Thesis (M.Sc. Agriculture (Pasture Science)) -- University of Limpopo, 2021 / Savanna rangelands are ecosystems which are characterized by the co-existence of scattered trees and shrubs with a continuous grass layer. However, the grass and tree balance has been highly altered as a result of disturbances caused by bush encroachment. Encroaching woody species have been shown to decrease species richness and abundance of the seed bank and ground‐layer diversity. So far little is known on the effect of bush encroachment and soil depth on the soil seed bank diversity in savanna rangelands. The objectives of this mini-dissertation were to (1) determine the influence of soil depth on soil seed bank diversity in bush encroached savanna rangelands, and (2) determine the relationships between soil seed bank herbaceous vegetation and physicochemical properties in encroached rangeland. In order to address these objectives, a savanna rangeland was demarcated into two encroachment gradients spanning from open to encroached rangeland. Within each encroachment gradient, six plots of 10 m x 10 m were randomly selected, whereby soil sampling and herbaceous vegetation were carried out and determined. In each replicate plot per encroachment level, five soil samples were randomly collected at 0-10 and 10-20 cm depths. The number of seedlings of different species emerging from the soil samples was used as a measure of the number of viable seeds in the soil and the composition of the seed bank using the seedling emergence method. The total seed densities showed significant differences (P<0.05) in the 0-10 cm depth layer in the open rangeland and encroached rangeland. Bush encroachment significantly (P<0.05) decreased the seed density of perennial grasses, specifically in 0-10 cm depth layer. Further, species diversity increased with bush encroachment in the 10-20 cm depth layer. Menhinick’s richness index showed no significant difference in the open and encroached rangeland, while species evenness decreased in the 0-10 cm depth layer and increased at 10-20 cm depth.The study also revealed negative correlations between organic carbon, calcium, clay, silt and forbs while mean weight diameter (MWD), a measure of soil aggregate stability was positively correlated with forbs. The canonical correspondence analysis (CCA) showed that pH, phosphorus, potassium and calcium were positively correlated to Eragrostis curvula and magnesium was negatively correlated to Panicum maximum. In open rangeland, CCA revealed that clay content was negatively correlated with species evenness while xii magnesium was negatively correlated to the Shannon Weiner index. Further, silt content was positively correlated with species richness and evenness. In the encroached rangeland, the CCA showed a negative correlation between magnesium and the Shannon Weiner index. The Sørensen’s index between soil seed banks and aboveground vegetation was low with index values of 0.22 and 0.24 in open and encroached rangeland, respectively. / AgriSeta

<p>Rechargeable lithium ion batteries (LIBs) are widely used in various daily life applications including electronic portable devices, cell phones, military applications, and electric vehicles throughout the world. The demand for building a safer and higher volumetric/gravimetric energy density LIBs has increased exponentially for electronic devices and electric vehicles. With the high energy density and longer cycle life, the LIBs are the most prominent energy storage system for electric vehicles. Researchers are further exploring for new materials with a high specific capacity, the MXene has been a promising new anode material for LIBs. The typical MXene material Ti₃C₂T_z has 447mAh/g theoretical capacity, which is higher than traditional graphite (372 mAh/g for LiC₆) based anode.</p> <p>Though LIBs are used in most of the portable energy storage devices, LIBs are still having thermal runaway safety concern, which is caused by three main reasons: mechanical, electrical, and thermal abuse. The thermal runaway is caused by the initiation of solid electrolyte interface (SEI) degradation above 80 °C on the anode surface, generating exothermic heat, and further increasing battery temperature. The SEI is a thin layer formed on anode due to electrolyte decomposition during first few charging cycles. Its degradation at low temperature generates heat inside the LIBs and triggers the thermal runaway. The thermal runaway follows SEI degradation, electrolyte reactions, polypropylene separator melting, cathode decomposition and finally leads to combustion. The thermal runaway mechanism of graphite, which is the most common and commercialized anode material of LIBs, has been studied for years. However, the thermal safety aspects of the new MXene material has not been investigated yet. </p> <p>In this thesis, we primarily used differential scanning calorimetry (DSC) and specially designed multi module calorimetry (MMC) to measure exothermic and endothermic heat generated at <a>Ti₃C₂T_z </a>anode, associated with multiple chemical reactions as the temperature increases. The <i>in-situ</i> MMC technique is employed to study the interactions and chemical reactions of all the components (separator, electrolyte, cathode and MXene anode) in the coin cell for the first time, while the <i>ex-situ</i> DSC is used to investigate the reactions happened on anode side, including electrolyte, PVDF binder, MXene, SEI and intercalated Li. Along with other <a>complementary </a>instruments and methods, the morphological, structural and compositional studies are carried out using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET) surface area measurement and electrochemical measurement to support the thermal analysis. The electrochemical and thermal runaway mechanism of conventional graphitic anode is studied and used for comparison with MXeneanodes.</p> <p>The Ti₃C₂T_z thermal runaway is triggered by SEI decomposition around 120 °C analogous to conventional graphite. The thermal behavior of Ti₃C₂T_z anode is highly dependent on electrode material, surface area, lithiation states, surface morphology, structure and surface-terminating functional groups on Ti₃C₂T_z, which provides more active lithium sites for exothermic reactions with the electrolyte. Especially the terminal groups (-OH, -F, =O, etc.) from the etching process affect the lithium ion intercalation and thermal runaway mechanism. With annealing treatment, the surface-terminating functional groups are modified and can achieve less exothermic heat release. By normalizing the total heat generation by specific capacities of the anode materials, it is observed that Ti₃C₂T_z (2.68 J/mAh) generates slightly less exothermic heat than graphite (2.72 J/mAh) indicating slightly safer nature of Ti₃C₂T_z anode. The <i>in-situ</i> thermal analysis results on the Ti₃C₂T_z half-cell exhibited less total heat generation per mass (1.56 kJ/g) compared to graphite (1.59 kJ/g) half-cell. </p><br>

No description available.

