Soil biodiversity is an often overlooked component of global biodiversity, despite being important for supporting soil ecosystem services, notably decomposition processes. As the UK becomes increasingly urbanised, knowledge is required to help gardeners maximise urban green space resources for biodiversity. It is often assumed that non native vegetation has negative impacts on biodiversity, however, this hypothesis has not been tested for soil biodiversity. The overarching aims were to establish whether the geographical origin of vegetation affected soil faunal assemblages and decomposition rates for a UK soil. Traditional taxonomic methods and a molecular phylogenetic approach were used to characterise the Collembola communities of plots planted with vegetation from three geographical regions: ‘Native’, ‘Near native’ and ‘Exotic’. For comparison, additional soil cores were collected from the amenity grassland sites adjacent to the experimental plots, a lowland heath and a semi-natural woodland. No difference was found either in terms of the taxonomic diversity (1-D & H’) or phylogenetic diversity (PD & MPD) for the Collembola, under the different vegetation treatments, although differences in abundance were observed for some taxa (Acari & Collembola). Decomposition rates were assessed for each plot, using both twig (B. pendula) and leaf (Q. robur) litter bags for the soil mesofauna and bait lamina strips for earthworm activity; none of these parameters showed evidence of a vegetation origin effect on decomposition processes. The greatest differences were found when all sites were considered, with distinct Collembola communities found at each of the habitats; the semi-natural habitats had greater Collembola species diversity than the experimental plots, however, the decomposition rates of the latter were significantly higher. The implications of all results have been discussed with regards to the management of gardens for soil biodiversity, reaching the conclusion that vegetation origin is not of paramount importance.

Thesis (M. Appl. Sc.) -- Lincoln University, 2008. / Also available via the World Wide Web.

The objective of this research was to determine the effects of conventional inputs on soil chemical and biological properties compared to organic systems in a four year vegetable rotation. Tillage and cover crops were the same in all treatments to avoid confounding factors often present in similar research. Additional experiments investigated plant gene expression in organic and conventional management systems and in soils with decreased microbial diversity. Experimental plots were prepared in the spring of 2004; four replications of three management treatments, organic, low-input and conventional, were arranged in a randomized complete block design. The rotation consisted of edamame soybean, sweet corn, fallow (pastured poultry in organic plots), and potatoes. Soil samples were taken in the spring and fall of each year, along with data for pest damage, weed control, yield and quality. Soil samples were analyzed for enzyme activity (maximum activity under substrate saturation) and basic soil chemical properties. Treatments were compared over time using 2-Way ANOVA. Multiplex terminal-restriction fragment length polymorphism (M-TRFLP) profiles of the soil microbial community were compared using Multiple Response Permutation Procedures (MRPP). Multi-way ANOVA detected significant treatment effects over time in total carbon, nitrogen, Mehlich III K, Exchangeable K and exchangeable Na (p=0.05). Many significant changes in soil properties over time could not be attributed to treatment effects. All treatments produced similar yields, indicating that successful organic production of these vegetables is possible in Kentucky. Input costs for organic were 37% higher than conventional, due to the cost of organic fertilizer. The organic system required nearly 50% more labor hours than conventional or low-input. The low-input system was the most cost effective, with 58% less input expenses than the conventional system. Microarray analysis of approximately 37,500 Glycine max transcripts did not show significant differences in the gene expression between plants grown organically and conventionally, in plots with significant soil chemical and microbial differences. An experiment in progress is investigating changes in plant gene expression using real time RT-PCR in tomatoes grown in autoclaved soil and native field soil.

