Tropical forests restoration is an important tool for climate change mitigation and biodiversity conservation. We can ally both of these elements, according to the biodiversity and ecosystem (BEF) functioning theory, which says that diversity enhances ecosystem functions, as primary productivity. Nevertheless, the greatest part of BEF studies up to very recently have focused on grasslands and not on as complex ecosystems as tropical forests. It is necessary to better understand above- and below-ground processes through which biodiversity acts on ecosystem functions. This work aimed to investigate effects of tree richness on both above- and below-ground ecological processes. It was based on two tropical forests undergoing restoration, in Sardinilla (Panama) and in Anhembi (Brazil). The former was especially designed for BEF studies and allowed to untangle effects of biodversity on ecosystem functions. The latter had more than a hundred species in plots and permitted investigation of the effects of high tree richness levels. In both Sardinilla and Anhembi, we investigated if tree richness levels affected an above-ground ecological process, light interception, and which mechanisms could be related to it. Richness could enhance light interception and mechanisms as spatial (horizontal and vertical) and temporal light distribution. It promoted both selection and complementarity effects. In Anhembi, we investigated if species richness influenced below-ground processes related to soil carbon stocks. Stand richness enhanced fine root production and stock. Effects of stand number of species on litter decomposition and stock were not linear. Richness of litter content, however, did not affect its decomposition rates. Number of stand species did not influence litter production. Differences of litter production, stock and fine root production among distinct richness levels did not change over the time. However, distribution of fine roots over the space, within different layers of soil, was affected by number of tree species. We concluded that even very high richness levels could not saturate some of the ecological processes studied. Diversity acted on both above- and below-ground processes, in various and sometimes opposite ways, counting on multi-direction feedbacks. It is very important to understand these mechanisms in order to potencialize biodiversity convervation and carbon sequestration by tropical forest restoration. Future studies may focus on untangling effects of diversity on below-ground processes (which have not been exhaustively explored in research), on understanding how high diversity levels affects natural regeneration and on investigationg functional traits provided by different species. / A restauração de florestas tropicais é uma importante ferramenta para a mitigação de mudanças climáticas e conservação de biodiversidade. Essas duas medidas podem ser aliadas, de acordo com a teoria de biodiversidade e funcionamento de ecossistemas (BEF, do inglês: biodiversity and ecosystem functioning), segundo a qual a diversidade pode favorecer funções do ecossistema, como a produtividade primária. Entretanto, a maior parte dos estudos de BEF até muito recentemente focaram em campos de gramíneas e não em ecossistemas tão complexos quanto florestas tropicais. É necessário entender tanto processos acima quanto abaixo do solo pelos quais a biodiversidade atua no funcionamento de ecossistemas. Este trabalho teve como objetivo verificar o efeito da riqueza de espécies arbóreas em processes ecológicos acima e abaixo do solo. Ele se baseou em duas áreas de estudo, em Sardinilla (Panamá) e em Anhembi (Brasil). A primeira foi especialmente projetada para estudos de BEF e permitiu destrinchar efeitos da biodiversidade em funções do ecossistema. A segunda possuía parcelas com mais de cem espécies, permitindo explorar os efeitos de altos níveis de riqueza. Tanto em Sardinilla quanto em Anhembi, investigamos se a riqueza de espécies arbóreas influenciou um processo ecológico acima do solo, a interceptação de luz, bem como mecanismos que podem estar associados a ele. A riqueza de espécies aumentou a interceptação de luz pelo dossel e estimulou mecanismos como a distribuição de luz ao longo do espaço (horizontal e vertical) e tempo. Ela promoveu tanto efeito de seleção quanto de complementaridade. Na área de Anhembi, investigamos se a riqueza de espécies influenciou processes abaixo do solo relacionados ao estoque de carbono nesse compartimento. A riqueza no dossel aumentou a produção e o estoque de raízes finas. Número de espécies do dossel teve efeito não linear sobre taxas de decomposição e estoque de serapilheira. A riqueza do conteúdo da serapilheira, contudo, não influenciou sua decomposição. O número de espécies do dossel também não influenciou a produção de serapilheira. As diferenças de produção e estoque de serapilheira e de produção de raízes finas, entre diferentes níveis de riquezas, não se alteraram ao longo do tempo. Contudo, o número de espécies arbóreas promoveu maior distribuição de raízes finas em diferentes camadas do solo. Concluímos que elevados níveis de riqueza não saturaram alguns processes ecológicos estudados. A diversidade foi capaz de atuar em processos tanto acima quanto abaixo do solo, por vários meios, muitas vezes em sentidos opostos, contando com feedbacks multidirecionais. É muito importante entender esses mecanismos para potencializar a conservação da biodiversidade e a provisão de funções ecossistêmicas, no processo de restauração de florestas tropicais, em um contexto internacional de necessidade de mitigação de mudanças climáticas. Estudos futuros devem focar em efeitos da diversidade em processos abaixo do solo (que são os menos abordados em estudos até o momento), em entender como altos níveis de diversidade podem afetar a regeneração natural em florestas e em explorar os atributos funcionais apresentados por cada espécie.

