Dissertations / Theses on the topic 'Ultramafic soils'

Ultramafic soils enriched in nickel, such as found in Australia and New Caledonia, are associated with unique, diverse and poorly known vegetation communities. Re-establishment of these highly specific ecosystems is still a challenge for Ni mining companies. Ultramafic vegetation communities are the outcome of a long evolution process resulting in their adaptation to the extreme soil conditions found on ultramafic outcrops. Mycorrhizal fungi, a very common plant symbiont, are generally thought to be beneficial to plants in other ecosystems, providing plants with phosphorus and even promoting metal tolerance in plants in some cases. We examined the hypothesis that mycorrhizal fungi may contribute to the survival of plants in ultramafic soil conditions. Bandalup Hill, an ultramafic outcrop enriched in Ni (South West of Western Australia) was selected to assess the contribution of mycorrhizal fungi to ultramafic plants. Soil constraints, in particular the degree of Ni toxicity, were assessed at two sites with ultramafic soils within the outcrop. Total metal, nutrient, DTPA extractable Ni and available P were measured in soil while Ni, Ca and Mg were tested in the soil solution. In addition, nutrients and metals were analyzed in shoots of some plant species occurring at each site: Eucalyptus flocktoniae, Melaleuca pomphostoma, Melaleuca coronicarpa and Hakea verucosa. Topsoils in Bandalup Hill and plant shoots had high levels of Ni, and very low levels of P, K and N. Variation in DTPA extractable Ni between sites reflected the variation in shoot Ni level of E. flocktoniae and M. pomphostoma. Variations in soil solution Ni levels reflected variations in shoot Ni levels of M. coronicarpa and H. verucosa between sites. The germination requirements of the plant species used to assess the soil constraints was assessed. Species selected included Eucalyptus flocktoniae, Melaleuca coronicarpa, and Hakea verucosa. Seeds of E. flocktoniae and M. coronicarpa had a higher germination rate if pre-treated with smoke water, while no pre-treatment was required to germinate H. verucosa seeds. The unusual germination requirement of E. flocktoniae and M. coronicarpa involve complex chemical signals that may be present in the soil when the conditions are more favorable for plant establishment. Such unusual germination requirement may represent an adaptation to the hostile conditions of the ultramafic soils of Bandalup Hill. The mycorrhizal association and root characteristics of the selected plant species was also assessed after 8 weeks of growth in undisturbed ultramafic topsoil cores from Bandalup Hill. Roots of these species (including H. verucosa from a previously designated non-mycorrhizal family, Proteaceae) were associated with mycorrhizal fungi. Roots of E. flocktoniae and M. coronicarpa were colonized by both arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (ECM), while roots of H. verucosa only contained some AM fungal structures. All species had high shoot to root ratios and their root characteristics reflected their association with mycorrhizal fungi. Based on the previous observations, uninoculated and inoculated E. flocktoniae seedlings were grown for 10 to 16 weeks in sand amended with Ni at 0, 0.2, 1 and 2.3 mg/kg. Mycorrhizal inoculum consisted of spores of Pisolithus sp. (ECM) or a mix of AMF spores and colonized root fragments, both originating from Bandalup Hill. Another inoculum consisted in Pisolithus sp. spores from a site with ultramafic soils in New Caledonia. Inoculation with AM and ECM fungi from Bandalup Hill was beneficial to E. flocktoniae. Benefits consisted mainly of a reduction of Ni shoot translocation at the highest Ni soil level. At 1 mg/kg soil Ni, E. flocktoniae exhibited a certain degree of tolerance to Ni. A substantial increase in growth and nutrient uptake with Pisolithus sp. from Western Australia was also observed. The contribution of AM fungi from Bandalup Hill to E. flocktoniae, M. coronicarpa, H. verucosa, and Trifolium subterraneum (clover) was then examined in ultramafic soil from Bandalup Hill.Steaming of ultramafic soil increased the availability and plant uptake of P. Consequently, uninoculated seedlings grew better, and inoculation with AM fungi decreased the growth of native plant species but did not affect their shoot Ni concentration. The presence of AM fungi increased the concentration of P in shoots of native plants species. Inoculation had no effect on the growth and nutrient content of subterranean clover. As mining activities have the potential to reduce the infectivity of AM fungi in topsoils, the effect of disturbance and storage practices on the AM infectivity of ultramafic topsoils collected in summer or winter from Bandalup Hill was investigated. Disturbance consisted in passing topsoil through a 2mm seive and cutting roots into 1cm fragments. Disturbed topsoil was then stored at room temperature in pots that were either sealed from the atmosphere or left open, and pots were maintained at field capacity. E. flocktoniae seedlings were planted in undisturbed and disturbed topsoil just after topsoil collect and then after 3, 6 and 9 months of topsoil storage. AM fungi present in the topsoil collected in summer was less susceptible to initial disturbance than AM fungi present in topsoil collected during winter. Also, storage of topsoil in sealed pots watered to field capacity was more detrimental to its infectivity than storage of topsoil in dry conditions. Mycorrhizal fungi can contribute to the survival of some native plant species in the ultramafic soils of Bandalup Hill and they may represent another strategy to improve the success of Ni mine revegetation. However, such contribution may not be the unique avenue for native plants to survive in ultramafic soils of Bandalup Hill.

High concentrations of potentially toxic elements (PTEs) in surface and near-surface environment may be attributed to both anthropogenic sources, including industrial and agricultural activity, and geogenic source, mainly due to natural weathering of rocks. Considering the geogenic sources, ultramafic rocks (e.g., dunite, peridotite, pyroxenite, and serpentinites) are among the most critical from the environmental point of view; in fact, they are characterized by high contents of Cr, Ni, Co, and other PTEs which can have potential harmful impact on ecosystems and human health if released into soils and waters during weathering and pedogenic processes. As a matter of the fact, weathering of ultramafic rock produces ultramafic soil containing high concentration of PTEs, including Cr, Ni, and Co compared to soils derived from non-ultramafic bedrock. Although ultramafic rocks and relative soils cover approximately 1% of the Earth’s surface, they are distributed worldwide and are commonly associated with ophiolite complexes; for this reason, they play an important role in environmental management. The main objective of this PhD thesis was to determinate the mineralogy and the chemistry of PTEs of ultramafic soil profiles from the Voltri Massif and to evaluate how lithological, textural, and structural properties of the ultramafic bedrock with various degree of serpentinization and deformation may affect the PTEs re-distribution and the fate in the soils during pedogenesis, as well as to assess their environmental implications in the ecosystem. The multidisciplinary and multiscale approach, used in this PhD thesis, has allowed to highlight a series of considerations that led to the following conclusions: • In the studied rocks, Cr, Ni, and, subordinately, Co are invariably the PTEs with the highest concentrations; in addition, V, Cu, and Zn are generally found in high concentrations. The main factors controlling the PTEs distribution within the studied ultramafic rocks appeared to be the serpentinization degree and the deformation style and intensity. The main source of the PTEs are spinel-group minerals. Moreover, PTEs-bearing phases are also represented by the other rock-forming minerals (such as serpentines, olivines, pyroxenes, and chlorites) and some accessory phases (e.g., ilmenite and other oxides, sulfides). • The studied ultramafic soil profiles vary in thickness from 35 to 80 cm and are characterized by weakly developed A and C horizons and a very thin O horizon (up to 5-10 cm). In general, in the soils the mineralogy of the skeleton (sandy and silty fractions) is closely related to bedrock mineralogy as expected for primitive A-C soils (in order of abundance: antigorite, chlorite, spinel-group minerals, pyroxenes, authigenic phases, quartz, olivine, and tremolite). The clay fraction is mainly composed by amorphous or low-crystalline Fe-oxyhydroxides, serpentines, smectite and illite/smectite mixed-layer clay, and clinochlore. Cr and Ni values have very variable concentrations over a wide range. Cr and Ni decrease according to serpentinization degree of bedrock. Co, Zn, and Cu do not show a clear correlation with bedrock serpentinization. V increase with the serpentinization of the bedrock. The PTEs concentrations in the studied ultramafic soil profiles are linked both to the primary minerals, inherited by bedrocks (e.g., serpentines, spinel-group minerals, pyroxenes, chlorites), and to their stable authigenic products (Fe-oxyhydroxides and clay minerals). The PTEs leached from the primary minerals is mainly scavenge by goethite, and subordinate by clay. • The results evidence that Cr, Ni, and, Co systematically exceed (up to one order of magnitude) the residential and industrial threshold values (CSC) according to Italian law (D.M. 471/1999; D.Lgs 152/2006) both in rocks and soils. However, combining all my results, I have demonstrated that the critical PTEs concentrations in the studied profiles have a geogenic origin and are linked both to the primary minerals, inherited by bedrocks, and to their stable authigenic products. Considering the high stability of authigenic products in supergenic environment, it is evident that this mineral species are effective and often permanent traps for the most important PTEs of ultramafic soils and bedrocks, thus reducing its bioavailability. A study of this kind that combine the bulk chemistry of outcropping rocks and the relative soil profiles with their geological, structural, mineralogical, and crystallochemical data, can be also a useful tool in environmental concerns to determine the PTEs distribution, to evaluate their potential mobility and bioavailability as well as to discriminate the natural geochemical background from possible source of contamination.