Vor dem Hintergrund zukünftiger Sensoren, basierend auf dem piezoresistiven Effekt von einwandigen Kohlenstoffnanoröhren (SWCNT), werden in dieser Arbeit umfangreiche Ergebnisse zum mechanischen Verhalten von Grenzflächen zwischen SWCNTs und edlen Metallen am Beispiel von Pd und Au präsentiert. Im Fokus steht dabei die Synergie von rechnerischen und experimentellen Methoden Molekulardynamik (MD), nanoskalige Tests und Analytik , um (1) mit guter Genauigkeit maximale Kräfte von gezogenen SWCNTs, welche in Metall eingebettet sind, vorauszuberechnen und (2) einen wertvollen Beitrag zum Verständnis der zu Grunde liegenden Fehlermechanismen zu liefern. Es wurde ein MDModell eines in eine einkristalline Matrix eingebetteten SWCNTs mit Randbedingen eines Auszugsversuchs entwickelt. Mit diesem Modell können Kraft-Weg-Beziehungen und Energieverläufe für einen quasistatischen verschiebungsgesteuerten Auszugsversuch errechnet werden. Das Modell liefert kritische Kräfte bei Versagen des Systems. Des Weiteren können mit diesem Modell der Einfluss des SWCNT-Typus, der Einbettungslänge, der Temperatur, von intrinsischen Defekten und Oberflächengruppen (SFGs) auf das Grenzflächenverhalten untersucht werden. Zum Vergleich wurden kritische Kräfte experimentell durch in situ Auszugsversuche in einem Rasterelektronenmikroskop bestimmt. Es wurde eine sehr gute Übereinstimmung von rechnerischen und experimentellen Daten festgestellt. Der vorherrschende Fehler im Experiment ist der SWCNT-Bruch, jedoch wurden auch einige SWCNT-Auszüge beobachtet. Mit Hilfe der MD-Simulationen wurde gefunden, dass die SFGs als kleine Anker in der umgebenden metallischen Matrix wirken und somit die maximalen Kräfte signifikant erhöhen. Diese Grenzflächenverstärkung kann Zugspannungen verursachen, die genügend hoch sind, so dass SWCNT-Bruch initiert wird. Im Gegensatz dazu zeigten Simulationen von Auszugstests mit idealen SWCNTs nur kleine Auszugskräfte, welche meistens unabhängig von der Einbettungslänge des SWCNTs sind. Dieses Verhalten wird mit einer inkommensurablen Konfiguration der Kristallstrukturen an der Grenzfläche von SWCNTs und der einbettenden Edelmetalle interpretiert. Zur Qualifizierung der Existenz von carboxylatischen Oberflächengruppen auf dem genutzten SWCNT-Material wurden analytische Untersuchungen mittels Fluoreszenzmarkierung von Oberflächengruppen durchgeführt. In Übereinstimmung mit Literaturstellen zum gesicherten Nachweis von SFGs, bedingt durch technologische Behandlungen, weisen diese Experimente stark auf das Vorhandensein von carboxylatischen Oberflächengruppen auf dem genutzten SWCNT-Material hin. Demnach kann der dominante SWCNT-Bruch Fehler durch die Grenzflächenverstärkung auf Grund von SFGs erklärt werden. / In the light of future sensors, that are based upon the piezoresistive effect of singlewalled carbon nanotubes (SWCNTs), this work presents comprehensive results of studies on the mechanical behavior of interfaces between SWCNTs and noble metals using the examples of Pd and Au. With this contribution, the focus is on a synergy between computational and experimental approaches involving molecular dynamics (MD) simulations, nanoscale testing, and analytics (1) to predict to a good degree of accuracy maximum forces of pulled SWCNTs embedded in a noble metal matrix and (2) to provide valuable input to understand the underlying mechanisms of failure. A MD model of a SWCNT embedded in a single crystalline matrix with pull-out test boundary conditions was developed. With this model, force-displacement relations and energy evolutions for a quasi-static displacement controlled test can be computed. The model provides critical forces for failure of the system. Furthermore, the influence of SWCNT type, embedding length, temperature, intrinsic defects and surface functional groups (SFGs) on the interface behavior can be studied using this model. For comparison, critical forces were experimentally determined by conducting pull-out tests in situ, inside a scanning electron microscope. A very good agreement of computational and experimental values was discovered. The dominant failure mode in the experiment was a SWCNT rupture, although several pull-out failures were also observed. From MD simulations, it was found that SFGs act as small anchors in the metal matrix and significantly enhance the maximum forces. This interface reinforcement can lead to tensile stresses sufficiently high to initiate SWCNT rupture. In contrast, pull-out test simulations of ideal SWCNTs show only small pull-out forces, which are mostly independent on SWCNT embedding length. This behavior is interpreted with an incommensurate configuration of crystal structures at the interface between SWCNTs and embedding noble metals. To qualify the existence of carboxylic SFGs on the used SWCNT material, an analytical investigation by means of fluorescence labeling of surface species was performed. In agreement with literature reports on the secured verification of SFGs due to necessary technological treatments, these experiments strongly indicate the presence of carboxylic SFGs on the used SWCNT material. Thus, the dominant SWCNT rupture failure is explained with an interface reinforcement by SFGs.

