipe, Alla Shvaleva, M. Helena Almeida, M. Manuela Chaves et João S. Pereira. « Responses to chilling of two Eucalyptus globulus clones with contrasting drought resistance ». Functional Plant Biology 34, n^o 9 (2007) : 793. http://dx.doi.org/10.1071/fp07080.

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The effect of chilling on growth and plant hydraulic properties in a drought-resistant clone (CN5) and a drought-sensitive clone (ST51) of Eucalyptus globulus Labill. was evaluated. Chilling (10/5°C, day/night) led to a general decrease in growth of both clones and significant reductions in root hydraulic conductivity, rate of photosynthesis and stomatal conductance in comparison to plants grown at control temperature (24/16°C). The drought-resistant CN5 clone maintained higher root growth and lower leaf-to-root-area ratio than the drought-sensitive ST51 clone, in both temperature treatments. Conversely, ST51 exhibited greater carbon allocation to the foliage and higher hydraulic conductance than clone CN5 at both temperatures. Plants of both clones, when acclimated to chilling, maintained a higher hydraulic conductivity than control plants exposed to chilling temperatures without acclimation. Under chilling, the main differences between clones were a higher water status and anthocyanin concentration in CN5 plants, and a stronger inhibition of root growth in ST51 plants. Except for roots, the hypothesis of a lower depression of growth rate in the drought-resistant clone under chilling was not verified. However, higher root growth under low temperatures, as observed in CN5, can be an advantageous trait in Mediterranean-type environments, protecting trees against summer water-stress.

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