Thesis (PhD (Botany and Zoology)) -- University of Stellenbosch, 2006.
Metals are natural elements of the earth crust usually present at low concentrations in all soils. Although many metals such as cobalt, copper, iron and zinc are essential to living organisms, at elevated concentrations most metals are toxic to organisms living in and on soils. Elevated concentrations of metals are caused either by anthropogenic deposition following remobilisation from the earth crust or are of natural origin. Ultramafic soils do not only pose unfavourable living conditions such as drought and poor organic content, these soils are also characterized by extremely high concentrations of a range of metals known to be toxic under normal circumstances. Ultramafic soils are of high ecological importance as a high proportion of endemic organisms, especially plants, live on these soils. As it is known that earthworms do occur in ultramafic soils, the aims of the present study were to investigate the abilities of earthworms to survive in these soils and the influences of elevated chromium, cobalt, copper, manganese and nickel levels. For the evaluation of the metal background conditions, soils originating from ultramafic rocks of the Barberton Greenstone Belt, Mpumalanga, South Africa were collected and different fractions representing different levels of bioavailability were analyzed for arsenic, chromium, cobalt, copper, manganese and nickel. To assess the mobile, readily available metal fraction, i.e. Ca2+- exchangeable metal cations, a 0.01 mol/L CaCl2 extraction was performed. To investigate the mobilisable metal fraction, representing the amount of easily remobilisable complexed and carbonated metal ions, a DTPA (di-ethylene-triamine-pentaacetic acid) extraction was conducted. In relation to non-ultramafic or anthropogenic contaminated soils, a far lower proportion of metals were extractable by the above mentioned extraction methods. To investigate the availability and effects of these metals on earthworms, two ecophysiologically different species were employed. Aporrectodea caliginosa and Eisenia fetida were long-term exposed to the ultramafic soils collected at the Barberton region and a control soil from a location at Stellenbosch with a known history of no anthropogenic metal contamination. The responses to the ecological stress originating in the ultramafic soils were measured on different levels of earthworm organisation. As endpoints affecting population development, cocoon production, fecundity and viability were evaluated. On individual level, growth, metal body burden and tissue distribution were investigated. As endpoints on subcellular level, the membrane integrity was assessed by the neutral red retention assay, the mitochondrial activity was measured by the MTT colorimetric assay and as a biomarker for the DNA integrity, the comet assay was performed. Focussing on manganese and nickel, the uptake by E. fetida of these metals was investigated with the exclusion of soil related properties using an artificial aqueous medium to draw comparisons to the uptake of these metals in natural soils. The possible development of resistance towards nickel was tested by exposing pre-exposed (for more than 10 generations) E. fetida specimens to ultramafic soils with concentrations of more than 4000 mg/kg nickel. The results showed that, except on the endpoint survival, which was less sensitive than all other bioassays, significant responses to the ultramafic challenge were observed in all earthworm bioassays and on all levels of organisation. The sensitivity of the responses of the earthworms towards the ultramafic conditions was not predictable by the level of organisation. The two species showed different strategies of metal elimination. In A. caliginosa, metals such as nickel, manganese and chromium were transported to the posterior section and the posterior section was subsequently pushed off by autotomization. In E. fetida, metals such as chromium and nickel were sequestered in storage compartments in the coelomic cells or fluid. Other metals, such as cobalt, were not taken up at elevated concentrations. Although an increased accumulation of nickel was observed in E. fetida specimens pre-exposed to nickel, development of resistance or cross resistance was not observed in this species. In contrast, pre-exposed specimen exposed to elevated concentrations of nickel showed a higher sensitivity in terms of survival, indicating the absence of acclimatisation or even genetic adaptation. A comparison of the two species employed indicated that A. caliginosa was less suited for the assessment of the ultramafic soils due to the high individual variation in metal body burden, the mass loss observed and the slow reproduction rate even in the control soils. This happened despite the fact that A. caliginosa was a soil dwelling species supposed to be better adapted to the soil substrate than the litter dwelling E. fetida. The toxicity of the ultramafic soils was not necessarily related to total or environmentally available amounts of the selected metals. Thus, it can be speculated that either these soils contained unidentified toxicants with resulting interactions between toxicants playing an important role or earthworms were able to remobilize metals occurring in these soils. As the singular application of an ecotoxicological endpoint did not give reliable results, especially seen over the duration of the exposures, it can be concluded that, when studying soils with such a complex composition, the utilisation of endpoints addressing different levels of organisation is necessary for the assessment of toxic stress emerging from these ultramafic soils.

Exploration for chromitite-associated Pt deposits is hampered by a poor understanding of the distribution and behaviour of Pt in the surficial environment. This study investigates Pt content, residence sites and PGE mineralogy of soils developed on till and colluvium above the Tulameen ultramafic complex in southern British Columbia. Seventy-six soil profiles, as well as sediments, bogs and waters were sampled above the dunite core of the Tulameen complex, within which Pt occcurrences consist of massive-to-discontinuous segregations of platinic chromitite. Pt content of the -212 um fraction of soils and sediments was determined by fire assay-inductively coupled plasma spectroscopy. Samples from fourteen selected profiles were then examined in detail to determine Pt mineralogy and its distribution between different size, density and magnetic fractions. Pt concentrations in the -212 um fraction of C horizon soils range from 2 to 885 ppb and are closely related to soil dunite content, as estimated from MgO content and verified by XRD mineralogy. Dunite colluvium (mean: 24.2% MgO), locally-derived dunitic till (mean: 16.5% MgO) and exotic non-dunitic till (mean: 5.7% MgO) have median Pt concentrations of 88 ppb, 36 ppb and 8 ppb, respectively. This trend is evident in all size and density fractions. Pt content of heavy mineral (SG > 3.3) fractions is 10-2Ox greater than in light mineral fractions. Pt is most abundant in the heavy magnetic fraction from non-dunitic tills and dunitic tills remote from known mineralization, but the proportion of Pt in the heavy non-magnetic fraction increases with increasing proximity to mineralization. SEM and microprobe studies of heavy fractions from C horizons identified Pt-Fe-Cu alloys as free grains, and as inclusions in Mg-silicates and chromites. Chromite occurs as Mg-Cr-rich anhedral fragments and as Fe-rich euhedral to subhedral crystals. The latter, relatively more important in the magnetic fraction, are interpreted as Pt-poor grains disseminated throughout the dunite whereas fragments are relatively more important in the non-magnetic fraction and are interpreted as remnants of Pt-bearing massive chromitite segregations. The abundance of chromite fragments in soils near chromitite segregations accounts for the high Pt content of the non-magnetic heavy fractions of these soils. The -270 mesh fraction or the magnetic heavy fraction of C horizon soils would be the most suitable sample media for reconnaissance geochemical sampling. However, the greater contrast, more limited dispersion and Mg-Cr-rich chromite association of the non-magnetic heavy fraction make it a more suitable media for detailed geochemical sampling.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