En raison de leur importante capacité de réponse aux changements environnementaux, les producteurs primaires sont depuis longtemps utilisés comme indicateurs biologiques de la qualité des milieux aquatiques. La Directive Cadre Européenne sur l’Eau (2000/60/CE) préconise ainsi l’utilisation du phytoplancton, du phytobenthos et des macrophytes afin de mesurer l’état écologique des écosystèmes lacustres. Dans cette étude, ces trois compartiments ont été utilisés pour déterminer l’état écologique de cinq lacs localisés dans la région Aquitaine (Sud-Ouest de la France), lacs ayant la particularité de présenter des niveaux trophiques différents. Les résultats ont montré qu’au niveau intra-lac la composition floristique dépend fortement des variables physiques dans la plupart des systèmes tandis qu’au niveau inter-lac celle-ci dépend du niveau trophique. Le phytoplancton s’est révélé être l’indicateur de qualité le plus performant et le seul utilisable dans les eaux ouvertes, et le plus précis dans les systèmes où les macrophytes submergés étaient absents. Cependant, dans les lacs humiques, les assemblages phytoplanctoniques semblent répondre davantage à la turbidité et aux brassages fréquents de la colonne d’eau qu’aux nutriments. Dans de telles conditions, afin de mieux caractériser la qualité de l’eau, l’utilisation complémentaire du phytobenthos et des macrophytes se révèle plus pertinente. En conclusion, considérant les trois compartiments biologiques, la présente étude permet une approche complémentaire de l’état écologique des systèmes lacustres. Certaines des méthodes appliquées ici représentent un outil potentiel de détermination de la qualité de l’eau selon les exigences de la DCE, mais elles nécessitent d’être affinées pour une meilleure évaluation de l’état écologique des lacs français. Une attention particulière a été portée aux taxa exotiques observés dans ces lacs tempérés, et cet aspect doit être pris en considération lors de l’évaluation écologique. En effet, ces espèces sensiblement avantagées par les conséquences du changement climatique, peuvent altérer la structure et le fonctionnement des écosystèmes aquatiques en place, et aboutir à une perte de diversité. / Due to their important ability to respond to environmental changes, primary producers have been used for a long time as biological indicators of water quality. The Water Framework Directive (2000/60/EC) recommends the use of the phytoplankton, phytobenthos (diatoms) and macrophytes in the ecological status assessment of lakes. In this study, these three compartments have been used to determine the ecological status of five lakes located in the Aquitaine region (southwest of France) with different trophic status. The results showed that within lakes, the floristic composition in most of the systems strongly depends on physical parameters whereas among lakes it depends on the trophic status. The phytoplankton proved to be the most powerful indicator of quality in open-water areas as well as in systems where submerged macrophytes are absent. However, in the humic lakes, the phytoplankton assemblages seem to respond more to turbidity and mixing than to nutrient load. Under such conditions, water quality could be underestimated and the complementary use of phytobenthos and macrophytes appears more appropriated. In conclusion, considering the three biological elements, the present study allows a complementary approach of the ecological status of the lakes. Some of the methods applied here represent a potential tool for the assessment of the ecological status in the context of WFD, but they need to be refined to assess more properly the ecological status of French lakes. A special attention was paid to exotic taxa observed in these temperate lakes, and this aspect must be taken into account in the ecological assessment. Indeed, these species favoured by the consequences of the climate change, can modify the structure and functioning of the aquatic ecosystems, and lead to a loss of diversity.

A Araucaria angustifolia, conhecida como Pinheiro-do-Paraná é uma espécie ameaçada de extinção no Brasil, está inserida num bioma rico em biodiversidade, a Mata Atlântica, e muito pouco se conhece sobre os atributos microbiológicos dessas florestas. Este trabalho teve como objetivo avaliar potenciais atributos microbiológicos do solo e algumas variáveis ambientais (atributos químicos, físicos e efeito sazonal), a fim de estabelecer bioindicadores de qualidade do solo em Florestas de Araucária. Os estudos foram conduzidos em dois parques estaduais localizados em diferentes regiões do Estado de São Paulo, no município de Campos do Jordão (Parque Estadual de Campos do Jordão - PECJ), nos municípios de Apiaí e Iporanga (Parque Estadual Turístico do Alto Ribeira - PETAR) e também no município de Barra do Chapéu. Foram escolhidas três áreas no PETAR: FN floresta nativa de araucária, ND floresta de araucária com distúrbio antropogênico e PL plantio de araucária; e quatro áreas foram selecionadas no PECJ: FN floresta nativa de araucária, ND floresta de araucária com distúrbio antropogênico, PL plantio de araucária e PF plantio de araucária com ocorrência de fogo acidental. Ao acaso, foram selecionadas quinze árvores de araucária por área e sob a copa de cada uma delas foram retiradas amostras na profundidade de 0 a 20 cm, nas épocas seca e de chuva. Foram avaliados os atributos microbiológicos: arilsulfatase (ARIL), fosfatase ácida (FOSF), -glicosidase (GLIC), desidrogenase (DESID), nitrogênio (NBM) e carbono da biomassa microbiana (CBM), Número Mais Provável (NMP) de amonificantes (AMO), nitritadores (NITRI), nitratadores (NITRA) e desnitrificantes (DESN), respiração basal (RESP), respiração induzida por substrato (RIS), quociente metabólico (qCO2) e microbiano (qMIC). Além disso, foram estabelecidos perfis de ácidos graxos ligados a ésteres de fosfolipídios (EL-PLFAs) e o perfil de capacidade de utilização de substratos de carbono (Biolog). Alguns parâmetros químicos foram avaliados (pH, H++Al3+, Al3+, Ca2+, Mg2+, K+, P, S, N, carbono orgânico total e a capacidade de troca catiônica) e físicos (teores de argila, silte e areia). Verificou-se que o PL do PETAR e PF do PECJ foram relacionados aos atributos microbiológicos ARIL, DESN, CBM e qMIC nos dois períodos. A partição da variabilidade revelou que a atividade microbiana foi influenciada mais pelas variáveis físico-quimicas do solo do que pelas áreas e épocas de coleta. Foram identificados perfis de ácidos graxos semelhantes aos aqui obtidos, PETAR e PECJ, em um trabalho anterior no PECJ, o que pode ser indicação de um padrão de EL-PLFA próprio do ecossistema de araucária. Os ácidos graxos 10Me18:0 (actinobactéria), a relação ácido graxo saturado/insaturado (sat/insat), o consumo dos substratos -metil-D-glicosídeo e o ácido 2-hidroxibenzóico foram também relacionados às áreas PL (PETAR) e PF (PECJ) nos períodos avaliados. Já os ácidos graxos 18:19c (fungo) e 16:17c (bactéria Gram-), o consumo dos substratos glicose-1-fosfato, -D-lactose e ácido -hidroxibutírico estavam relacionados às áreas impactadas dos dois parques durante os períodos de seca e chuva. Portanto, esses atributos microbiológicos são potenciais indicadores de qualidade do solo em Florestas de Araucária, no entanto, novas avaliações são necessárias para as devidas validações dos bioindicadores e monitoramento dessas áreas. / Araucaria angustifolia, also called Brazil Pine, is an endangered species in Brazil. It is part of one of the richest ecosystems in biodiversity, the Atlantic Forest, and little is known about the soil microbiological attributes in this forest. The objective was to evaluate the potential of the soil microbiological attributes and some environmental variables (physical-chemical properties and seasonal effect) to act as bioindicators of soil quality in Araucaria Forests. This study was undertaken in two different state parks in the São Paulo State, in Campos do Jordão county (Campos do Jordão State Park - PECJ), and in Apiaí and Iporanga counties (Alto Ribeira Touristic State Park - PETAR) and also in Barra do Chapéu county. Three areas were surveyed in PETAR: FN Native Araucaria forest, ND Native Araucaria forest with anthropogenic disturbance, and PL Reforested Araucaria; and four areas in PECJ: FN Native Araucaria forest, ND Native Araucaria forest with anthropogenic disturbance; PL Reforested Araucaria, and PF Araucaria reforestation submitted to an accidental fire. Fifteen Araucaria trees were selected at random in each area and the soil and roots were sampled at 0 20 cm depth, in two contrasting seasons (dry and wet). The microbiological attributes evaluated were: arylsulfatase (ARIL), acid phosphatase (FOSF), -glucosidase (GLIC), dehydrogenase (DESID), carbon (CBM) and nitrogen microbial biomass (NBM), most probable number (NMP) of bacterial ammonium oxidizers (AMO), nitrite oxidizers (NITRI), nitrate oxidizers (NITRA) and denitrifiers (DESN), basal microbial respiration (RESP), substrate induced respiration (RIS), and metabolic (qCO2) and microbial quotient (qMIC). Additionally we determined the phospholipid fatty acid profiles (ELPLFA) and the community level physiological profile (Biolog). Some chemical attributes were evaluated (pH, H++Al3+, Al3+, Ca2+, Mg2+, K+, P, S, CEC, C/N ratio, total organic carbon (COT), total nitrogen (NT), as well as some physical ones (soil texture: clay, sand and silt contents). There was a high correlation between the PL of PETAR and the PF of PECJ and the microbiological attributes ARIL, DESN, CBM and qMIC in both periods. The partitioning of the variability evidenced that microbial activity was influenced in a higher degree by the physical-chemical properties of soil than by study areas or periods. We identified similar fatty acid profiles in PETAR and PECJ and they were also similar to the ones found in a previous work in PECJ, what could indicate a specific EL-PLFA pattern in the Araucaria ecosystem. The fatty acids 10Me18:0 (actinobacteria), the saturated/unsaturated fatty acid ratio (sat/insat), the substrate utilization of -methyl-D-glucoside and 2-hydroxybenzoic acid were also related to PL (PETAR) and PF (PECJ), in both periods. The 18:19c fatty acid (fungi) and 16:17c (Gram-), the glucose-1-phosphate, -D-lactose and -hydroxybutyric acid were C-source for microbial communities of the impacted areas in both parks during the wet and dry periods. Therefore, these attributes are potential microbial indicators of soil quality in Araucaria forests, however, new evaluations are required to confirm these biomarkers and to monitor these areas.

A Araucaria angustifolia, conhecida como Pinheiro-do-Paraná é uma espécie ameaçada de extinção no Brasil, está inserida num bioma rico em biodiversidade, a Mata Atlântica, e muito pouco se conhece sobre os atributos microbiológicos dessas florestas. Este trabalho teve como objetivo avaliar potenciais atributos microbiológicos do solo e algumas variáveis ambientais (atributos químicos, físicos e efeito sazonal), a fim de estabelecer bioindicadores de qualidade do solo em Florestas de Araucária. Os estudos foram conduzidos em dois parques estaduais localizados em diferentes regiões do Estado de São Paulo, no município de Campos do Jordão (Parque Estadual de Campos do Jordão - PECJ), nos municípios de Apiaí e Iporanga (Parque Estadual Turístico do Alto Ribeira - PETAR) e também no município de Barra do Chapéu. Foram escolhidas três áreas no PETAR: FN floresta