O equilíbrio ecológico dos ecossistemas aquáticos é fundamental para a conservação da biodiversidade e para que tais ambientes possam desempenhar seus serviços ambientais. O metabolismo dos riachos pode ser utilizado como um indicador funcional do nível de perturbação do ambiente, devido à influência das condições da bacia hidrográfica sobre as características e estrutura dos ecossistemas aquáticos. A presente pesquisa avaliou a variação espaço-temporal das taxas de produção primária bruta (PPB) e respiração (R) em riachos localizados no Cerrado, como subsídio para o entendimento da influência de algumas características da água, do substrato e da vegetação ripária sobre o seu metabolismo. Para isso, foram estudados seis riachos em ambientes subtropicais (São Carlos e Brotas, SP, Brasil) com diferentes condições ambientais. O metabolismo foi modelado pelas mudanças de curto prazo nas concentrações de oxigênio dissolvido (OD) e da radiação solar fotossinteticamente ativa, a cada 10 min em períodos de 24h. Além disso, a modelagem considerou o coeficiente de reaeração em cada riacho, que foi estimado por meio de traçador gasoso (SF6). Foram determinadas variáveis de qualidade da água, hidrológicas, do substrato e porcentagem de cobertura vegetal. Modelos de regressão foram utilizados, entre outras análises estatísticas, para avaliar as principais variáveis preditoras das taxas metabólicas. Os riachos apresentaram vazões sempre inferiores a 100 L.s-1, e a porcentagem de cobertura vegetal variou entre 39 e 86%. As concentrações médias de nitrogênio e fósforo totais variaram entre 0,8-1,3 mg.L-1 e 9,4-42,4 μg.L-1, respectivamente, sendo os riachos classificados entre oligo e mesotróficos. A amplitude média das variações diárias de OD foi de 0,2 a 1,2 mg.L-1. As taxas de PPB apresentaram variação de 0,01 a 0,68 gO2 m-2.dia-1. Já as taxas de R variaram entre 0,61-42,08 gO2 m-2.dia-1. A partir do balanço entre a PPB e a R, os seis riachos apresentaram condições heterotróficas (respiração excedeu a produção primária bruta, com a produção primária líquida negativa), o que torna esses ambientes mais vulneráveis ao eventual aporte de cargas orgânicas que gerem demanda por oxigênio. Embora as concentrações de fósforo tenham sido correlacionadas com as taxas metabólicas, as principais variáveis preditoras, pelos modelos de regressão, foram vazão e a porcentagem de cobertura vegetal. A cobertura vegetal provavelmente foi responsável pela redução da incidência de radiação solar e, consequentemente, o principal limitante da disponibilidade de luz subaquática para algas bentônicas. A vazão apresentou possível efeito na redução da biomassa de algas pela abrasão decorrente da velocidade da água. Espera-se que, além de gerarem um conjunto de dados sobre ambientes aquáticos de um bioma ainda relativamente pouco estudado, o Cerrado, as informações apresentadas sobre os principais fatores intervenientes nos processos metabólicos dos riachos possam oferecer direcionamentos a projetos para sua conservação e para a manutenção de seus serviços ambientais. / The ecological balance of aquatic ecosystems is fundamental for biodiversity conservation and for to perform the environmental services. Stream metabolism can be used as a functional indicator of the level of disturbance of the environment due to the influence of watershed conditions on the characteristics and structure of aquatic ecosystems. The present study evaluated the spatial-temporal variation of gross primary production (GPP) and ecosystem respiration (R) rates, in streams located in the Cerrado, as to understanding the influence of water and the substrate characteristics and vegetation in metabolism. For this, six subtropical streams (São Carlos and Brotas, SP, Brazil) were studied with different environmental conditions. The metabolism was modeled by the short-term changes in the concentrations of