La connaissance de la diversité microbienne des milieux ultramafiques est essentielle pour établir le fonctionnement écologique de ces milieux, qui présentent de fortes teneurs en Ni et sont caractérisés par une flore particulière, e.g. plantes hyperaccumulatrices de Ni. La rhizosphère des hyperaccumulateurs comporte une forte proportion de bactéries résistantes au Ni, qui peuvent aussi agir sur la nutrition des plantes et sur les propriétés physico-chimiques du sol. Le premier défi de cette thèse a été de cerner le déterminisme de la diversité bactérienne de la rhizosphère d’hyperaccumulateurs de Ni. Le second a été de tester l'intérêt de souches PGPR (Plant Growth Promoting Rhizobacteria) pour optimiser l'agromine à partir d'interactions entre les rhizobactéries et les hyperaccumulateurs de Ni. La démarche s'est appuyée sur un ensemble de prospections dans deux régions climatiques et sur des analyses de séquençage haut débit. Des tests de cultures de plantes hyperaccumulatrices inoculées ont également été conduits. Les résultats montrent que le déterminisme de la diversité bactérienne est variable selon l'échelle spatiale. A l'échelle mondiale, le type de végétation est le facteur majeur structurant les communautés bactériennes, elle-même contrôlée indirectement par le climat. L’influence directe du climat (température et humidité) sur la diversité est significative mais moindre. A l'échelle d'une région climatique, la physico-chimie des sols ultramafiques structure et détermine la diversité des communautés bactériennes rhizosphériques. Enfin, l'inoculation de souches PGPR fortement bioaccumulatrices de Ni modifie la dynamique du Ni dans le sol, ce qui démontre qu'il existe une compétition pour le Ni entre la plante et la bactérie inoculée. En conclusion, le déterminisme de la diversité des communautés bactériennes rhizosphériques est dépendant de l'échelle spatiale considérée. En outre, le choix de la souche PGPR à inoculer, dans un contexte d'amélioration de l'agromine du Ni, est primordial
Knowledge of the microbial diversity in ultramafic areas is essential to establish the ecological functioning of these environments, which display high level of Ni and are characterized by the presence of particular plants, e.g. Ni hyperaccumulators. The rhizosphere of these plants promotes a high proportion of Ni resistant bacteria that can act on plant nutrition and soil physicochemical properties. The first challenge of this thesis was to understand the bacterial rhizosphere diversity of Ni hyperaccumulators. The second was to test the interest of PGPR (Plant Growth Promoting Rhizobacteria) strains in order to improve agromining based on rhizobacteria and Ni hyperaccumulators interactions. The approach was based on two-contrasted climatic areas prospection and on high-throughput sequencing analyzes. Tests on culture of hyperaccumulator plants inoculated were also conducted. The results show that the determinism of this bacterial diversity is variable according to the spatial scale. On a global scale, the vegetation type, indirectly influenced by the climate, is the major factor structuring bacterial communities. The direct influence of the climate (temperature and humidity) on bacterial diversity is significant but lower. At the scale of a climatic region, the physic-chemistry of ultramafic soils structures and determines the rhizosphere bacterial community diversity. Finally, the inoculation of highly Ni bioaccumulative PGPR strains modifies the Ni dynamic in the soil, demonstrating that there is a competition for this metal between the inoculated bacteria and the hyperaccumulator plant. In conclusion, the rhizosphere bacterial community diversity is dependent on the considered spatial scale. Furthermore, these results emphasize how the choice of the PGPR strain to inoculate is important in order to improve Ni agromining

La connaissance de la diversité microbienne des milieux ultramafiques est essentielle pour établir le fonctionnement écologique de ces milieux, qui présentent de fortes teneurs en Ni et sont caractérisés par une flore particulière, e.g. plantes hyperaccumulatrices de Ni. La rhizosphère des hyperaccumulateurs comporte une forte proportion de bactéries résistantes au Ni, qui peuvent aussi agir sur la nutrition des plantes et sur les propriétés physico-chimiques du sol. Le premier défi de cette thèse a été de cerner le déterminisme de la diversité bactérienne de la rhizosphère d’hyperaccumulateurs de Ni. Le second a été de tester l'intérêt de souches PGPR (Plant Growth Promoting Rhizobacteria) pour optimiser l'agromine à partir d'interactions entre les rhizobactéries et les hyperaccumulateurs de Ni. La démarche s'est appuyée sur un ensemble de prospections dans deux régions climatiques et sur des analyses de séquençage haut débit. Des tests de cultures de plantes hyperaccumulatrices inoculées ont également été conduits. Les résultats montrent que le déterminisme de la diversité bactérienne est variable selon l'échelle spatiale. A l'échelle mondiale, le type de végétation est le facteur majeur structurant les communautés bactériennes, elle-même contrôlée indirectement par le climat. L’influence directe du climat (température et humidité) sur la diversité est significative mais moindre. A l'échelle d'une région climatique, la physico-chimie des sols ultramafiques structure et détermine la diversité des communautés bactériennes rhizosphériques. Enfin, l'inoculation de souches PGPR fortement bioaccumulatrices de Ni modifie la dynamique du Ni dans le sol, ce qui démontre qu'il existe une compétition pour le Ni entre la plante et la bactérie inoculée. En conclusion, le déterminisme de la diversité des communautés bactériennes rhizosphériques est dépendant de l'échelle spatiale considérée. En outre, le choix de la souche PGPR à inoculer, dans un contexte d'amélioration de l'agromine du Ni, est primordial
Knowledge of the microbial diversity in ultramafic areas is essential to establish the ecological functioning of these environments, which display high level of Ni and are characterized by the presence of particular plants, e.g. Ni hyperaccumulators. The rhizosphere of these plants promotes a high proportion of Ni resistant bacteria that can act on plant nutrition and soil physicochemical properties. The first challenge of this thesis was to understand the bacterial rhizosphere diversity of Ni hyperaccumulators. The second was to test the interest of PGPR (Plant Growth Promoting Rhizobacteria) strains in order to improve agromining based on rhizobacteria and Ni hyperaccumulators interactions. The approach was based on two-contrasted climatic areas prospection and on high-throughput sequencing analyzes. Tests on culture of hyperaccumulator plants inoculated were also conducted. The results show that the determinism of this bacterial diversity is variable according to the spatial scale. On a global scale, the vegetation type, indirectly influenced by the climate, is the major factor structuring bacterial communities. The direct influence of the climate (temperature and humidity) on bacterial diversity is significant but lower. At the scale of a climatic region, the physic-chemistry of ultramafic soils structures and determines the rhizosphere bacterial community diversity. Finally, the inoculation of highly Ni bioaccumulative PGPR strains modifies the Ni dynamic in the soil, demonstrating that there is a competition for this metal between the inoculated bacteria and the hyperaccumulator plant. In conclusion, the rhizosphere bacterial community diversity is dependent on the considered spatial scale. Furthermore, these results emphasize how the choice of the PGPR strain to inoculate is important in order to improve Ni agromining

Un tiers de la surface de la Nouvelle-Calédonie est recouvert par des massifs ultramafiques caractérisés par des conditions édaphiques extrêmes contribuant au développement d’une flore unique. L'interaction avec les microorganismes du sol et notamment les rhizobactéries constitue une adaptation essentielle chez ces plantes. C'est dans ce contexte que s'insère cette thèse dont l'objectif est de comprendre le rôle de ces rhizobactéries dans l'adaptation des plantes à la contrainte édaphique. Cette thèse s'intéresse plus particulièrement aux bactéries appartenant au genre Burkholderia et Curtobacterium isolées des sols ultramafiques de Nouvelle-Calédonie. Ce travail a été scindé en trois objectifs : (1) Caractériser les isolats bactériens, (2) Evaluer la réponse adpatative des bactéries à la contrainte édaphique et (3) Evaluer l'action promotrice de la croissance des plantes. Ce travail a permis de mettre en évidence l'existence des taxons bactériens originaux inféodés aux sols ultramafiques avec des mécanismes particuliers impliqués dans la tolérance aux métaux et jouant un rôle majeur dans l'adaptation des plantes à la contrainte édaphique. Des essais de co-inoculation avec des champignons mycorhiziens à arbuscules ont montré des effets bénéfiques sur la mise en place de la symbiose mycorhizienne entraînant une amélioration de la croissance des plantes. D'un point de vue appliqué, les résultats de ce travail de thèse ont permis de montrer que l'interaction de ces rhizobactéries avec les champignons mycorhiziens à arbuscules constitue une voie prometteuse pour la restauration des sites miniers dégradés de Nouvelle-Calédonie
In New caledoia, a tropical archipelago in the South Pacific Ocean, one third of the main island is covered by ultramafic solis that contribute to the development of a unique flora. Interaction with soils microorganisms, particularly rhizobacteria, is an essential adaptation in plants found on ultramafic soils. The objective of this thesis is to understand the role of these rhizobacteria isolated from New Caledonia ultramafic soils in the adpatation of plants to soils constraints. This thesis focuses on bacteria belonging to the genera Burkholdelria and Curtobacterium isolated from New Caledonian ultramafic soils. This work is divided into three objectives, (1) The characterization of the bacterial isolates, (2) The Evaluation of the adaptive response of bacteria to metal stress and (3) The evaluation of the plant growth promoting effect. This work highlights the existence of original taxa subordinated to ultramafic soils with particular mechanisms of resistance to metals involving in the adapatation of plants to soils stress. Mechanisms of resistance to metals depending on the bacterial species considered have been identified and are responsible of alleviation of metal in plants. Co-inoculation trials with arbuscular mycorrhizal fungi have shown beneficial effects on the development of mycorrhizal improving the plant growth. In addiction, the results obtained make interesting conclusions on the adpatation of plant species in ultramafic soils for improving ecological restoration program. Moreover, the interaction of the rhizobacteria with arbuscular mycorrhizal fungi seems to be a promising way to restore degraded mining sites in New Caledonia