nativa de araucária, ND floresta de araucária com distúrbio antropogênico e PL plantio de araucária; e quatro áreas foram selecionadas no PECJ: FN floresta nativa de araucária, ND floresta de araucária com distúrbio antropogênico, PL plantio de araucária e PF plantio de araucária com ocorrência de fogo acidental. Ao acaso, foram selecionadas quinze árvores de araucária por área e sob a copa de cada uma delas foram retiradas amostras na profundidade de 0 a 20 cm, nas épocas seca e de chuva. Foram avaliados os atributos microbiológicos: arilsulfatase (ARIL), fosfatase ácida (FOSF), -glicosidase (GLIC), desidrogenase (DESID), nitrogênio (NBM) e carbono da biomassa microbiana (CBM), Número Mais Provável (NMP) de amonificantes (AMO), nitritadores (NITRI), nitratadores (NITRA) e desnitrificantes (DESN), respiração basal (RESP), respiração induzida por substrato (RIS), quociente metabólico (qCO2) e microbiano (qMIC). Além disso, foram estabelecidos perfis de ácidos graxos ligados a ésteres de fosfolipídios (EL-PLFAs) e o perfil de capacidade de utilização de substratos de carbono (Biolog). Alguns parâmetros químicos foram avaliados (pH, H++Al3+, Al3+, Ca2+, Mg2+, K+, P, S, N, carbono orgânico total e a capacidade de troca catiônica) e físicos (teores de argila, silte e areia). Verificou-se que o PL do PETAR e PF do PECJ foram relacionados aos atributos microbiológicos ARIL, DESN, CBM e qMIC nos dois períodos. A partição da variabilidade revelou que a atividade microbiana foi influenciada mais pelas variáveis físico-quimicas do solo do que pelas áreas e épocas de coleta. Foram identificados perfis de ácidos graxos semelhantes aos aqui obtidos, PETAR e PECJ, em um trabalho anterior no PECJ, o que pode ser indicação de um padrão de EL-PLFA próprio do ecossistema de araucária. Os ácidos graxos 10Me18:0 (actinobactéria), a relação ácido graxo saturado/insaturado (sat/insat), o consumo dos substratos -metil-D-glicosídeo e o ácido 2-hidroxibenzóico foram também relacionados às áreas PL (PETAR) e PF (PECJ) nos períodos avaliados. Já os ácidos graxos 18:19c (fungo) e 16:17c (bactéria Gram-), o consumo dos substratos glicose-1-fosfato, -D-lactose e ácido -hidroxibutírico estavam relacionados às áreas impactadas dos dois parques durante os períodos de seca e chuva. Portanto, esses atributos microbiológicos são potenciais indicadores de qualidade do solo em Florestas de Araucária, no entanto, novas avaliações são necessárias para as devidas validações dos bioindicadores e monitoramento dessas áreas. / Araucaria angustifolia, also called Brazil Pine, is an endangered species in Brazil. It is part of one of the richest ecosystems in biodiversity, the Atlantic Forest, and little is known about the soil microbiological attributes in this forest. The objective was to evaluate the potential of the soil microbiological attributes and some environmental variables (physical-chemical properties and seasonal effect) to act as bioindicators of soil quality in Araucaria Forests. This study was undertaken in two different state parks in the São Paulo State, in Campos do Jordão county (Campos do Jordão State Park - PECJ), and in Apiaí and Iporanga counties (Alto Ribeira Touristic State Park - PETAR) and also in Barra do Chapéu county. Three areas were surveyed in PETAR: FN Native Araucaria forest, ND Native Araucaria forest with anthropogenic disturbance, and PL Reforested Araucaria; and four areas in PECJ: FN Native Araucaria forest, ND Native Araucaria forest with anthropogenic disturbance; PL Reforested Araucaria, and PF Araucaria reforestation submitted to an accidental fire. Fifteen Araucaria trees were selected at random in each area and the soil and roots were sampled at 0 20 cm depth, in two contrasting seasons (dry and wet). The microbiological attributes evaluated were: arylsulfatase (ARIL), acid phosphatase (FOSF), -glucosidase (GLIC), dehydrogenase (DESID), carbon (CBM) and nitrogen microbial biomass (NBM), most probable number (NMP) of bacterial ammonium oxidizers (AMO), nitrite oxidizers (NITRI), nitrate oxidizers (NITRA) and denitrifiers (DESN), basal microbial respiration (RESP), substrate induced respiration (RIS), and metabolic (qCO2) and microbial quotient (qMIC). Additionally we determined the phospholipid fatty acid profiles (ELPLFA) and the community level physiological profile (Biolog). Some chemical attributes were evaluated (pH, H++Al3+, Al3+, Ca2+, Mg2+, K+, P, S, CEC, C/N ratio, total organic carbon (COT), total nitrogen (NT), as well as some physical ones (soil texture: clay, sand and silt contents). There was a high correlation between the PL of PETAR and the PF of PECJ and the microbiological attributes ARIL, DESN, CBM and qMIC in both periods. The partitioning of the variability evidenced that microbial activity was influenced in a higher degree by the physical-chemical properties of soil than by study areas or periods. We identified similar fatty acid profiles in PETAR and PECJ and they were also similar to the ones found in a previous work in PECJ, what could indicate a specific EL-PLFA pattern in the Araucaria ecosystem. The fatty acids 10Me18:0 (actinobacteria), the saturated/unsaturated fatty acid ratio (sat/insat), the substrate utilization of -methyl-D-glucoside and 2-hydroxybenzoic acid were also related to PL (PETAR) and PF (PECJ), in both periods. The 18:19c fatty acid (fungi) and 16:17c (Gram-), the glucose-1-phosphate, -D-lactose and -hydroxybutyric acid were C-source for microbial communities of the impacted areas in both parks during the wet and dry periods. Therefore, these attributes are potential microbial indicators of soil quality in Araucaria forests, however, new evaluations are required to confirm these biomarkers and to monitor these areas.