dissolved oxygen (DO) and the photosynthetically active solar radiation, every 10 min in periods of 24h. In addition, the modeling considers the reaeration rates in each stream, which was estimated by gas tracer (SF6). Variables of water quality, substrate, hydrological characteristics, and percentage of canopy cover were determined. Regression models were used, among other statistical analyzes, to evaluate the main predictors of metabolic rates. The streams had discharge rates lower than 100 L.s-1, and the percentage of canopy cover varied between 39 and 86%. The mean concentrations of nitrogen and phosphorus varied between 0.8-1.3 mg.L-1 and 9.4-42.4 μg.L-1, respectively, and the streams were classified as oligo and mesotrophic. The mean amplitude of daily DO variations was 0.2 to 1.2 mg.L-1. Rates of GPP ranged from 0.01 to 0.68 gO2 m-2.day-1. R rates varied from 0.61 to 42.08 gO2 m-2.day-1. From the balance between PPB and R, the six streams presented heterotrophic conditions (respiration exceeded gross primary production, with negative net primary production), which makes these streams more vulnerable to the eventual contribution of organic loads that generate demand for oxygen. Although phosphorus concentrations were correlated with metabolic rates, the main predictors of metabolic rates, by regression models, were discharge and canopy cover percentage. The canopy cover was probably responsible for reducing the incidence of solar radiation and, consequently, the main limitation of the availability of underwater light for benthic algae. The discharge indicated a possible effect on the algae biomass reduction due to the abrasion caused by the water velocity. It is expected that, in addition to the generation of data set on aquatic environments of the relatively little studied biome, the Cerrado, the information presented about the main drivers in the metabolic processes of the streams can offer directions to projects for its conservation and for the support of their environmental services.

Diversos estudos teóricos, experimentais e observacionais têm demonstrado que as relações entre a biodiversidade e as funções ecossistêmicas (BEF) são determinadas pela estrutura funcional da comunidade (ou seja, pela distribuição dos atributos das suas espécies constituintes). Isso pode ocorrer por meio de dois mecanismos mutuamente não exclusivos: (1) a hipótese de dominância (também denominada de efeito de relação de massa), na qual os processos ecossistêmicos são influenciados pela média ponderada na comunidade de um dado atributo funcional (CWM) considerado relevante; (2) a hipótese de complementaridade, na qual a maior variabilidade de um atributo funcional na comunidade (FD) é uma expressão da complementariedade de nicho, o que beneficia o desempenho dos processos ecossistêmicos. Embora ambos os mecanismos já tenham sido amplamente estudados em comunidades de plantas em pequenas escalas espaciais, análises globais considerando distintos biomas ainda são necessárias. Neste estudo, a relação entre biodiversidade e funcionamento dos ecossistemas foi avaliada com base na integração entre uma base de dados global de parcelas de vegetação (sPlot), uma base de dados de atributos de espécies de plantas (TRY) e dados do Índice de Vegetação por Diferença Normalizada (NDVI) obtidos por sensoriamento remoto. O objetivo foi verificar, simultaneamente, os efeitos de dominância e de complementaridade sobre a produção de biomassa vegetal em ecossistemas campestres em todo o mundo. Os dados sobre a estrutura funcional das comunidades (CWM e FD) foram obtidos a partir da base de dados sPLOT e TRY, utilizando para isso atributos funcionais de plantas ecologicamente relevantes. O NDVI, considerado como aproximação da produtividade da vegetação, representa uma medida do funcionamento do ecossistema e foi obtido a partir do produto MOD13Q do sensor MODIS, com