L'hyperaccumulation est un phénomène qui a été découvert il y a 45 ans seulement, il a fait l'objet de nombreuses recherches, en raison du comportement inhabituel des métaux dans l'écosystème et en raison du potentiel de solutions fondées sur la nature qui en découle. La description du cycle biogéochimique du Ni des plantes hyperaccumulatrices est nécessaire pour élucider leur rôle écologique dans leur environnement naturel, mais aussi pour comprendre leur comportement potentiel dans des cultures tropicales d’agromine. L'exploitation agricole et l'exportation de la biomasse riche en Ni interrompront le cycle du Ni. Il est donc important de comprendre les mécanismes qui régissent le cycle biogéochimique du Ni dans les systèmes naturels et de cultures : Quels sont les cycles du Ni et leur impact sur le fonctionnement écologique des forêts tropicales d’hyperaccumulateurs ? Quelle est la vitesse des flux de Ni à travers les compartiments sol-plante et quelle est la dynamique et le renouvellement du Ni dans un système tropical d'hyperaccumulateurs ? À quelle vitesse une culture tropicale Agromine peut-elle épuiser le Ni dans le sol ? Comment pouvons-nous gérer la fertilisation des sols pour une culture d’agromine tropicale de Ni durable ? Les objectifs de ce doctorat étaient donc les suivants (i) d'étudier le cycle biogéochimique d'une forêt naturelle de Phyllanthus rufuschaneyi afin d'évaluer les flux de Ni dans l'écosystème ; (ii) de manipuler un tel écosystème afin d'effectuer un test de sensibilité de l'écosystème pour le flux suivant : retour de la litière au sol ; de l'absence de retour (exportation) à un doublement du retour ; (iii) d'optimiser le système de culture de P. rufuschaneyi pour l'agromine du Ni. Deux peuplements parallèles de P. rufuschaneyi ont été instrumentés, surveillés et comparés pendant deux ans (2018 et 2019), (i) une forêt secondaire naturelle de 100 m2 et (ii) un champ densément planté dans lequel les retours de litière au sol ont été calibrés ; de l'absence de retour (exportation) à un doublement du retour. Cette étude n'a pas révélé l'allopathie des plantes hyperaccumulatrices tropicales. Les plantes hyperaccumulatrices de Ni influent sur la constitution des stocks de Ni disponibles dans les couches arables. Le cycle du Ni est principalement régi par des flux internes, notamment la dégradation et le recyclage de la litière. Ce pourcentage de renouvellement du Ni ne semble pas être influencé par le taillis à court terme mais par la présence initiale de litière sur le sol. La fertilisation NPK n'a aucun effet sur le rendement en Ni à court terme (75 kg Ni ha-1 an-1), même si la fertilisation en azote a tendance à réduire le rendement en Ni de P. rufuschaneyi. Il convient de tenir compte du renouvellement du nickel lors de la conception des cultures d’agromine tropicales. Une étude plus approfondie de l’altération permettrait de préciser son rôle dans la reconstitution des stocks de Ni disponible et de nutriments
Hyperaccumulation is a phenomenon that was only discovered 45 years ago, it has been the focused of very intensive research because of the unusual behaviour of metals in the ecosystem and also because it offers a vast potential for nature-based solutions. Describing the Ni biogeochemical cycle within the soil-hyperaccumulator plants ecosystem is necessary to elucidate the ecological role of hyperaccumulator plants in their natural environment, but also to understand their potential behaviour under tropical agromining systems. Agromining and exporting Ni rich-biomass will interrupt the cycle. It is therefore important to understand the mechanisms which govern the Ni biogeochemical cycle in both natural and agromining systems: What are the Ni cycles (internal and external) and their impact on the ecological functioning of tropical hyperaccumulator forest? How rapid are the Ni fluxes across the soil-plant compartments, and what is the turnover of Ni in a hyperaccumulator tropical system? How fast can a tropical Agromining crop deplete Ni in soil? How can we manage soil fertilisation for a sustainable tropical Ni agromining crop? Therefore, the objectives were: (i) to study the biogeochemical cycling of a natural forest of Phyllanthus rufuschaneyi in order to assess and evaluate the natural fluxes of Ni in the ecosystem; (ii) to manipulate such an ecosystem in order to perform a sensitivity test of the ecosystem for the following flux: litter return to the soil; (iii) to optimize the cropping system of P. rufuschaneyi for Ni agromining. Two parallel stands of P. rufuschaneyi were instrumented, monitored and compared over two years (2018 and 2019), (i) a natural secondary 100-m2 forest and (ii) a densely planted field in which litter returns to the soil were calibrated; from no return (export) to a doubling of the return.This study did not prove allelopathy of tropical hyperaccumulator plants, despite the extreme influence of Ni hyperaccumulators in building up available Ni stocks in topsoils. Nickel cycle was mainly driven by internal fluxes, i.e. degradation and recycling of the hyperaccumulator biomass. The percentage of Ni recycled by litterfall tended to decrease with increasing litter addition to the soil and was not influenced by coppicing, at least in the short term. Major nutrient (NPK) fertilisation did not affect Ni yield (i.e. 75kg Ni ha-1 yr-1) in the short term either, even if N fertilisation reduced Ni concentrations in leaves and plant biomass production. Nickel turnover should be taken into account when designing tropical agromining crops and natural secondary forests are a good surrogate to evaluate the long term impacts of agromining. Further study of the weathering processes would help to precise the contribution of bedrock and soil mineral horizons in the Ni and nutrient budgets of the system