Ecosystems currently face widespread biodiversity losses and other environmental disturbances, such as climate warming, related to increased anthropogenic activities. Within this context, scientists consider the effects of such changes on the biodiversity, and hence on the activity, of soil microorganisms. Indeed, soil microorganisms mediate a wide range of soil processes. Currently, knowledge on soil microbial diversity is still limited, partially due to technical limitations. The advent of molecular-based analyses now allows studying the soil microbial diversity. These advances in the study of soil microbial communities have lead to a growing evidence of the critical role played by the microbial community in ecosystem functioning. This relationship is supposed to be relevant for narrow processes, regulated by a restricted group of microorganisms, such as the nitrification process. This PhD thesis aimed at studying ammonia oxidizing bacteria (AOB) community structure and richness as an integrated part of soil functioning. This research aimed at investigating the effect of aboveground plant diversity on ammonia oxidizing bacteria diversity and function in forest and grassland soils with focus on the influence of (a) functional group identity of grassland plants (legumes, grasses, forbs), (b) grassland plant species richness and (c) tree species, on AOB diversity and function. Another objective of this research was to study the effect of a 3°C increase in air temperature on AOB diversity and function. The link between AOB diversity and function (potential nitrification) is also investigated. For grassland ecosystems, a microcosm experiment was realized. An experimental platform containing 288 assembled grassland communities was established in Wilrijk (Belgium). Grassland species were grown in 12 sunlit, climate controlled chambers. Each chamber contained 24 communities of variable species richness (S) (9 S=1, 9 S=3 and 6 S=9).The grassland species belonged to three functional groups: three species of each grasses (Dactylis glomerata L., Festuca arundinacea SCHREB., Lolium perenne L.), forbs (non-N-fixing dicots; Bellis perennis L., Rumex acetosa L., Plantagolanceolata L.), and legumes (N-fixing dicots; Trifolium repens L., Medicago sativa L., Lotus corniculatus L.). Half of these chambers were exposed to ambient temperature and the other half were exposed to (ambient +3°C) temperature. One ambient and one (ambient+3°C) chambers were destructively harvested 4, 16 and 28 months after the start of the experiment. The influence of plant functional group identity on the nitrification process and on AOB community structure and richness (AOB diversity) was assessed in soils collected from the first two destructive amplings (chapter 2). The effect of plant species richness on AOB diversity and function was considered for soils sampled after 16 and 28 months (chapter 3). AOB function was determined by potential nitrification. AOB community structure and richness were assessed by polymerase chain reaction followed by denaturing gradient gel electrophoresis (DGGE) and sequencing of excised DGGE bands. I found that functional group identity can affect AOB community structure. In particular, the presence of legumes, both in monoculture or in mixture with forbs and grasses, lead to AOB community composition changes towards AOB clusters tolerating higher ammonium concentrations. This change in AOB community structure was only linked to increased potential nitrification under monocultures of legumes, when ammonium was supposed to be not limiting. This study revealed that physiological attributes of AOB and resource availability may be important factors in controlling the nitrification process. This research showed that the impact of plant species richness on the nitrification process could be mediated by the interactions between plants and AOB, through competition for substrate. A 3°C increase in air temperature did not affect AOB community structure, richness or function. In forest ecosystems, we studied the effect of tree species in forest sites located in Belgian and in the Grand-Duchy of Luxembourg covered each by several deciduous or coniferous tree species (Fagus sylvatica L., Quercus petraea (Mattuschka) Lieblein, Picea abies (L.) Karst, Pseudotsuga menziesii (Mirbel) Franco). We investigated the influence of these tree species on microbial processes (chapter 5) related to C and N cycling, particularly with emphasize on the nitrification process and on the diversity of AOB (chapter 6). The results showed that the effect of tree species on net N mineralization was likely to be mediated through their effect on soil microbial biomass, reflecting their influence on organic matter content and carbon availability. Influence of tree species on nitrification (potential and relative) might be related to the presence of ground vegetation through its influence on soil ammonium and labile C availability. AOB community structure was more site-specific than tree specific. However, within sites, AOB community structure under broadleaved trees differed from the one under coniferous trees. The effect on tree species on AOB was likely to be driven by the influence of tree species on net N mineralization, which regulates the substrate availability for AOB. The results also demonstrated that the relationship between AOB diversity and function might be related both to AOB abundance and AOB community structure and richness. This thesis showed no clear relationship between AOB community structure or richness and AOB function. However, we revealed that aboveground grassland plant richness, grassland plant functional groups and tree species influence AOB community structure and richness. Actuellement, les écosystèmes sont soumis à dimportantes pressions anthropiques et environnementales, pouvant aboutir à des pertes massives de biodiversité. Les scientifiques sinterrogent sur limpact de ces perturbations sur la diversité et, par conséquent, sur lactivité des microorganismes du sol. En effet, ceux-ci régulent de nombreux processus du sol. Actuellement, de nombreuses lacunes subsistent dans la connaissance de la diversité microbienne du sol. Celles-ci peuvent être partiellement attribuées aux difficultés méthodologiques associées à l'étude des micro-organismes du sol. Lavènement des techniques moléculaires nous permet de combler ces lacunes. Les avancées réalisées dans l'étude des communautés microbiennes du sol ont mis en évidence le rôle crucial joué par les communautés microbiennes dans le fonctionnement des écosystèmes. De plus, il semblerait que les processus régulés par un groupe restreint dorganismes, tel le processus de nitrification, soient plus sensibles à toute altération de la communauté. Lobjectif de cette thèse était détudier la structure de la communauté ainsi que la richesse (nombre de bandes DGGE) des bactéries oxydant lammoniac (AOB) comme une partie intégrante du fonctionnement des sols. Notre étude se focalisait sur linfluence de (a) différents groupes fonctionnels de plantes (graminées, légumineuses, dicotylédones), (b) communautés de plantes présentant une richesse spécifique croissante et (c) différentes essences forestières, sur la diversité (structure de la communauté et richesse des AOB) et la fonction des AOB. Cette recherche étudiait également limpact dune augmentation de température de 3°C sur ces paramètres. Létablissement dun lien éventuel entre la diversité et la fonction (nitrification potentielle) des AOB a aussi été envisagé. Concernant les écosystèmes prairiaux, nous avons réalisé une étude en microcosmes. Une plateforme expérimentale comprenant 288 communautés artificielles de plantes a été établie à Wilrijk (Belgique). Cette plateforme consistait en 12 chambres, dont une moitié était à température ambiante et la seconde était à température ambiante augmentée de 3°C. Chaque chambre contient 24 communautés de plantes de richesse spécifique variable (9 S=1, 9 S=3 et 6 S=9). Les communautés de plantes sont créées avec 9 espèces de plantes appartenant à trois groupes fonctionnels : 3 espèces de graminées (Dactylis glomerata L., Festuca arundinacea SCHREB., Lolium perenne L.), de légumineuses (dicotylédones fixatrices dazote ;Trifolim repens L., Medicago sativa L., Lotus corniculatus L.), et de dicotylédones non fixatrices dazote (Bellis perennis L., Rumex acetosa L., Plantago lanceolata L.). Les sols issus dune chambre à température ambiante et dune chambre à température ambiante augmentée de 3°C ont été échantillonnés, respectivement, 4, 16 et 28 mois après le début de lexpérimentation. Linfluence des groupes fonctionnels de plantes sur le processus de nitrification ainsi que sur la structure de la communauté et la richesse des AOB a été mesuré sur les sols issus des deux premiers échantillonnages (chapitre 2). Nous avons mesuré leffet de la richesse croissante en plantes sur la diversité et lactivité des AOB sur les sols échantillonnés après 16 et 28 mois dexpérimentation (chapitre 3). La structure de la communauté ainsi que la richesse des AOB ont été évaluées à laide dune amplification spécifique par réaction de polymérisation en chaîne (PCR) de lADN génomique extrait du sol suivie par une séparation par électrophorèse sur gel dacrylamide en présence dun gradient dénaturant (DGGE). Nous avons identifié les différentes AOB présentes par séquençage des bandes DGGE excisées. Nos résultats ont montré que les différents groupes fonctionnels peuvent affecter la structure de la communauté des AOB. En particulier, la présence de légumineuses, aussi bien en monoculture quen mélange avec des graminées ou des dicotylédones non fixatrices dazote, provoque des changements au sein de la structure de la communauté des AOB, favorisant la présence de clusters tolérants des concentrations en ammonium plus élevées. Ces changements de la structure de la communauté des AOB sont liés à des augmentations de la production potentielle de nitrates (nitrification potentielle) quand lammonium est supposé être non limitant. Cette étude révèle que la physiologie des AOB ainsi que la disponibilité en substrat peuvent être des facteurs majeurs intervenant dans le contrôle du processus de nitrification. Cette recherche montre que linfluence de la richesse spécifique des plantes sur la nitrification pourrait dépendre des interactions entre les plantes et les AOB via la compétition pour le substrat. Une augmentation de la température de lair de 3°C na pas influencé les richesse, structure de la communauté ou les fonctions des AOB. Pour les écosystèmes forestiers, nous aborderons leffet de différentes essences forestières (Picea abies (L.) KARST, Fagus sylvatica L., Quercus petraea LIEBLEIN ; Pseudotsuga menziezii (MIRB.) FRANCO) dans différents peuplements au Grand Duché du Luxembourg et en Belgique. Nous avons étudié l'influence de ces essences forestières sur les processus microbiens (chapitre 5) liés aux cycles du carbone et de lazote, en particulier leur effet sur le processus de nitrification et la diversité des AOB (chapitre 6). Notre étude révèle que linfluence des essences forestières sur la minéralisation nette de lazote pourrait être attribuable à leur effet sur la biomasse microbienne, reflétant ainsi leur effet sur la teneur en matière organique et la disponibilité en carbone. Limpact des essences forestières sur la nitrification (à la fois sur la nitrification relative et sur la nitrification potentielle) serait conditionné par la présence de végétation au sol, en raison de linfluence de celle-ci sur la disponibilité en ammonium et en carbone labile. Nous avons observé que la structure de la communauté des AOB était plus spécifique aux sites quaux essences forestières. Cependant, au sein dun site, elle différait sous feuillus et sous conifères. Les essences forestières influenceraient la structure de la communauté des AOB au travers de limpact quelles ont sur la minéralisation nette de lazote qui régule, quant à elle, la disponibilité en ammonium. Cette recherche démontre que le lien observé entre la diversité et la fonction dépendrait la fois de labondance, de la structure de la communauté et de la richesse des AOB. Cette thèse na révélé aucune relation claire entre la structure de la communauté ou la richesse des AOB et leur fonction. Par contre, nous avons observé que la richesse spécifique et les groupes fonctionnels de plantes prairiales et les essences forestières affectent la structure de la communauté et la richesse des AOB.

Optically transparent carbon based nanomaterials including graphene and carbon nanotubes(CNTs) are promising candidates as transparent conductive electrodes due to their high electrical conductivity coupled with high optical transparency, can be flexed several times with minimal deterioration in their electronic properties, and do not require costly high vacuum processing conditions. CNTs are easily solution processed through the use of surfactants sodium dodecyl sulfate(SDS) and sodium cholate(SC). Allowing CNTs to be deposited onto transparent substrates through vacuum filtration, ultrasonic spray coating, dip coating, spin coating, and inkjet printing. However, surfactants are electrically insulating, limit chemical doping, and increase optical absorption thereby decreasing overall performance of electrodes. Surfactants can be removed through nitric acid treatment and annealing in an inert environment (e.g. argon). In this thesis, the impact of surfactant removal on electrode performance was investigated. Nitric acid treatment has been shown to p-dope CNTs and remove the surfactant SDS. However, nitric acid p-doping is naturally dedoped with exposure to air, does not completely remove the surfactant SC, and has been shown to damage CNTs by creating defect sites. Annealing at temperatures up to 1000°C is advantageous in that it removes insulating surfactants. However, annealing may also remove surface functional groups that dope CNTs. Therefore, there are competing effects when annealing CNT electrodes. The impacts on electrode performance were investigated through the use of conductive-tip atomic force microscopy, sheet resistance, and transmittance measurements. In this thesis, the potential of graphene CNT composite electrodes as high performing transparent electrodes was investigated. As-made and annealed graphene oxide CNT composites electrodes were studied. Finally, a chemical vapor deposition grown graphene CNT composite electrode was also studied.