Made available in DSpace on 2014-12-17T15:49:13Z (GMT). No. of bitstreams: 1 RuyAAL_DISSERT.pdf: 2128055 bytes, checksum: 8d6cb4ba8070b2733dd933f1021d095c (MD5) Previous issue date: 2013-03-19 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / Arbuscular mycorrhizal fungi (AMF) are obligatory symbiotic organisms that associate with roots of a large number of plant taxa, and are found in all terrestrial ecosystems. These fungi promote greater tolerance to environmental stresses to associated plant, favoring the establishment of plant communities, especially where soil fertility is a limiting factor, as in the Caatinga, an exclusively Brazilian domain that has been focus of research due to its great biodiversity that can help clarify the history of vegetation in South America. Because of the ecological importance of AMF, the limited number of jobs and the potential diversity of the Caatinga, this work aims to inventory the diversity and determine AMF communities in areas with different faces occurrent in FLONA Araripe, Cear? (CE). The sample collection occurred in four periods at the beginning and end of the dry season (August and December 2011, respectively) and rainy (February and June 2012, respectively) in an area of marsh and woodland altitude of the Araripe, Crato, CE. The glomerosporos were extracted by wet sieving and centrifugation in water and sucrose (50%) mounted between slide and coverslip using PVLG and PVLG + Reagent Melzer. In total, we found 46 species of AMF distributed in eight families and 16 genera: Acaulospora (6), Ambispora (1), Cetraspora (2), Dentiscutata (5), Fuscutata (2), Gigaspora (6), Glomus (13) Intraornatospora (1), Kuklospora (1), Orbispora (1), Paradentiscutata (1), Quatunica (1), Racocetra (1), Scutellospora (2), Septoglomus (2) and a new genus. analysis showed that ecological each area of study has its own seasonal dynamics, with an area of woodland with a greater diversity of species throughout the year, while the marsh elevation showed greater variation in species found among the collection periods, showing that vegetation and rainfall has strong influence on the seasonal dynamics of AMF, as well as the availability of nutrients and soil pH so / Os fungos micorr?zicos arbusculares (FMA) s?o organismos simbiontes obrigat?rios de ra?zes de vasto n?mero de t?xons vegetais, sendo encontrados em todos os ecossistemas terrestres. Estes fungos promovem maior toler?ncia a estresses ambientais aos vegetais associados favorecendo o estabelecimento de comunidades vegetais, especialmente quando a fertilidade do solo ? fator limitante, como em ?reas de Caatinga, dom?nio exclusivamente brasileiro que vem sendo foco de pesquisas em fun??o da particular biodiversidade que pode proporcionar maior compreen??o da hist?ria vegetacional de parte da Am?rica do Sul. Devido ? import?ncia ecol?gica dos FMA, ao limitado n?mero de trabalhos e o potencial em diversidade da Caatinga, este trabalho visa inventariar a diversidade e determinar as comunidades de FMA em ?reas com diferentes fisionomias ocorrentes na FLONA Araripe, Cear? (CE). A coleta das amostras ocorreu em quatro per?odos, no in?cio e final da esta??o seca (agosto e dezembro de 2011, respectivamente) e chuvosa (fevereiro e junho de 2012, respectivamente) em uma ?rea de brejo de altitude e de cerrad?o da Chapada do Araripe, Crato, CE. Os glomerosporos foram extra?dos por peneiramento ?mido e centrifuga??o em ?gua e sacarose (50%), montados entre l?mina e laminula utilizando PVLG e PVLG + Reagente de Melzer. No total, foram encontradas 46 esp?cies de FMA distribuidas em oito fam?lias e 16 g?neros: Acaulospora (6), Ambispora (1), Cetraspora (2), Dentiscutata (5), Fuscutata (2), Gigaspora (6), Glomus (13), Intraornatospora (1), Kuklospora (1), Orbispora (1), Paradentiscutata (1), Quatunica (1), Racocetra (1), Scutellospora (2), Septoglomus (2) e um novo g?nero. An?lises ecol?gicas mostraram que cada ?rea de estudo apresenta din?micas sazonais pr?prias, com a ?rea de cerrad?o com maior diversidade de esp?cies ao longo do ano, enquanto que o brejo de altitude mostrou maior varia??o nas esp?cies encontradas entre os periodos de coleta, mostrando que a vegeta??o e a pluviosidade tem forte influ?ncia na din?mica sazonal dos FMA, assim como a disponibilidade de nutrientes e o pH so solo