resolução espacial de 250m. Para garantir que as medidas de NDVI fossem derivadas apenas de ecossistemas campestres, sem a interferência de outras fisionomias vegetais, foram descartadas as parcelas do sPlot com presença de paisagens heterogêneas no seu entorno mediante consulta a um mapa global de cobertura e uso da terra (Globcover2009). Para quantificar os efeitos independentes da dominância e da complementariedade sobre as variações no NDVI , com controle das variáveis climáticas, foi utilizada uma análise de regressão múltipla do tipo commonality. Os resultados demonstraram que o principal preditor da variação no NDVI correspondeu a um conjunto de atributos funcionais das espécies dominantes relacionados com o espectro de economia da comunidade vegetal (atributos fast-slow), indicando a prevalência da hipótese de dominância (R2 ajustado = 0,65). Os efeitos evidentes da dominância e os efeitos potenciais da complementariedade são discutidos no contexto da sua relação com os fatores abióticos, sendo que a precipitação pluviométrica, em particular, parece ter maior influência tanto sobre a composição de atributos quanto sobre a produtividade. Apesar de algumas limitações metodológicas, a abordagem inovadora utilizada neste trabalho pode ajudar a esclarecer as relações entre biodiversidade e funções ecossistêmicas em escala global, dentro de uma perspectiva integradora e baseada em dados. / Theoretical, experimental and observational studies show that biodiversity ecosystem functioning (BEF) relationships are determined by functional community structure (i.e. trait distributions in a community) through two mutually non-exclusive mechanisms: (1) The dominance hypothesis (a.k.a. mass ratio effect) links ecosystem processes to the community weighted mean (CWM) of a relevant effect trait. (2) The complementarity hypothesis states that higher variability of a trait value within a community (FD) reflects niche complementarity enhancing ecosystem processes. While both mechanisms have been extensively studied in plant communities at small spatial scales, there is a need for global analyses across biomes. Here, a data driven approach to the BEF question is presented integrating a global vegetation plot database with a trait database and remotely sensed NDVI. The objective of this study was to simultaneously evaluate dominance and complementarity effects in grassland systems worldwide. Data on functional community structure (CWM and FD) were obtained from the global vegetation plot database sPlot in combination with the plant trait database TRY using 18 ecologically relevant plant traits. Ecosystem functioning at the selected sPlot sites (n = 2941) was measured as NDVI at a spatial resolution of 250m using the MODIS product MOD13Q (annual peak NDVI being a proxy of productivity). The landcover map Globcover2009 was used for characterization of landscape heterogeneity and landcover at each site, and plots in heterogeneous non-grassland pixels were discarded. Multiple regression commonality analysis was used to disentangle the contributions of complementarity and dominance effects to the variation in NDVI, while controlling for climate variables (adjusted R2 = 0.65). The results show that a plant community economics spectrum referring to the “fast-slow traits” of the dominant species in the community was the strongest predictor of the NDVI values in the grassland systems (dominance effect). Both, evident dominance and potential complementarity effects are discussed against the background of their interplay with abiotic factors and it is noted that especially precipitation seems to drive trait composition and productivity. Despite methodological shortcomings, the novel approach presented in this paper is considered a step towards a more integrative data-driven BEF debate at the global scale

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.