Le plancton constitue l’essentiel de la biomasse pélagique et est un acteur majeur des cycles biogéochimiques globaux qui régulent le système Terre. Il comprend l'ensemble des organismes portés par les courants, des bactéries aux méduses géantes. La communauté n'est que très rarement étudiée dans son ensemble mais plutôt par fraction. L’expédition Tara Oceans constitue le premier effort de collecte simultané de toutes les classes de taille de plancton à l’échelle de l’océan global. Pour démontrer la faisabilité de cette approche à grande échelle, des échantillons hebdomadaires de plancton, depuis les bactéries jusqu’au macroplancton gélatineux, ont d’abord été analysés en combinant plusieurs instruments d’imagerie sur une période de 10 mois, en un site de référence (point B) dans la rade de Villefranche sur mer. L’imagerie nous a permis de comparer 1) l’information fonctionnelle définie comme l’agrégation de taxons en 18 Groupes Ecologiques de Plancton (GEP), et 2) la structure en taille des communautés échantillonnées sur un intervalle de taille de 6 ordres de grandeur (0.1 µm à 10000 µm). La communauté planctonique au point B évolue en une succession écologique complexe impliquant tous les groupes planctoniques, depuis les bactéries jusqu’aux prédateurs gélatineux du macroplancton. Des évènements impulsifs, tels que des coups de vent, déclenchent des réorganisations de la communauté par un jeu d’interactions entre des contrôles « bottom-up » et « top-down ». Toutefois, le biovolume planctonique total ne varie que d’un seul ordre de grandeur au cours de la période échantillonnée. De même, la structure en taille des communautés planctoniques totales ne varie pas significativement au cours du temps. La stabilité du biovolume total et de la structure en taille suggère que des mécanismes structurant et de compensation forts maintiennent les communautés planctoniques dans un intervalle de biomasse restreint. Le couplage entre données de taille et de taxonomie révèle une réorganisation du réseau trophique entre l’été et l’hiver. En hiver, Le réseau trophique microplancton-zooplancton est dominé par la fonction de broutage. En été, le réseau trophique microplancton-zooplancton est dominé par la fonction de prédation (chaetognathes et gélatineux carnivores). En été, ce réseau trophique s’organise en deux chaines trophiques parallèles et distinctes discriminées par des relations de taille entre proies et prédateurs. Cette réorganisation souligne le rôle clef du zooplancton et de la prédation dans la structuration des communautés planctoniques. Parallèlement à cette analyse temporelle en un point fixe, nous avons montré l’existence de types caractéristiques de communautés zooplanctoniques, associés à des conditions environnementales distinctes, à partir des échantillons de l’expédition Tara Oceans, à l’échelle globale. En utilisant la même méthodologie que pour l’analyse de la dynamique temporelle, nous avons identifié trois types de communautés mésozooplanctoniques à l’échelle globale selon le type d’environement: 1) des communautés associées aux environnements productifs (upwellings côtiers et équatoriaux), 2) des communautés associées aux zones de minimum d’oxygène (OMZs, « Oxygen Minimum Zones »), et 3) des communautés associées aux gyres océaniques oligotrophes. Ce travail constitue une première typologie des communautés zooplanctoniques, structurées en taille et GEP, à l’échelle globale. Il sera complété dans le futur par l’intégration de données issus des autres compartiments planctoniques, et de données d’export vertical de matière organique particulaire pour affiner les estimations des relations qui existent entre phytoplancton, zooplancton et flux biogéochimiques. / Plankton constitutes the bulk of pelagic biomass and plays a major role in the global biogeochemical cycles that regulate the earth system. It encompasses all the organisms that drift with the water masses movements, from bacteria to giant medusae. Studies of the entire community are scarce, and plankton has been traditionally studied by fractions. The Tara Oceans expedition is the first attempt to simultaneously collect plankton in every size classes at the global scale. To demonstrate the feasibility of this approach, samples of plankton from bacteria to gelatinous macroplankton were collected weekly over ten months at a reference site (point B), in Villefranche Bay, northwestern Mediterranean, and analyzed using imaging techniques. Imaging enabled us to compare 1) the functional taxonomic information as derived from the analysis of 18 Plankton Ecological Groups (PEGs), and 2) the size structure of the same planktonic community over 6 orders of magnitude in size. The plankton dynamics at point B are driven by a complex succession process involving all plankton groups, from bacteria to macroplanktonic gelatinous predators. Environmental impulsive events such as wind events trigger sharp community level reorganizations via interplay of bottom-up controls followed by top-down controls. However, the total biovolume of the planktonic community varies within only one order of magnitude over the period studied. In addition, the size structure of the entire community does not vary significantly over time. The total biovolume and size structure stability suggest that strong and compensative mechanisms drive community dynamics within a narrow range of biomass variation. The use of both taxonomic and size structured data reveals a reorganization of the food web between winter and summer. In winter and spring the microplanktoniczooplanktonic food web is shaped by the grazing function. In summer, it is shaped by the predation function (chaetognaths and gelatinous predators). In summer, the food web self organizes in two distinct food chains discriminated by size relations between predators and preys. This reorganization underlines the key role of zooplankton and predation in structuring planktonic communities. In parallel to this temporal dynamics study, we used the Tara Oceans expedition samples to study the global scale distribution of mesozooplankton. We showed that characteristic mesozooplanktonic communities were associated with distinct environmental conditions, at the global scale. Using a similar methodology as for the temporal study we found that three different mesozooplanktonic communities were associated with 1) productive environments (e.g. upwellings), 2) Oxygen Minimum Zones, and 3) Oligotrophic oceanic gyres. This work is the first typology of mesozooplanktonic communities at the global scale. It will be further developed in the future by the integration of other planktonic compartments and particulate organic matter fluxes data, to improve our knowledge on the relations between phytoplankton, zooplankton and particulate organic matter fluxes.