Une solution pour stabiliser les résidus d’extraction minière de latérites nickélifères est de les végétaliser avec des plantes natives de ces sols ultramafiques. L’objectif de cette thèse était d’étudier la réactivité géochimique des stériles miniers nickélifères des massifs de Niquelândia et Barro Alto (Goiás) dans l’optique de mettre en œuvre ce procédé de revégétalisation.La minéralogie et la réactivité des phases porteuses d’ETM dans les stériles ont été déterminées. L’influence du transport et de la composition de la solution au contact du stérile sur la mobilisation du Ni ont ensuite été étudiées par des expériences en colonne saturée et insaturée. Enfin, la comparaison de la composition de la solution circulant dans les sols naturels ultramafiques avec celle circulant dans des parcelles expérimentales de minerais types a permis d’obtenir une première évaluation de l’adaptabilité des plantes aux stériles.Deux phases majeures sont présentes dans les stériles : un matériau garniéritique, principalement composé de smectites ferrifères riches en Ni échangeable (1230 mg kg-1) ; et un matériau limonitique, principalement composé de goethite, pauvre en nickel mobile, mais riche en Cr(VI) échangeable (980 mg kg-1) complexé en sphère interne à la surface des goethites. Goethite et smectite ont servi de modèles pour affiner la détermination des mécanismes impliqués dans la mobilisation du nickel (modélisation PHREEQC). Outre les réactions de complexation de sphère externe et interne cette étude montre que la dissolution des phases minérales (phyllosilicates, oxydes de fer et de manganèse) et l’adsorption des complexes métal-(citrate/EDTA) jouent un rôle important dans la composition de la solution dans les stériles
A way to ensure physical and chemical stability of mining spoils heaps from nickeliferous laterites is to revegetate them using the native vegetation of the ultramafic soils. The aim of this work was to study the geochemical reactivity of nickeliferous mining spoils of Niquelândia and Barro Alto complexes (Goiás) for the further application of such a revegetation process. Mineralogy and reactivity of TME bearing phases in the spoils were determined. The influence of transport and percolating solution composition on the Ni mobilisation were then studied using saturated and unsaturated column experiments. Finally, the comparison of the composition of solution circulating in natural ultramafic soils with those circulating in experimental plots composed of typical mining ores allowed us to have a first evaluation of the adaptability of natural vegetation to spoils. Two main phases are present in the spoils: a garnieritic spoil, mainly composed of ferruginous smectites enriched in exchangeable Ni (1230 mg kg-1); and a limonitic spoil, mainly composed of goethite with little mobile Ni but very high exchangeable Cr(VI) contents (980 mg kg-1) located as outer sphere complexes at the goethite surface. Synthetic goethite and purified smectite served as model phases to refine the characterisation of main reactive mechanisms implied in Ni mobilisation (PHREEQC modelling). Besides outer (smectite, garnierite) and inner (goethite, limonite) sphere complexation reactions, we showed that the dissolution of mineral phases (phylosilicates, goethite and manganese oxides) and the adsorption of metal-citrate or metal-EDTA complexes do have an important role in the composition of the solution circulating in the spoils

Le « topsoil » comme outil de restauration écologique des terrains miniers dégradés, consiste à récupérer la couche de sol naturellement riche en matières organiques, semences et micro-organismes (qui définissent le potentiel biologique de restauration), lors d'une opération qui précède l'exploitation minière, puis à l'épandre sur les sites à restaurer. Au coeur desproblématiques de restauration écologique, les topsoils apparaissent à travers la littérature comme une technique efficiente et leur utilisation est abondamment préconisée. Toutefois celle-ci ne date, en Nouvelle-Calédonie, que des années 2000. Les connaissances actuelles locales liées à cet outil sont encore fragmentaires, et les caractéristiques des topsoils, tout comme les résultats obtenus sont hétérogènes. Ce travail de recherche a permis d'améliorer notre compréhension des interactions entre les composantes biologiques des topsoils et les phénomènes intervenant dansleur évolution (banque de graines, micro-organismes, et caractéristiques physico-chimiques). Les résultats obtenus ont montré que l'utilisation des topsoils en restauration écologique peut favoriser la restauration des écosystèmes ultramafiques néo-calédoniens, et pourraient trouver une application dans la conception de nouvelles stratégies de restauration écologiques des terrains miniers dégradés du territoire. Néanmoins, il est également apparu que les topsoils ne peuvent à eux seuls restaurer la totalité de la diversité végétale qui caractérise les substrats ultramafiques du territoire, et doivent donc être associés à d'autres techniques de restauration
"Topsoil", as an ecological tool of restoration of the mines made in terraces, consist of getting back the layers full of organic matter, seeds and micro-organisms (which define the biological potential of restoration), during a procedure made following the exploitation of the mines, then could be extend to the sites which require some restoration.While the problem of ecological restoration is at the center of the debate, topsoil appears, according to the literature, as an efficient technique and their uses are well recommended. However, they only have been used in New Caledonia since the beginning of the XXI century. The actual knowledge of this specific tool is still incomplete, and the characteristics of topsoil, same as the results, remain inconsistent. The research made around this topic gave us a better understanding of the interaction between the biological components of topsoil and their way of evolving (seeds’ bank, micro-organisms and the physic and chemical characteristics). The results obtained demonstrate that the use of topsoil as an ecological restoration could be beneficial for the restoration of the ultramafic ecosystem of New Caledonia. It could, as well, find a place in the development of new strategies of ecological restoration of mines in terrace of the country. However, it has been shown in another hand that topsoil would not be sufficient to restore the entire vegetal diversity of the ultramafic bedrock of the country. For this reason, it has to be associated with different techniques of restoration

Les terrains ultramafiques de Nouvelle-Calédonie, riches en Ni, Co, Mn et Cr sont exploités par des mines à ciel ouvert, ce qui génère l'émission de poussières riches en métaux. L'objectif de ce travail est de développer des approches pour estimer le risque environnemental lié aux poussières émises par les mines à ciel ouvert et les usines de traitement du minerai de nickel. L'estimation de la fraction biodisponible des métaux contenus dans deux fractions granulométriques de poussières, celle inférieure à 100 ~m mobilisable par le vent (F<1 OO~m.) et celle susceptible de pénétrer le système respiratoire (PM1 0), a été réalisée par extractions cinétiques à I'EDTA. L'obtention des PM10 a nécessité la mise au point d'une technique de tri par transport des particules dans un tube horizontal grâce à un flux d'azote. Les extractions cinétiques ont permis de discrimtner trois fractions de métaux: rapidement extraite, lentement extraite et non biodisponibles. Les concentrations en métaux potentiellement biodisponibles sont toujours très élevées et la fraction lentement extraite est toujours la plus concentrée. Pour F<1 00 ~m. les constantes cinétiques de la fraction lentement extraite sont plus faibles pour les poussières de sols miniers que celles de sols forestiers. Les poussières issues de sols miniers seraient alors un réservoir en éléments métalliques biodisponibles à plus long terme. La bioindication lichénique avec traitement en données compositionnelles des concentrations en métaux permet de définir un indice de dispersion des poussières. Cette méthodologie pourrait appuyer les réseaux de surveillance de la qualité de l'air en Nouvelle-Calédonie
Bioavailability estimation of nickel, cobalt and manganese in dust from ultramafic soils likely to be mobilized by wind and~eve lopment of a bioindication tool using lichen for dust emitted by mining activities in New Caledonia New Caledonian altered ultramafic soils, particularly rich in Ni, Co, Mn and Cr, are extracted by opencast mines which generale dust rich in metals. The objective of th is work is to develop approaches for environmental risk assessment of dust emitted by opencast mines and nickel ore metallurgical plants. The assessmentof metals' bioavailable fraction from two dust granulometrie size fractions, one less than 100 IJm which is mobilizable by wind (F<1001Jm,) and another one able to penetrate the respiratory system (PM 1 0), has been determined by kinetic extraction with EDT A. The development of a new separation deviee based on particle transport subjected to a nitrogen flux in a horizontal tube has been necessary for PM1 0 segregation. Kinetic extractions le ad to the distinction of th ree metal pools: rapidly labile, less rapidly labile and non-bioavailable. Trace metal potentially bioavailable concentrations were always high and the less rapidly labile pool is always the most concentrated pool. Concerning F<1 001Jm, the less rapidly kinetic constant of the less rapidly labile pool is weaker for mining soils than forest soils. F<1001Jm fractions from mining soils representa more durable reserve in trace metal than the same fraction from forest soils. Bioindication using lichens with compositional data analysis of their metal concentration allow defining an indicator of emission dispersion. This methodology could support air quality monitoring networks in New Caledonia