nÃo hà / Os Fungos MicorrÃzicos Arbusculares - FMA sÃo microrganismos chave tanto em agroecossistemas como em ecossistemas naturais. SÃo responsÃveis por uma simbiose que ocorre com a maioria das plantas vasculares. Atuam em mutualismo com as plantas, auxiliando-as na absorÃÃo de nutrientes pouco mÃveis no solo, alÃm de aumentar a absorÃÃo de Ãgua e protegÃ-las contra patÃgenos, sendo fortemente influenciados por prÃticas agrÃcolas e variaÃÃes ambientais. Neste trabalho avaliaram-se as influÃncias de parÃmetros quÃmicos do solo, perÃodos do ano e quatro diferentes agroecossistemas com fruteiras tropicais (cajueiros - Anacardium occidentale (2 pomares), coqueiros - Cocos nucifera, e gravioleiras - Annona muricata), na diversidade de FMA em comparaÃÃo com uma Ãrea de mata nativa adjacente aos plantios, partindo da hipÃtese de que estes fatores alteram a composiÃÃo da comunidade desses fungos. Foram coletadas amostras de solo na profundidade de 0-20 cm, no perÃodo chuvoso (abril/2009) e seco (outubro/2009), e utilizados Ãndices ecolÃgicos como forma de avaliar as alteraÃÃes entre os sistemas e os perÃodos. No total foram identificados 35 diferentes morfotipos de esporos de FMA. Entre os parÃmetros quÃmicos do solo, o pH mostrou-se negativamente correlacionado com a densidade mÃdia de esporos, o Mg com a riqueza de espÃcies e o Zn com ambos. A densidade mÃdia de esporos foi influenciada negativamente pelos agroecossistemas, pois os maiores valores foram encontrados na Ãrea de mata em ambos os perÃodos, e exceto pela cultura do coqueiro, todas as outras tiveram aumento significativo no perÃodo seco. A riqueza de espÃcies de FMA mostrou-se estÃvel, sendo que apenas a gravioleira apresentou diferenÃa em relaÃÃo aos outros sistemas no perÃodo chuvoso. Jà no perÃodo seco nÃo houve diferenÃa na riqueza entre os sistemas, sendo detectado um aumento na riqueza de espÃcies, comparado ao perÃodo chuvoso. A abundÃncia relativa indicou uma maior dominÃncia nas comunidades no perÃodo chuvoso, e a freqÃÃncia relativa demonstra a prevalÃncia de espÃcies do gÃnero Glomus em todos os sistemas. A maior diversidade de FMA foi constatada no solo cultivado com coqueiro. Houve um aumento generalizado da diversidade no perÃodo chuvoso comparada com o perÃodo seco. A dominÃncia avaliada pelo Ãndice de Simpsom corrobora os resultados obtidos pela abundÃncia relativa, demonstrando que no perÃodo chuvoso a concentraÃÃo de dominÃncia foi maior em todos os sistemas A anÃlise de similaridade, utilizando o Ãndice de Bray-Curtis, demonstra que o perÃodo seco tornou os sistemas mais similares, uma vez que apresentaram maiores valores nesse perÃodo. A anÃlise de agrupamento baseada no Ãndice de similaridade demonstra que, apesar das variaÃÃes de riqueza de abundÃncia, os sistemas foram agrupados igualmente em ambos os perÃodos. A gravioleira formou um grupo isolado, enquanto a Ãrea de mata mostrou-se mais similar a cultura do cajueiro velho. O outro agrupamento foi formado pelo coqueiral e a plantaÃÃo de cajueiro novo. Os resultados deste estudo permitem concluir: as atividades agrÃcolas alteraram a composiÃÃo da comunidade de FMA em relaÃÃo à mata nativa; o agroecossistema cultivado com coqueiro apresentou a maior biodiversidade de FMA dentre os sistemas avaliados; as espÃcies do gÃnero Glomus foram mais abundantes tanto nos agroecossistemas como no ecossistema natural; houve diferenÃa na composiÃÃo e na diversidade da comunidade de fungos entre o perÃodo chuvoso e seco; e a diversidade de esporos de FMA no solo, nÃo se relacionou com a capacidade infectiva nas fruteiras / Arbuscular Mycorrhizal Fungi - AMF are key organisms in natural ecosystems and agroecosystems, as being responsible for a symbiosis that occurs in more than 80% of terrestrial vascular plants. Work in mutualism with plants, helping them with less mobile nutrient uptake, increase the absorption of water, protect them against diseases and are strongly influenced by agricultural practices and environmental changes. This study evaluated the influence of chemical parameters of soil, climate variation in two seasons and four different agroecosystems of tropical fruit trees (cashew- Anacardium occidentale, coconut - Cocos nucifera and soursop - Annona muricata), with the diversity of AMF compared with an area of native forest adjacent to plantations, considering the hypothesis that these factors change the community composition of these fungi. Samples were collected at depth of 0-20 cm in the rainy (April/2009) and dry season (October/2009) and used ecological indexes as a way of evaluating changes in the systems and periods. In total were identified 35 different morphotypes of spores and chemical parameters of the soil indicated that pH was negatively correlated with the average density of spores, Mg with the species richness and Zn with both. The average density of spores was negatively influenced by agroecosystems, because the highest values were found