O equilíbrio ecológico dos ecossistemas aquáticos é fundamental para a conservação da biodiversidade e para que tais ambientes possam desempenhar seus serviços ambientais. O metabolismo dos riachos pode ser utilizado como um indicador funcional do nível de perturbação do ambiente, devido à influência das condições da bacia hidrográfica sobre as características e estrutura dos ecossistemas aquáticos. A presente pesquisa avaliou a variação espaço-temporal das taxas de produção primária bruta (PPB) e respiração (R) em riachos localizados no Cerrado, como subsídio para o entendimento da influência de algumas características da água, do substrato e da vegetação ripária sobre o seu metabolismo. Para isso, foram estudados seis riachos em ambientes subtropicais (São Carlos e Brotas, SP, Brasil) com diferentes condições ambientais. O metabolismo foi modelado pelas mudanças de curto prazo nas concentrações de oxigênio dissolvido (OD) e da radiação solar fotossinteticamente ativa, a cada 10 min em períodos de 24h. Além disso, a modelagem considerou o coeficiente de reaeração em cada riacho, que foi estimado por meio de traçador gasoso (SF6). Foram determinadas variáveis de qualidade da água, hidrológicas, do substrato e porcentagem de cobertura vegetal. Modelos de regressão foram utilizados, entre outras análises estatísticas, para avaliar as principais variáveis preditoras das taxas metabólicas. Os riachos apresentaram vazões sempre inferiores a 100 L.s-1, e a porcentagem de cobertura vegetal variou entre 39 e 86%. As concentrações médias de nitrogênio e fósforo totais variaram entre 0,8-1,3 mg.L-1 e 9,4-42,4 μg.L-1, respectivamente, sendo os riachos classificados entre oligo e mesotróficos. A amplitude média das variações diárias de OD foi de 0,2 a 1,2 mg.L-1. As taxas de PPB apresentaram variação de 0,01 a 0,68 gO2 m-2.dia-1. Já as taxas de R variaram entre 0,61-42,08 gO2 m-2.dia-1. A partir do balanço entre a PPB e a R, os seis riachos apresentaram condições heterotróficas (respiração excedeu a produção primária bruta, com a produção primária líquida negativa), o que torna esses ambientes mais vulneráveis ao eventual aporte de cargas orgânicas que gerem demanda por oxigênio. Embora as concentrações de fósforo tenham sido correlacionadas com as taxas metabólicas, as principais variáveis preditoras, pelos modelos de regressão, foram vazão e a porcentagem de cobertura vegetal. A cobertura vegetal provavelmente foi responsável pela redução da incidência de radiação solar e, consequentemente, o principal limitante da disponibilidade de luz subaquática para algas bentônicas. A vazão apresentou possível efeito na redução da biomassa de algas pela abrasão decorrente da velocidade da água. Espera-se que, além de gerarem um conjunto de dados sobre ambientes aquáticos de um bioma ainda relativamente pouco estudado, o Cerrado, as informações apresentadas sobre os principais fatores intervenientes nos processos metabólicos dos riachos possam oferecer direcionamentos a projetos para sua conservação e para a manutenção de seus serviços ambientais. / The ecological balance of aquatic ecosystems is fundamental for biodiversity conservation and for to perform the environmental services. Stream metabolism can be used as a functional indicator of the level of disturbance of the environment due to the influence of watershed conditions on the characteristics and structure of aquatic ecosystems. The present study evaluated the spatial-temporal variation of gross primary production (GPP) and ecosystem respiration (R) rates, in streams located in the Cerrado, as to understanding the influence of water and the substrate characteristics and vegetation in metabolism. For this, six subtropical streams (São Carlos and Brotas, SP, Brazil) were studied with different environmental conditions. The metabolism was modeled by the short-term changes in the concentrations of dissolved oxygen (DO) and the photosynthetically active solar radiation, every 10 min in periods of 24h. In addition, the modeling considers the reaeration rates in each stream, which was estimated by gas tracer (SF6). Variables of water quality, substrate, hydrological characteristics, and percentage of canopy cover were determined. Regression models were used, among other statistical analyzes, to evaluate the main predictors of metabolic rates. The streams had discharge rates lower than 100 L.s-1, and the percentage of canopy cover varied between 39 and 86%. The mean concentrations of nitrogen and phosphorus varied between 0.8-1.3 mg.L-1 and 9.4-42.4 μg.L-1, respectively, and the streams were classified as oligo and mesotrophic. The mean amplitude of daily DO variations was 0.2 to 1.2 mg.L-1. Rates of GPP ranged from 0.01 to 0.68 gO2 m-2.day-1. R rates varied from 0.61 to 42.08 gO2 m-2.day-1. From the balance between PPB and R, the six streams presented heterotrophic conditions (respiration exceeded gross primary production, with negative net primary production), which makes these streams more vulnerable to the eventual contribution of organic loads that generate demand for oxygen. Although phosphorus concentrations were correlated with metabolic rates, the main predictors of metabolic rates, by regression models, were discharge and canopy cover percentage. The canopy cover was probably responsible for reducing the incidence of solar radiation and, consequently, the main limitation of the availability of underwater light for benthic algae. The discharge indicated a possible effect on the algae biomass reduction due to the abrasion caused by the water velocity. It is expected that, in addition to the generation of data set on aquatic environments of the relatively little studied biome, the Cerrado, the information presented about the main drivers in the metabolic processes of the streams can offer directions to projects for its conservation and for the support of their environmental services.