Une des solutions les plus prometteuses pour la restauration écologique des milieux dégradés, mais aussi pour l’agriculture, est l’utilisation des champignons mycorhiziens à arbuscules (CMA). En effet, ces champignons permettent de conférer aux plantes une meilleure nutrition minérale et une tolérance aux stress biotiques et abiotiques du milieu. L’étude réalisée ici part de l’hypothèse que les effets simultanés de plusieurs CMA taxonomiquement bien différents pourraient permettre de réduire la majorité des contraintes et permettre ainsi à la plante de s’adapter et se développer de façon optimale dans les sols extrêmes (ultramafiques) dégradés par l’activité minière. Les objectifs de cette thèse sont de caractériser les CMA isolés de ces milieux ultramafiques d’un point de vue taxonomique et fonctionnel (croissance et d’adaptation de la plante hôte). Ce travail a permis la découverte de cinq espèces nouvelles de CMA (Błaszkowski et al. 2017 ; Crossay et al. 2018). La complexité des méthodes d’identification de ces symbiotes, a suscité une réflexion scientifique qui a permis d’aboutir à la mise au point d’une méthode d’identification par MALDI-TOF MS précise et routinière pour l’identification des CMA (Crossay et al. 2017). Les différents isolats identifiés et cultivés en laboratoire ont ensuite été testés en conditions expérimentales afin d’évaluer leurs fonctions individuelles et collectives au sein des plantes hôtes (Crossay et al. 2019). En conclusion, la co-inoculation de ces différentes nouvelles espèces de CMA natives des sols ultramafiques de Nouvelle-Calédonie permet une grande amélioration de la croissance des plantes et de leur adaptation à ces milieux extrêmes
Plant arbuscular mycorrhizal fungi (AMF) symbiosis can be critically important in the development of sustainable agriculture, remediation of polluted lands and ecological restoration of degraded sites, such as mines. Indeed, AMF symbioses improve plant growth and tolerance to biotic and abiotic stresses from the environment. This study based on the hypothesis, that in environments facing different stress factors, inoculation with several species from different AMF taxa may be essential to promote growth and to withstand stresses of plant in ultramafic soils of mine-degraded areas. The aims of the present study were to characterize taxonomically (isolate, describe, and identify) and functionally (plant growth and adaptation) AMF from ultramafic soil. Five new species of AMF from ultramafic soil were described (Blaszkowski et al. 2017; Crossay et al. 2018). Taxonomic identification of AMF need considerable expertise and is not well-adapted for “routine” identification. Therefore, we developed a fast, accurate and efficient method for AMF identification using MALDI-TOF MS proteomic-based biotyping approach (Crossay et al. 2017). Finally, we analyzed the effects of six species of AMF from a New Caledonian ultramafic soil on plant growth and nutrition, using mono-inoculations and mixtures comprising different numbers of AMF species, in a greenhouse experiment. Our results suggest that, co-inoculation of native AMF was very efficient in improving growth and tolerance to heavy metals of plants in ultramafic soil (Crossay et al. 2019)

Les écosystèmes forestiers tropicaux représentent près de la moitié de la superficie forestière mondiale. Ces écosystèmes qui fournissent des services fondamentaux pour le bien-être de nos sociétés (e.g. régulation des flux de matières, maintien des sols) sont particulièrement touchés (perte et dégradation des forêts) par les changements globaux. La Nouvelle‐Calédonie, et ses substrats ultramafiques, ne font pas exception à cette tendance. L’activité minière et les feux sont responsables de la régression, de la fragmentation, de la dégradation des forêts et de l’érosion des sols. L’archipel est classé parmi les points chauds de la biodiversité mondiale et la restauration écologique de ces écosystèmes revêt de forts enjeux. L’objectif appliqué de cette thèse est de contribuer à la restauration écologique des forêts de NouvelleCalédonie afin de limiter l’érosion des sols sur substrats ultramafiques, et s’inscrit dans le champ disciplinaire de l’écologie de la restauration. L’objectif scientifique est d’étudier l’influence des symbioses mycorhiziennes et des traits racinaires sur l’érosion des Ferralsols développés sur substrats ultramafiques à travers une approche multi-échelle. Dans la première partie, nous mettons en évidence les caractéristiques floristiques et structurales de communautés végétales sur substrats ultramafiques. Celles-ci laissent présager une expression accrue des traits racinaires des espèces dominantes dans les forêts monodominantes. La place centrale du feu et des cyclones dans la dynamique de succession végétale est également soulignée, tout comme celle des symbioses mycorhiziennes dans le maintien de la monodominance de Nothofagus aequilateralis. Dans la deuxième partie, notre travail permet de suggérer l’existence d’un seuil biotique entre les maquis lignoherbacés dégradés et les maquis ligno-herbacés. Les feux répétés seraient la cause principale du franchissement de ce seuil. L’augmentation de la biomasse végétale constituerait en effet le facteur-clé contribuant à accroître la stabilité des agrégats entre ces deux stades. Ainsi, la protection contre les feux, associée à la promotion des successions végétales à travers l’utilisation d’espèces potentiellement facilitatrices comme Costularia arundinacea pourrait constituer une stratégie efficiente pour limiter l’érosion des Ferralsols. De plus, l’influence des communautés végétales (e.g. composition floristique) et fongiques (e.g. biomasse) sur la stabilité des agrégats est clairement mise en exergue. La troisième partie vise à évaluer la capacité d’espèces végétales, associées à des champignons mycorhiziens, à accroître la stabilité des agrégats, mais aussi à identifier les traits racinaires et les associations mycorhiziennes contribuant à cet accroissement. Dans cette partie, nous mettons en évidence que la combinaison de valeurs élevées des traits racinaires « Root Mass Density – Root Length Density – pourcentage de racines fines » est efficace pour augmenter la stabilité des agrégats. Par ailleurs, l’efficacité de cette combinaison de traits racinaires est accrue par les symbioses mycorhiziennes. Ainsi, des trois espèces végétales évaluées, Costularia arundinacea serait l’espèce-outil la plus efficace pour accroître la stabilité des agrégats. Ce travail a ainsi permis de mettre en évidence l’influence des traits racinaires et des symbioses mycorhiziennes sur la stabilité des agrégats des Ferralsols sur substrats ultramafiques, que ce soit à l’échelle des espèces ou des communautés végétales. A notre connaissance, ces résultats sont les premiers acquis sur ce type de sol. Ces résultats permettent de formuler des propositions en vue de la restauration écologique des milieux forestiers de Nouvelle-Calédonie afin de limiter l’érosion des sols sur substrats ultramafiques, mais aussi d’esquisser de nouvelles pistes de recherche
Tropical forest ecosystems cover nearly half of the world's forest area. These ecosystems provide basic services for the well-being of our societies (e.g. regulation of material flows, soil preservation) are particularly affected (loss and degradation of forests) by global changes. New Caledonia, and its ultramafic substrates, is no exception to this trend. Mining and fires are responsible for forest regression, fragmentation, degradation and soil erosion. The archipelago is ranked among the hotspots of global biodiversity and the ecological restoration of these ecosystems is a major challenge. The objective of this thesis is to contribute to the ecological restoration of the forests of New Caledonia in order to limit the erosion of soils on ultramafic substrates and is part of the disciplinary field of the ecology of restoration. The scientific objective is to study the influence of mycorrhizal symbiosis and root traits on the erosion of Ferralsols developed on ultramafic substrates through a multi-scale approach. In the first part, we highlight the floristic and structural characteristics of plant communities on ultramafic substrates. These suggest an increased expression of the root traits of dominant species in monodominant forests. The central place of fire and cyclones in the dynamics of plant succession is also emphasized, as well as mycorrhizal symbioses in maintaining the monodominance of Nothofagus aequilateralis. In the second part, our work suggests the existence of a biotic threshold between degraded ligno-herbaceous maquis and ligno-herbaceous maquis. Repeated fires would be the main cause of crossing this threshold. The increase in plant biomass would be the key factor contributing to the stability of the aggregates between these two stages. Thus, fire protection combined with the promotion of plant successions through the use of potentially facilitating species such as Costularia arundinacea could be an efficient strategy for limiting erosion of Ferralsols. In addition, the influence of plant (e.g. floristic composition) and fungal communities (e.g. biomass) on the stability of aggregates is clearly highlighted. The third part aims to evaluate the ability of plant species, combined with mycorrhizal fungi, to increase the stability of aggregates, but also to identify root traits and mycorrhizal associations contributing to this increase. In this section, we demonstrate that the combination of high values for “Root Mass Density - Root Length Density – percentage of fine roots” is effective in increasing aggregate stability. Moreover, the efficacy of this combination of root traits is enhanced by mycorrhizal symbiosis. Thus, of the three plant species evaluated, Costularia arundinacea would be the most effective tool species for increasing the stability of aggregates. This work allowed us to highlight the influence of root traits and mycorrhizal symbiosis on the stability of soil aggregates on Ferralsols on ultramafic substrates, at the scale of plant communities or at the level of plant species. To our knowledge, these results are the first to be acquired on this type of soil. These results make it possible to formulate proposals for the ecological restoration of forest ecosystems in New Caledonia in order to limit soil erosion on ultramafic substrates, but also to sketch new avenues of research

碩士
國立屏東科技大學
環境工程與科學系所
102
Ultramafic rocks are derived from hot sea water under high pressure for serpentinization, and then transform as serpentinite, which are widely distributed in the intersection of tectonic plates. Heavy metals are enriched in these rocks including chromium and nickel. This study selected 50 soil samples from (A), (B), and (C) in eastern Taiwan to explore the soil basic properties related to bioavailability of Cr and Ni. Results show that the total chromium and nickel were higher than the soil pollution control levels (Cr: 250 mg/kg, Ni: 200 mg/kg) in some soil samples. By using 0.1N HCl and 0.005M DTPA extraction methods, the Ni extracted concentration was higher than Cr. Therefore, the mobility of Ni was higher than that of Cr. In addition, this study found no significant correlation of the metals between soil and crop.