in the forested area in both periods, and except for the coconut (Cocos nucifera L.) crop, all the others had a significant increase in between the periods. Species richness was found to be stable, with only the soursop culture (Annona Muricata) different compared to other systems in the rainy season. During the dry season no differences being detected in richness. The relative abundance indicates greater dominance in the communities during the rainy season and relative frequency shows the prevalence of species of the genus Glomus on all systems. The highest diversity, as measured by the Shannon- Wiener index, indicated that the soil under coconut had the highest values in both periods. There was a general increase in diversity comparing the rainy with the dry season. The dominance assessed by the Simpson index corroborates the results obtained by relative abundance, demonstrating that in the rainy season the concentration of dominance was higher in all systems. The similarity analysis using the Bray-Curtis index shows that the dry season has made the systems more similar, since they showed higher values in this period. Cluster analysis based on similarity index shows that despite the richness of abundance variations, the systems were also grouped in both periods. The soursop formed an isolated group, the area of forest was more similar to the old cashew culture. The other cluster was formed by the coconut culture and the new cashew plantation. Results of the study allowed concluding: agricultural activities have changed the community composition of AMF in relation to the native forest; the coconut agroecosystem had the highest biodiversity of AMF among all the systems evaluated; the species of the genus Glomus were the most abundant in agroecosystems and natural ecosystem; there were differences in community composition and diversity of fungi in between the rainy and dry season; and the diversity of AMF spores in soil did not correlate with the tropical fruit treeâs infective capacity.

Submitted by Claudia Rocha (claudia.rocha@udesc.br) on 2017-12-04T13:08:41Z No. of bitstreams: 1 PGCS15MA128.pdf: 1299017 bytes, checksum: c9080a00f46c534b9d0afc73165e1cb8 (MD5) / Made available in DSpace on 2017-12-04T13:08:41Z (GMT). No. of bitstreams: 1 PGCS15MA128.pdf: 1299017 bytes, checksum: c9080a00f46c534b9d0afc73165e1cb8 (MD5) Previous issue date: 2015-07-25 / Capes / Any inappropriate soil management, cause negative environmental impact on the diversity of soil fauna. This dissertation aimed to evaluate the influence of land use systems (LUS) on the morphological diversity of springtails, as well as its relationship with physical and chemical soil attributes. Were studied five LUS on the Plateau of Santa Catarina, Brazil: native forest (F), Eucalyptus plantation (Reu), perennial pasture (P), integrated crop-livestock (ILP) and no-tillage (PD), in two different seasons (winter and summer). The evaluation was performed by installing traps of type Pitfall traps per sampling grid (3 x 3). The same points were evaluated physical and chemical soil attributes. The morphotyping of the springtails consisted in observing five characteristics and each feature has been assigned a partial value of Eco-morphological index (EMI) for Biological Quality of Soil Index (QBS) modified. The data were subjected to multivariate analysis. In winter, the LUS (F) presented the highest abundance of morphotypes due the best values of Ca/Mg ratio, total organic carbon (TOC), bioporos, micropores and soil moisture in comparison to other LUS. ILP systems and PD already correlated with the Macropores. In the summer, again the F showed the highest abundance of morphotypes, however, the greatest diversity of levels of adaptation was found in PD. In summer, the F presented related to the TOC and micropores, while ILP and PD correlated with pH, bioporos and soil density. In winter, the value of QBS was greater in F, followed by Reu, P, PD and ILP, respectively, being smaller the higher the intensification of the LUS. In the summer, the QBS values were higher in F, followed by ILP, Reu, PD and P, respectively. The separation to the level of morphotypes proved an efficient alternative to indicate the level of intensification of land use, especially in combination with other explanatory environmental variables / Todo e qualquer manejo inadequado do solo, causa impacto ambiental negativo sobre a diversidade da fauna edáfica. A presente dissertação objetivou avaliar a influência de sistemas de uso e manejo do solo (SUS) sobre a diversidade morfológica de colêmbolos, bem como sua relação com atributos físicos e