The relationship between biodiversity and ecosystem functioning is important in maintaining agroecosystem sustainability. Plant-microbe symbioses, such as exists between the grass tall fescue (Schedonorus arundinaceum) and the asexual fungal endophyte Epichloë coenophiala, can be utilized to enhance agroecosystem functions, such as herbivore resistance. “Novel” E. coenophiala strains that vary in the production of mammal- and insect-toxic compounds have been identified, inserted into tall fescue cultivars, and are planted in pastures globally. Novel fungal endophyte-tall fescue associations may have divergent ecosystem function effects. This study assessed effects of different fescue-endophyte symbiotic combinations on pasture ecosystem function, including aboveground (fescue biomass, plant species richness, alkaloid synthesis, arthropod abundance) and belowground (soil microbial biomass, soil enzyme activity, trace gas fluxes) parameters. Results showed no significant effects of increasing symbiotic diversity within a fescue stand on aboveground measurements, bar arthropod abundance and alkaloid synthesis. Most soil parameters quantified had significant symbiotic diversity effects. For example, soil microbial biomass decreased whereas soil enzyme activity increased with increasing symbiotic diversity. Overall, our results suggested that increasing symbiotic diversity had weak to moderate effects on aboveground processes and stronger effects on certain belowground processes, indicating that symbiotic diversity can impact ecosystem functions and warrants further research.

<p>Heterotrophic bacteria utilize dissolved organic matter, and the carbon flow through an ecosystem depends on the fractions of the utilized carbon that is either respired or transferred to higher trophic levels. The major aim this thesis is to investigate 1) the relationship between composition and functioning in heterotrophic bacterioplankton communities and 2) the influence of environmental conditions on both parameters. I set up several batch culture experiments, where lake water filtrates containing bacteria but no grazers were inoculated into sterile freshwater medium to investigate the importance of the origin of the source community (the inoculum) versus the environmental conditions (the medium) for the composition and functional performance of bacterial communities. In some experiments the medium was manipulated to simulate changes in salinity, pH and dissolved organic matter quantity and quality. Functional parameters (biomass yield, respiration, growth efficiency and enzyme activities) and the genetic composition of the emerging bacterial communities were determined.</p><p>When bacterial inocula obtained from different habitats were re-grown under identical conditions, differently composed communities emerged. This indicates that the history and distribution of taxa within the inoculum was an important regulating factor of community composition. The coupling between community composition and functioning was not very tight, and there was functional equivalency with respect to aggregated functions important at the ecosystem scale (e.g., biomass production and respiration). The functional performance of bacterial communities could to a large extent be predicted from the medium alone, except when it deviated strongly from the ambient settings. When bacterial communities were exposed to dilution, a strong change in pH or an increase in salinity, growth of structurally and functionally distinct communities occurred. I therefore suggest that it depends on the disturbance regime how bacterial community structure and function are related to each other. </p>

Heterotrophic bacteria utilize dissolved organic matter, and the carbon flow through an ecosystem depends on the fractions of the utilized carbon that is either respired or transferred to higher trophic levels. The major aim this thesis is to investigate 1) the relationship between composition and functioning in heterotrophic bacterioplankton communities and 2) the influence of environmental conditions on both parameters. I set up several batch culture experiments, where lake water filtrates containing bacteria but no grazers were inoculated into sterile freshwater medium to investigate the importance of the origin of the source community (the inoculum) versus the environmental conditions (the medium) for the composition and functional performance of bacterial communities. In some experiments the medium was manipulated to simulate changes in salinity, pH and dissolved organic matter quantity and quality. Functional parameters (biomass yield, respiration, growth efficiency and enzyme activities) and the genetic composition of the emerging bacterial communities were determined. When bacterial inocula obtained from different habitats were re-grown under identical conditions, differently composed communities emerged. This indicates that the history and distribution of taxa within the inoculum was an important regulating factor of community composition. The coupling between community composition and functioning was not very tight, and there was functional equivalency with respect to aggregated functions important at the ecosystem scale (e.g., biomass production and respiration). The functional performance of bacterial communities could to a large extent be predicted from the medium alone, except when it deviated strongly from the ambient settings. When bacterial communities were exposed to dilution, a strong change in pH or an increase in salinity, growth of structurally and functionally distinct communities occurred. I therefore suggest that it depends on the disturbance regime how bacterial community structure and function are related to each other.