Ultramafics cover extensive areas of New Caledonia and present a variety of unique nutritional and metal toxicity problems for plant growth. The flora of these substrates is highly diverse and occurs as vegetation types ranging from a low sclerophyllous maquis (heath) to rainforest. These substrates have been the focus of intensive nickel mining over the last century and are often devoid of vegetation for several decades. This lack of plant establishment is a major environmental concern in New Caledonia and has been the focus of revegetation research. The genus Gymnostoma has received particular attention because of its nitrogen fixing association with Frankia and dominance in vegetation types which might be interpreted as a reflecting successional progression after fire. An understanding of the mechanisms surrounding these successional patterns might assist in solving practical issues of mine site revegetation with native species. This thesis set out to firstly determine whether vegetation types containing Gymnostoma are successional communities, secondly to examine certain key processes which appear to be driving vegetation patterns, and thirdly, to identify the role of Gymnostoma in ultramafic vegetation. Key processes associated with vegetation were examined experimentally to determine their influence on plant growth on a range of ultramafic substrates. Field surveys exammmg vegetation patterns and processes were carried out on three ultramafic soil types supporting Gymnostoma vegetation: iron crust oxisol, eroded oxisol and hypermagnesian soil. These three soil types have distinct chemical and physical properties which may affect plant growth. Floristic records from each soil type were firstly examined using MDS to determine floristic associations and subsequently with a successional index constructed from a PCA ordination of vegetation structure. The successional indices explained much of the variation on MDS axes which suggested that ultramafic vegetation patterns primarily reflects a post-fire succession. Fire records, annual growth rings of fire sensitive Dacrydium araucarioides and demographic trends in species composition also support a post-fire succession pattern. The succession pattern was found to be composed of an early successional group of maquis species which either (i) decline or (ii) persist, and (iii) a late successional group of forest species. Another important pattern revealed in surveys is that early ultramafic successional stages progress more slowly than tropical vegetation on other soil types. More importantly, certain processes appear to be critical at early successional stages and predetermine later successional development. Surveys of abandoned mine sites set out to determine what processes appear to be influencing plant establishment at early successional stages. The evidence implies that most species are dispersal limited and show an abrupt decline in abundance away from adjacent vegetation. Primary colonist establishment is more abundant on crevice sites which trap seed, and seedlings show higher rates of survival in such areas. The primary colonists eventually generate a micro-environment providing shade and litter which supports all of the subsequent colonisation of bare ground. Shade and litter levels were regarded as important factors driving succession on ultramafics and their effects at both the community and plant level were examined. Measures of light regimes in successional vegetation indicated that light (PAR) declined with the development of vegetation cover over time. These changes in incident solar radiation effect the community composition depending on species light requirements for photosynthesis. Chlorophyll fluorescence measurements of plants in natural vegetation and in field experiments indicated that seedlings on bare ultramafic soil experienced chronic photoinhibitive stress from a combination of high light and substrate conditions. Seedlings under shade cloth and underneath tree canopies potentially received less light for photosynthesis but exhibited less stress indicative of photoinhibition. Therefore, shade may be crucial for seedling survival at early successional stages. Furthermore, plant species responded to high light conditions depending on their successional status. Maquis species generally overcame photoinhibitive effects of bare ground environments once they attained a certain age. In contrast, forest species continued to exhibit photoinhibitive stress on bare ground environments. Measures of soil and litter nutrient content indicate that N, P, Kand Ca content increased with successional progression. Gymnostoma plays a key role in the development of later successional phases by providing a major source of nitrogen through its Frankia association. This nitrogen is released along with other nutrients as an abundant litterfall that gradually increases soil nutrient pools over time through slow decay. Glasshouse experiments indicated that leachates arising from slow cladode decay had no allelopathic effect on plant growth. However, litter build up in late maquis phases physically excluded large seeded species from establishing. A fire susceptibility index was constructed from litter and vegetation properties of successional vegetation. It indicates that Gymnostoma may raise the susceptibility of maquis because its open canopy allows litter beds to remain dry and flammable. However, Gymnostoma deplancheanum and G. chamaecyparis are able to persist on their respective soil types even at high fire frequencies because rocky terrain reduces fire spread and protects patches of vegetation. In contrast, G. intermedium appears to have been excluded from early successional vegetation on eroded oxisol by a continuous cover of woody sedge maquis which is highly flammable. The eventual dominance of broad leafed vegetation at later succession forest stages decreases the fire susceptibility of these communities. Results of field experiments indicate that slow maquis species growth is primarily due to the low nutrient status of ultramafic soils. Plants which received low doses of fertiliser and/ or litter showed a significant positive response in terms of height and relative shoot growth. Fertiliser applications also raised the total Frankia nodule weight per plant, indicating that Frankia responds positively to slight increases in phosphorus. Contrary to expectation, lime applications had no effect on maquis species shoot growth. Lime additions resulted in fewer Frankia nodules and more extensive root systems in Gymnostoma seedlings by reducing the availability of other nutrients. In summary, it is concluded that Gymnostoma dominated maquis represents a post-fire succession. Colonisation at early successional stages is dispersal limited and highly dependent upon the availability of crevices. Once pioneer plants have established, litter and shade levels become crucial factors in facilitating further succession. The relative abundance of Gymnostoma determines the rate and direction of this successional change.

Ultramafic rocks and soils are of interest because (1) they provide unique plant growth environments, (2) environmental hazards such as chrysotile asbestos may be present, and (3) valuable deposits of asbestos, and minerals containing Mg, Cr, Ni, Co and Pt may be present. Information on ultramafic soils is useful for alleviating environmental problems associated with ultramafic terrain, and for exploiting the opportunities associated with ultramafic mineral deposits. This thesis presents new information on the weathering status of ultramafic soils that formed since the most recent advance of continental ice sheets in southwestern British Columbia. The effects of eolian and tephra additions on soil formation were also described, and soil processes in ultramafic- and tephra-derived soils were compared. A total of 27 soil profiles were described and sampled at three areas in southwestern British Columbia. Brunisolic soils with composite profiles of tephra overlying serpentinite covered much of the Shulaps ultramafic complex. These soils developed in a dry environment and showed weak profile development. The Tulameen area was characterized by a moderately dry climate, and Brunisolic soils had developed in serpentinized peridotite and dunite. The soils of the Coquihalla serpentine belt had Podzolic profiles which resulted from intense weathering in a moist environment. The weathering status of the soils was investigated using a variety of chemical and mineralogical techniques. Chlorite and mica weathering was observed in clay fractions for the Podzolic soils at the Coquihalla area, while profiles from the Shulaps area had similar clay mineralogy throughout the profiles, as determined by XRD. Serpentine dissolution was indicated by chemical analysis of upland soil profiles. Weathering and leaching depleted Mg from B horizons relative to parent materials. Nickel and Co were redistributed to the C horizons in all but the driest environments, while Mn was less mobile. Chromium was retained in the B horizons of all profiles. The influence of tephra on ultramafic paleosols was minimal, but the addition of colluvial and eolian ultramafic materials to the tephra-derived soils gave rise to soils with the cation exchange complex dominated by Mg, which is more typical of ultramafic soils. Lack of buried organic layers in ultramafic paleosols was interpreted as evidence that modern-day tephra soils in the Shulaps Range were more productive than the ancient ultramafic soils. Weathering experiments showed that trace metals such as Cr, Mn, Co and Ni were preferentially released from serpentine to dilute citric acid solutions compared to major elements such as Mg, Si, and Fe. The results suggest that these potentially toxic trace metals may be released in significant amounts in the early stages of pedogenesis.