químicos do solo. Foram estudados cinco SUS no Planalto Catarinense, Brasil: floresta nativa (F), reflorestamento de eucalipto (Reu), pastagem perene (P), integração lavoura-pecuária (ILP) e plantio direto (PD), em duas épocas distintas (inverno e verão). A avaliação dos colêmbolos foi realizada instalando-se armadilhas do tipo Pitfall traps em um grid amostral (3 x 3). Nos mesmos pontos foram avaliados atributos físicos e químicos do solo. A morfotipagem dos colêmbolos consistiu na observação de cinco características e para cada característica foi atribuído um valor parcial do índice ecomorfológico (EMI) para a obtenção do Índice de Qualidade do Solo (QBS) modificado. Os dados foram submetidos a análises multivariadas. No inverno, o SUS F apresentou a maior abundância de morfotipos devido a melhores valores de relação Ca/Mg, carbono orgânico total (COT), bioporos, microporos e umidade do solo em comparação aos demais SUS. Já os sistemas ILP e PD se correlacionaram com o atributo macroporos. No verão, novamente a F apresentou maior abundância de morfotipos, porém, a maior diversidade de níveis de adaptação foi encontrada em PD. No verão, a F apresentou relação com o COT e microporos, enquanto ILP e PD se correlacionaram com pH, bioporos e densidade do solo. No inverno, o valor de QBS foi maior em F, seguido por Reu, P, PD e ILP, respectivamente, sendo menor quanto maior a intensificação do SUS. Já no verão, os valores de QBS foram maiores em F, seguido por ILP, Reu, PD e P, respectivamente. A separação ao nível de morfotipos se mostrou uma eficiente alternativa para indicar o nível de intensificação de uso do solo, principalmente em conjunto com outras variáveis ambientais explicativas

Globally land use change (LUC) with increasing in land use intensity has led to a decrease in soil organic matter (SOM). The reduction of soil C stock across LUC has been accompanied by a destabilization of soil structure and increases the soil erosion susceptibility. The destabilized soil structure is also concomitant with a loss of soil biodiversity and in particular, soil macroinvertebrate community. The focus of this dissertation is the effect of LUC with increasing in land use intensity on soil macrofauna, aggregation and SOM allocation. We hypothesized that LUC reduces soil macrofaunal biodiversity and consequently decreases soil engineering processes, resulting in destabilization of soil structure and impairing the ability of soil to physically protect SOM from decomposition inside stable aggregates, finally leading to depleted SOC stocks across LUC. In order to test these hypotheses, we conducted a field survey in 3 chronosequences of land use comprising native vegetation (NV), pasture (PA), and sugarcane crop (SC) in Central-Southern Brazil. This land use sequence provides a gradient of land use intensity and is projected to add 6.4 Mha of new sugarcane areas in Brazil by 2021. At each sampling point soil blocks of 25 X 25 cm and 5 x 5 cm to 10 cm depth were simultaneously collected from 0-10 cm, 10-20 cm, and 20-30 cm soil layers, for macrofauna isolation and aggregate fractionation, respectively. Within a radius of 6 meters around each sampling point, 12 subsamples were also collected from the same soil layers, and combined for total soil C and N concentration. An average reduction of 89% in the density of the soil macrofaunal community was observed when SC replaces PA, and a loss of 39% in the diversity of macrofauna groups. Our findings showed that, over a range of soil textures (16 - 66% clay), such biodiversity loss was strongly correlated with the destabilization of soil structure across LUC, whereas soil texture was not so. These observations consistently indicate that the abundance of detritivore soil animals, especially earthworms and termites, may be a significant predictor of soil structure transformations across LUC in tropical environments. Moreover, the sharp reduction in the abundance of earthworms was strongly positively correlated with the decrease in intra macroaggregate-associated C. As a result, after more than 20 years of sugarcane crop there were losses of 40 and 35% of C and N stocks, respectively, resulting in a rate of C emission of 1.3 Mg ha-1 yr-1. This C loss primarily occurred in the macroaggregate-associated C, as a result of the faster macroaggregate turnover under SC. In summary, the results presented here provide a mechanistic explanation as to why there is soil C depletion when increasing land use intensity in tropical soils: the huge reduction in the abundance of soil engineering invertebrates after LUC impair the ability of soil to physically