Climate change has created potential major threats to global biodiversity. The multiple components of climate change are projected to affect all pillars of biodiversity, from genes over species to biome level. Of particular concerns are "tipping points" where the exceedance of ecosystem thresholds will possibly lead to irreversible shifts of ecosystems and their functioning. As biodiversity underlies all goods and services provided by ecosystems that are crucial for human survival and wellbeing, this paper presents potential effects of climate change on biodiversity, its plausible impacts on human society as well as the setting in addressing a global crisis. Species affected by climate change may respond in three ways: change, move or die. Local species extinctions or a rapidly affected ecosystem as a whole respectively might move toward its particular "tipping point", thereby probably depriving its services to human society and ending up in a global crisis. Urgent and appropriate actions within various scenarios of climate change impacts on biodiversity, especially in tropical regions, are needed to be considered. Foremost a multisectoral approach on biodiversity issues with broader policies, stringent strategies and programs at international, national and local levels is essential to meet the challenges of climate change impacts on biodiversity.

Species diversity may simultaneously be a cause and a consequence of variability in population, community and ecosystem properties. Ecology has traditionally focused on elucidating the causes of biodiversity. However, in the last decade and a half ecologists have asked the opposite question: What are the consequences of species diversity? The majority of these studies elucidated the effects of species diversity within single trophic levels. Incorporating trophic complexity is the next step in this research program. In this dissertation I investigated the causes of resource species diversity, as well as the impacts that resource diversity has on rates of consumption and the stability of population, community and ecosystem properties over time in planktonic food webs. The high diversity of phytoplankton found in nature appears to defy the competitive exclusion principle, and elucidating the mechanisms which maintain this diversity continues to be a challenge. In general, variability in limiting factors is required to maintain non-neutral species diversity, but this variability can be generated by forces outside of the competitive community (i.e. exogenous), or may be the outcome of competitive interactions themselves (i.e. endogenous). Using microcosm experiments, I showed that endogenously generated variability in limiting factors was more effective at maintaining phytoplankton species diversity over the long-term, although the strength of this effect depended on the composition of the phytoplankton community. Existing resource diversity has been proposed to generally weaken consumer-resource interaction strengths and limit consumer control of resource biomass. This is because more diverse resource communities are more likely to contain inedible, unpalatable, toxic or non-nutritious species. However, when resource communities contain multiple palatable species, diversity may also accelerate consumption. Using grazing experiments with multiple zooplankton consumer species, I found that the mechanism, direction and magnitude of modulation of consumption depended on the feeding selectivity of the consumer and the composition of the resource community. By altering consumer-resource interaction strengths in the short-term, resource species diversity may impact the stability of consumer-resource dynamics in the long-term. In separate microcosm experiments, I investigated the influence of resource species diversity, community composition and consumer feeding selectivity on population, community, and ecosystem properties over time. Diversity had positive effects on phytoplankton population biomass, resource community biomass, the rate of photosynthesis, the standing stock of particulate nutrients, and the generalist consumer’s population density. It also stabilized resource community biomass and the stocks of particulate nutrients over time. Unexpectedly, diversity did not stabilize either of the consumer populations, regardless of feeding selectivity. This suggests that effects of diversity on resource community properties do not impact consumer dynamics linearly. Resource community composition was generally more important than resource species diversity in determining food web properties. The importance of community composition in determining both the causes and consequences of resource diversity in these experiments points to the importance of species’ traits and the outcomes of their interactions. I suggest that the use of complex adaptive systems theory and trait-based approaches in the future will allow a consideration of the feedbacks between the causes and consequences of species diversity in food webs. / Graduate