Although soils developed from ultramafic parent materials have significance to agriculture, ecology and health, their bio-geochemistry is poorly understood. The mineralogical and bio-geochemistry of soils formed from the ultramafic parent materials of the Great Dyke, Zimbabwe and Gillespie County, Texas was investigated. The objectives were to determine the mineralogical and bio-geochemical properties of the soils in order to assess the potential impact and challenges to agriculture, and environmental quality. Soil samples were taken from the crest, shoulder, footslope and the toeslope. Chemical analyses were performed by nuclear and spectroscopic techniques. Mineral characterization was conducted by x-ray diffraction (XRD) and spectroscopic techniques. Microbial whole-community structure was determined by the fatty acid methyl esters (FAME) technique. The results indicate wide chemical and mineralogical compositions among the studied sites. The soils contain relatively high concentrations of heavy metals (some sites contain Cr(VI)), but low levels of K and Ca. The highest concentrations of trace metal were associated with chromite, Fe oxides and serpentinite. The concentrations of Mg were higher than those of Ca and varied between Zimbabwe and Texas soils largely due to the parent materials. Unique to these soils is the occurrence of talc, serpentine, chlorite, Fe-rich smectite, amphiboles, pyroxenes, Fe and Cr oxides in relatively large amounts. These soils also lack micas and have neglible amounts of kaolinite and feldspars. Palygorskite and serpentine occurred in specific soil horizons and at specific landscape positions. FAME profiles indicate that the soil microbial community structure is predominantly bacteria and fungi (including arbuscular mycorrhiza fungi) at each landscape position across the transect. Biomarkers for actinomycetes were undetectable. The proportions of Gram-positive bacteria were higher than those of the Gram-negative bacteria. Very low levels of nutrients (Ca and K), higher Mg/Ca molar ratios, and the relatively high concentrations of heavy metals in these soils impact agricultural productivity. High concentrations of heavy metals, the presence of the Cr(VI) as well as its great potential to form in these soils might impact microbial activity and environmental quality. The occurrence of fibrous minerals (e.g serpentine and amphiboles) in these soils will likely impact human health.

碩士
國立屏東科技大學
環境工程與科學系所
96
Soil properties are deeply affected by the parent rocks such as levels of major, trace, and rare elements. Silicate minerals is the major part in parent rocks. The silicon dioxide's content is bigger than 65% to be called the acidic rocks, and the silicon dioxide content is smaller than 45% is called the ultramafic rocks. This study is to analyze the soils derived from ultramafic rocks (serpentinites) and acidic rocks. The aims of this work are to: (1) understand the status of vertical distribution of the major, trace and rare elements in the study soils, and (2) correlate the relationships between major, trace and rare elements in the soils. Results indicated that type of parent rock played an important role in affecting the content of trace elements in the soils. The average concentrations of Si,Al, Ti, Sr, Ba, Pb, Sn, Cu, Rb,Y and Ga in the serpentinitic soils and Ti, Ni, Cr and Sn in the soils from acidic rocks are higher than those on the crust of Earth. However, Mg, Al, Ca, Fe, Mn, Ni, Cr, Cu, V, Y and Ga in the serpentinitic soils are higher than those in the soils from acid parent rocks. The maximum level of Cr and Ni is over 4000 mg/kg and the correlation of Cr and Ni with Mg, Fe, Sr is up to 0.75, indicating the high contents of Ni and Cr corresponded to the three elements.

Ultramafic soils present an adverse chemical and physical edaphic environment for plant growth characterized by high metal toxicity, low fertility, and frequently unstable and dry conditions. The associated vegetation tends to be distinct from surrounding areas in species composition and structure and often supports high levels of endemism, speciation, and ecotypic differentiation. The general goals of this thesis were to characterize the influence of ultramafic bedrock on the overlying vegetation in southern British Columbia through a detailed comparison of adjacent ultramafic and non-ultramafic soils and to expand the knowledge of the floristics and ecology of ultramafic sites in the province. Grasshopper Mountain, part of the Tulameen ultramafic complex of southern British Columbia, was selected as the study site since the configuration of adjacent ultramafic and non-ultramafic substrata minimized potential confounding factors. Univariate and multivariate analyses of the soil data revealed three different soil types, each with distinct soil chemistry. The most important factors in distinguishing between soil types were related to soil fertility and metal toxicity. Clear floristic and ecological differences were documented between ultramafic and adjacent non-ultramafic soils. Ultramafic soils supported 28 percent of the local species richness and hosted more rare taxa than non-ultramafic soils. Many species showed patterns of local restriction to or exclusion from ultramafic soil habitats. Patterns of plant family richness and abundance and plant ecological group abundance were distinctly different on ultramafic versus non-ultramafic substrata. Multivariate analyses at the landscape, plant community, and species scales, revealed a widespread influence of ultramafic soils on the vegetation. The landscape scale analysis revealed that the main variation in the vegetation data was related to variation in the measured soil and environmental factors. In the community level analysis four main plant communities were recognized by cluster analysis: 1) ultramafic non-forest, 2) ultramafic forest, 3) non-ultramafic upper elevation forest, and 4) non-ultramafic lower elevation forest. Each of these communities was characterized by multiple significant differences based on ANOVA results of mean soil and environmental factors. Two main soil chemistry gradients were defined using non-metric multidimensional scaling: a primary "toxicity-fertility" gradient and a secondary "alkalinity" gradient which clearly separated the four plant communities within ordination space. The species level analysis revealed clear patterns of species response to ultramafic soils and related factors.
Science, Faculty of
Botany, Department of
Graduate

The Sukinda ultramafic complex hosts the largest chromite deposit in India. Metal contamination in water, soil and sediment around mines is invariably associated due to exposure of overburden to the atmospheric oxygen and water as they contain high concentration of metals. Weathering of ultramafic rocks is recognized as one of the sources of Cr(VI), which is carcinogenic in nature. This work attempts to study the geochemical characteristics of water, soil and sediment vis-à-vis-occurrence of Cr(VI) in order to decipher the source of metal contamination in the Sukinda ultramafic complex. The water in the region is mildly oxidizing as Eh varies from 12.3 to 245.9 mV. Most of the water in the region is alkaline in nature, though some groundwater is acidic, and classified into Mg-HCO3- facies. This Mg-HCO3- type water is derived by the interaction of water with serpentinite that is the most dominant rock type in the region. The Cr(VI) concentration is in decreasing order: mine water (0.01 to 4.25 mg/L) followed by surface water (0.03 to 0.56 mg/L) and ground water (0.01 to 0.59 mg/L). Concentration of Cr(VI) exceeding its maximum permissible limit (0.05 mg/L) in most of the water. Among the Cr-species, mine water mostly dominated by Cr(VI) where as surface water and ground water dominated by Cr(III). Water having high Cr(VI) concentration has pH between 7 and 8.4. The source of Cr(VI) in various hydrological units is attributed to weathering of chromite as Eh is not enough to oxidize Cr(III) to Cr(VI). The occurrence of Cr(VI) in groundwater is maximum among all the reported value so far in the world in similar geological condition. Geochemical modelling using indicates that most of the water is saturated with Ca-Montmorillonite, kaolinite, talc, quartz, illite, goethite and hematite; chrysotile and sepiolite are under saturated in most of the water. Based on enrichment factor, geoaccumulation index, pollution and contamination index, it is confirmed that both soil and sediment are strongly contaminated by Cr, Co, Ni and Mn. Enzyme activities in soil have been significantly reduced by the metal contamination. Activities of urease has shown maximum response to the metal contamination, and thus it can be used as bioindicator of metal contamination in serpentinite derived soil. Presence of goethite, kaolinite, clinochlore and chromite in nano-scale have been identified by using high resolution transmission electron microscope. The goethite has shown maximum capacity to retain Cr along with other metals. The very high level of Cr in soil and sediment is mostly caused due to presence of chromite, kämmererite and clinochlore along with Cr-bearing goethite and kaolinite. Fractionation of metals in soil and sediment indicated that most of the metals are in residual and reducible fraction whereas Cu is mostly in labile form. As the total concentration of Cr and Ni is very high, even a small portion of them in exchangeable fraction can lead severe bioaccumulation and have potential health impact.