protect SOM from decomposition inside stable aggregates, and therefore it is a primary mechanism controlling the soil C stocks\' depletion across LUC. / Globalmente mudanças no uso da terra (MUT) com o aumento da intensidade de uso do solo têm levado a uma diminuição da matéria orgânica do solo (MOS). A redução do estoque de C do solo após MUT tem sido acompanhada por uma desestabilização da estrutura do solo e aumento da susceptibilidade a erosão. A desestabilização da estrutura também é concomitante com a perda da biodiversidade do solo e, em particular, da comunidade de macroinvertebrados do solo. O foco deste trabalho é o efeito de MUT com aumento na intensidade de uso do solo sobre a macrofauna do solo, agregação e alocação da MOS. Nossa hipótese é que MUT reduz a diversidade da macrofauna do solo e, conseqüentemente, diminui os processos de engenharia de solo, resultando na desestabilização da estrutura do solo e prejudicando a capacidade do solo para proteger fisicamente a MOS da decomposição dentro de agregados estáveis, finalmente levando a redução dos estoques de C após MUT. Foi realizada uma pesquisa em 3 cronosseqüências de uso da terra que compreendem vegetação nativa (NV), pastagem (PA), e cana-de-açúcar (CA) na região Centro-Sul do Brasil. Esta MUT fornece um gradiente de intensidade de uso do solo e é projetada para adicionar 6,4 Mha de novas áreas de CA no Brasil até 2021. Em cada ponto de amostragem de solo blocos de 25 x 25 cm e 5 x 5 cm a 10 cm de profundidade foram coletados simultaneamente das camadas 0-10 cm, 10-20 cm e 20-30 cm de solo, para isolamento da macrofauna e fracionamento de agregados, respectivamente. Foi observada uma redução média de 89% na densidade da comunidade da macrofauna quando CA substitui PA, e uma perda de 39% da diversidade de grupos. Nossos resultados mostraram que, em um intervalo de texturas do solo (16-66% de argila), tal perda de biodiversidade foi fortemente correlacionada com a desestabilização da estrutura do solo após MUT. Estas observações indicam consistentemente que a abundância de animais detritívoros, especialmente minhocas e cupins, pode ser um preditor significativo de transformações da estrutura do solo em MUT. Além disso, a forte redução na abundância de minhocas foi fortemente e positivamente correlacionada com a diminuição do C alocado intra macroagregados. Como resultado, após mais de 20 anos de cultura de CA houve perdas de 40 e 35% dos estoques de C e N, respectivamente, resultando em uma taxa de emissão de C de 1,3 Mg ha-1 ano-1. Esta perda de C ocorreu principalmente no C associado aos macroagregados, como um resultado da reciclagem mais rápida dos macroagregados sob CA. Em resumo, os resultados aqui apresentados fornecem uma explicação mecanicista a respeito de porque há esgotamento do C do solo quando aumenta-se a intensidade de uso do solo em ambientes tropicais: a enorme redução na abundância de invertebrados \"engenheiros do solo\" após MUT prejudica a capacidade do solo para proteger fisicamente a MOS da decomposição dentro de agregados estáveis, e, portanto, é um mecanismo primário controlando a redução dos estoques de C no solo relacionada a MUT.

Globally land use change (LUC) with increasing in land use intensity has led to a decrease in soil organic matter (SOM). The reduction of soil C stock across LUC has been accompanied by a destabilization of soil structure and increases the soil erosion susceptibility. The destabilized soil structure is also concomitant with a loss of soil biodiversity and in particular, soil macroinvertebrate community. The focus of this dissertation is the effect of LUC with increasing in land use intensity on soil macrofauna, aggregation and SOM allocation. We hypothesized that LUC reduces soil macrofaunal biodiversity and consequently decreases soil engineering processes, resulting in destabilization of soil structure and impairing the ability of soil to physically protect SOM from decomposition inside stable aggregates, finally leading to depleted SOC stocks across LUC. In order to test these hypotheses, we conducted a field survey in 3 chronosequences of land use comprising native vegetation (NV), pasture (PA), and sugarcane crop (SC) in Central-Southern Brazil. This land use sequence provides a gradient of land use intensity and is projected to add 6.4 Mha of new sugarcane areas in Brazil by 2021. At each sampling point soil blocks of 25 X 25 cm and 5 x 5 cm to 10 cm depth were simultaneously collected from 0-10 cm, 10-20 cm, and 20-30 cm soil layers, for macrofauna isolation and aggregate fractionation, respectively. Within a radius of 6 meters around each sampling point, 12 subsamples were also collected from the same soil layers, and combined for total soil C and N concentration. An average reduction of 89% in the density of the soil macrofaunal community was observed when SC replaces PA, and a loss of 39% in the diversity of macrofauna groups. Our findings showed that, over a range of soil textures (16 - 66% clay), such biodiversity loss was strongly correlated with the destabilization of soil structure across LUC, whereas soil texture was not so. These observations consistently indicate that the abundance of detritivore soil animals, especially earthworms and termites, may be a significant predictor of soil structure transformations across LUC in tropical environments. Moreover, the sharp reduction in the abundance of earthworms was strongly positively correlated with the decrease in intra macroaggregate-associated C. As a result, after more than 20 years of sugarcane crop there were losses of 40 and 35% of C and N stocks, respectively, resulting in a rate of C emission of 1.3 Mg ha-1 yr-1. This C loss primarily occurred in the macroaggregate-associated C, as a result of the faster macroaggregate turnover under SC. In summary, the results presented here provide a mechanistic explanation as to why there is soil C depletion when increasing land use intensity in tropical soils: the huge reduction in the abundance of soil engineering invertebrates after LUC impair the ability of soil to physically protect SOM from decomposition inside stable aggregates, and therefore it is a primary mechanism controlling the soil C stocks\' depletion across LUC. / Globalmente mudanças no uso da terra (MUT) com o aumento da intensidade de uso do solo têm levado a uma diminuição da matéria orgânica do solo (MOS). A redução do estoque de C do solo após MUT tem sido acompanhada por uma desestabilização da estrutura do solo e aumento da susceptibilidade a erosão. A desestabilização da estrutura também é concomitante com a perda da biodiversidade do solo e, em particular, da comunidade de macroinvertebrados do solo. O foco deste trabalho é o efeito de MUT com aumento na intensidade de uso do solo sobre a macrofauna do solo, agregação e alocação da MOS. Nossa hipótese é que MUT reduz a diversidade da macrofauna do solo e, conseqüentemente, diminui os processos de engenharia de solo, resultando na desestabilização da estrutura do solo e prejudicando a capacidade do solo para proteger fisicamente a MOS da decomposição dentro de agregados estáveis, finalmente levando a redução dos estoques de C após MUT. Foi realizada uma pesquisa em 3 cronosseqüências de uso da terra que compreendem vegetação nativa (NV), pastagem (PA), e cana-de-açúcar (CA) na região Centro-Sul do Brasil. Esta MUT fornece um gradiente de intensidade de uso do solo e é projetada para adicionar 6,4 Mha de novas áreas de CA no Brasil até 2021. Em cada ponto de amostragem de solo blocos de 25 x 25 cm e 5 x 5 cm a 10 cm de profundidade foram coletados simultaneamente das camadas 0-10 cm, 10-20 cm e 20-30 cm de solo, para isolamento da macrofauna e fracionamento de agregados, respectivamente. Foi observada uma redução média de 89% na densidade da comunidade da macrofauna quando CA substitui PA, e uma perda de 39% da diversidade de grupos. Nossos resultados mostraram que, em um intervalo de texturas do solo (16-66% de argila), tal perda de biodiversidade foi fortemente correlacionada com a desestabilização da estrutura do solo após MUT. Estas observações indicam consistentemente que a abundância de animais detritívoros, especialmente minhocas e cupins, pode ser um preditor significativo de transformações da estrutura do solo em MUT. Além disso, a forte redução na abundância de minhocas foi fortemente e positivamente correlacionada com a diminuição do C alocado intra macroagregados. Como resultado, após mais de 20 anos de cultura de CA houve perdas de 40 e 35% dos estoques de C e N, respectivamente, resultando em uma taxa de emissão de C de 1,3 Mg ha-1 ano-1. Esta perda de C ocorreu principalmente no C associado aos macroagregados, como um resultado da reciclagem mais rápida dos macroagregados sob CA. Em resumo, os resultados aqui apresentados fornecem uma explicação mecanicista a respeito de porque há esgotamento do C do solo quando aumenta-se a intensidade de uso do solo em ambientes tropicais: a enorme redução na abundância de invertebrados \"engenheiros do solo\" após MUT prejudica a capacidade do solo para proteger fisicamente a MOS da decomposição dentro de agregados estáveis, e, portanto, é um mecanismo primário controlando a redução dos estoques de C no solo relacionada a MUT.

This thesis presents the findings of an investigation of the spatial and temporal distribution of soil macrofauna at multiple scales within smallholder agriforestry fields in a remote, mountainous area of western Honduras. Since 1990, smallholder farmers in the study area have switched from traditional slash-and-burn agriculture to a form of slash-and-mulch agriforestry based on cultivating maize, beans and sorghum amongst dispersed trees. The principal objective was to examine the influence of the slash-and-mulch agricultural system on soil macrofauna abundance, biomass and community composition, and relate soil macrofauna distribution patterns to environmental variables. The initial stage of the research comprised transect-based sampling of soil macrofauna and biophysical variables in four common land uses of the study area. All four land uses (secondary forest, young milpa (agriforestry), mature milpa, and pasture) supported abundant, diverse and heterogeneous soil macrofauna communities, with few notable differences in soil macrofauna distribution among land uses. The most abundant soil macrofauna taxa were termites, ants, earthworms and beetles. Of the 'explanatory' environmental variables that were measured (including land use and selected soil properties, vegetation characteristics and topographic variables), those that had the strongest relationships with soil macrofauna abundance were land use, tree density and soil organic matter content. The second stage of the research was spatially-orientated and used stratified sampling based on within-field differences in farmer-defined soil type, as well as grid-based sampling of soil macrofauna surface activity. There was substantial within-field variation in soil type and topography, which was related to distribution patterns of at least one agriculturally-important soil macrofauna taxon. Earthworm activity was higher in areas of fertile soil and lower slope positions. At a finer scale, there was a positive spatial correlation between tree distribution and earthworm casting activity. The final phase situated the biophysical research in the local socio-economic context through participant observation and interviews with farmers. The results of the three phases of the study were incorporated into an original conceptual model of the relationships among soil macrofauna and environmental variables in the study area across multiple spatial scales and along a chronosequence of land use changes. Specific pointers are provided for further research on the role of soil fauna in influencing soil structure, nutrient cycling and pest species abundance, and for further investigating local knowledge and the socio-economic and cultural drivers of land use change.

De nombreuses études mettent en évidence un effet positif de la diversité spécifique sur la productivité des communautés végétales et la biodiversité associée. Mais l’effet de la diversité génétique sur la communauté d’espèces reste encore peu étudié en dépit des rares études montrant un effet positif avec des perspectives d’application dans le domaine de l’amélioration des plantes. C’est dans ce contexte que cette thèse s’interroge sur l’effet de la diversité génétique sur les communautés prairiales et la biodiversité du sol associée. Cette thèse repose sur une situation réelle via un dispositif d’évaluation de mélanges prairiaux installé par et chez un sélectionneur de plantes fourragères. Les résultats majeurs de cette thèse sont un effet positif de la diversité génétique des espèces sur la production de biomasse du mélange, particulièrement lors d’épisodes de sècheresse, et sur l’équilibre d’abondance des espèces. Ces effets positifs semblent être le résultat d’une différenciation de niches des espèces qui est à la base de la complémentarité des espèces en écologie. Il a été mis en évidence une complémentarité temporelle des espèces par une asynchronie des dynamiques de croissance, mais aussi une complémentarité sur l’acquisition de la lumière par des mécanismes de sélection et de plasticité. Enfin, des effets de la diversité génétique ont été observés sur la diversité microbienne avec des rétroactions potentielles sur les plantes. Au vu de ces résultats, il apparait que la diversité génétique occupe une place centrale dans l’assemblage et la structuration des communautés végétales et microbiennes, nous amenant à réfléchir quant à sa valorisation en amélioration des plantes. / Many studies highlight a positive effect of species diversity on plant community productivity and associated biodiversity. But genetic diversity effect on species community is still poorly studied despite the rare studies showing a positive effect with prospects for application in the field of plant breeding. It is in this context that this thesis examines the genetic diversity effect on grassland communities and associated soil biodiversity. This thesis is based on a real situation via an evaluation design of grassland mixtures installed by and in a plants breeding company. The major results of this thesis are a positive effect of the species genetic diversity on mixture biomass production, especially during drought episodes, and on species abundance equilibrium. These positive effects seem to be the result of a niche differentiation of species which is at the basis of species complementarity in ecology. Temporal complementarity of species has been demonstrated by asynchronous growth dynamics, but also by a complementarity for light acquisition via selection and plasticity mechanisms. Finally, genetic diversity effects have been observed on microbial diversity with plants feedbacks. In view of these results, it appears that genetic diversity occupies a central role in the assembly and structure of plant and microbial communities, leading us to consider how it could be integrated into plant breeding program.