Headwaters are crucial linkages between upland ecosystems and navigable waterways, serving as important sources of water, sediment, energy, nutrients and invertebrate prey for downstream ecosystems. Surface coal mining in central Appalachia impacts headwaters by burying streams and introducing pollutants to remaining streams including excessive sediments, trace elements, and salinity. Benthic macroinvertebrates are widely used as indicators of biological conditions of streams and are frequently sampled using semi-quantitative methods that preclude calculations of areal densities. Studies of central Appalachian mining impacts in non-acidic streams often focus on biotic effects of salinity, but other types of pollution and habitat alteration can potentially affect benthic macroinvertebrate community (BMC) structure and perhaps related functions of headwater streams. Objectives were: 1) use quantitative sampling and enumeration to determine how density, richness, and composition of BMCs in non-acidic central Appalachian headwaters respond to elevated salinity caused by coal surface mining, and 2) determine if BMC structural differences among study streams may be attributed to habitat and water-quality effects in addition to elevated salinity. I analyzed BMC structure, specific conductance (SC, surrogate measure of salinity), and habitat-feature data collected from 15 streams, each visited multiple times during 2013-2014. BMC structure changed across seasonal samples. Total benthic macroinvertebrate densities did not appear to be impacted by SC during any months, but reduced densities of SC-sensitive taxa were offset by increased densities of SC-tolerant taxa in high-SC streams. Total richness also declined with increasing SC, whereas BMCs in high-SC streams were simplified and dominated by a few SC-tolerant taxa. Taxonomic replacement was detected in high-SC streams for groups of benthic macroinvertebrates that did not exhibit density or richness response, showing that taxonomic replacement could be a valuable tool for detecting BMC changes that are not evident from analyses using conventional metrics. Specific conductance, water-column selenium concentration, large-cobble-to-fines ratio of stream substrate, and relative bed stability were associated with changes in BMC structure. These results suggest multiple stressors are influencing BMCs in mining-influenced Appalachian streams. These findings can inform future management of headwater streams influenced by mining in central Appalachia. / Ph. D. / Humans rely on headwater streams to provide water of sufficient quantity and quality for use in fishing, swimming, and other designated purposes. In central Appalachia USA, surface coal mining impacts headwaters by burying streams and introducing various types of pollutants to remaining streams. Benthic macroinvertebrates, primarily stream insects, are widely used as indicators of stream-water quality because responses by certain groups of benthic macroinvertebrates to types and levels of pollution are known. Studies of central Appalachian coal mining impacts in non-acidic streams often focus on the effects of elevated salinity on benthic macroinvertebrate community (BMC) structure; however, other types of pollution and habitat alteration can also potentially affect BMC structure. Study objectives were to determine how BMCs in central Appalachian headwaters responded to elevated salinity caused by coal surface mining, and to determine if BMC structure differences among study streams may be caused by habitat and water-quality effects other than elevated salinity. I analyzed BMC, salinity, and habitat data collected from 15 streams, each visited up to six times during 2013-2014. I found that BMC structures varied seasonally, likely caused by natural life cycle variation of benthic macroinvertebrates. Streams in watersheds impacted by more areal coal mining disturbance tended to have higher levels of salinity, water selenium concentrations, and fine sediments, and fewer types of benthic macroinvertebrates although total BMC densities were comparable to those in less-disturbed streams. The study revealed that BMCs in mining-influenced streams were less diverse and were likely functioning less effectively than BMCs in forested reference streams. Also, the measurement and analysis methods used to characterize BMC structural responses to pollution influence assessments of stream condition. Understanding the responses of benthic macroinvertebrate structure to changes in habitat and water quality in mining-influenced streams can inform future stream management efforts.

Following the construction of the Pongolapoort Dam in 1974, the potential impacts on the lower Phongolo River and floodplain due to alterations in the natural flow regime have caused concerns. Fish communities and population structures are directly influenced by these alterations. The only protected section of the Phongolo River is a 15 km reach and its associated pans that flow through the Ndumo Game Reserve. Historic data shows that the community and population structure of the fish in the Phongolo Floodplain has changed as a result of irregular flood releases. The Ndumo Game Reserve plays an important role in the conservation of many ecologically and economically important species as the pans inside the reserve serve as a refuge area in which these species can breed to replenish the fish numbers in the Phongolo River. The fish diversity inside the Ndumo Game Reserve is also higher when compared to outside. During the high flow period fish move into the floodplain pans as a result of the higher water level. Oreochromis mossambicus, the most common species found in this area, utilize Nyamiti Pan for breeding but the health of this species is under pressure due to severe infestations of Lernaea cyprinacaea and nematode parasites. Lernaea cyprinacaea is a parasitic copepod associated with the introduced exotic fish species Cyprinus carpio which is found in large numbers in various pans inside Ndumo Game Reserve. The presence of this alien species in the refuge area raises concerns as it competes for the same resources as the economically important native fish species. Nyamiti Pan is largely populated by adult cichlid species between the ages of six and ten years old. The importance of flood releases which simulate natural flow regime is emphasised by the negative impacts irregular floods have on fish health, community and population structure. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Following the construction of the Pongolapoort Dam in 1974, the potential impacts on the lower Phongolo River and floodplain due to alterations in the natural flow regime have caused concerns. Fish communities and population structures are directly influenced by these alterations. The only protected section of the Phongolo River is a 15 km reach and its associated pans that flow through the Ndumo Game Reserve. Historic data shows that the community and population structure of the fish in the Phongolo Floodplain has changed as a result of irregular flood releases. The Ndumo Game Reserve plays an important role in the conservation of many ecologically and economically important species as the pans inside the reserve serve as a refuge area in which these species can breed to replenish the fish numbers in the Phongolo River. The fish diversity inside the Ndumo Game Reserve is also higher when compared to outside. During the high flow period fish move into the floodplain pans as a result of the higher water level. Oreochromis mossambicus, the most common species found in this area, utilize Nyamiti Pan for breeding but the health of this species is under pressure due to severe infestations of Lernaea cyprinacaea and nematode parasites. Lernaea cyprinacaea is a parasitic copepod associated with the introduced exotic fish species Cyprinus carpio which is found in large numbers in various pans inside Ndumo Game Reserve. The presence of this alien species in the refuge area raises concerns as it competes for the same resources as the economically important native fish species. Nyamiti Pan is largely populated by adult cichlid species between the ages of six and ten years old. The importance of flood releases which simulate natural flow regime is emphasised by the negative impacts irregular floods have on fish health, community and population structure. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Platinum mining activities contribute substantially to South Africa's economy since it exceeded gold as economical contributor in 2001. Mining activities contribute to large amounts of waste production in the form of tailings and rock waste, deposited in the surrounding environment of the mine premises. Mining companies are held responsible for damages caused to the surrounding environment. These companies are required to introduce the cost of ecological rehabilitation in their operation costs as well as compile an environmental management plan. Numerous attempts to rehabilitate mine waste have proven unsuccessful. New and improved rehabilitation techniques are required to facilitate in the rehabilitation of these mine spoils. Woodchip-vermicompost produced from platinum mining wastes (woodchips and sewage sludge) was used as an alternative amendment to inorganic fertilisers during the rehabilitation of platinum mine tailings. The effectiveness of the woodchip-vermicompost as an alternative amendment during the platinum mine tailings rehabilitation were monitored using different ecosystem components. A natural veldt in the vicinity of the mine area was randomly selected to serve as a reference site. These ecosystem components selected have previously been shown to be effective as indicators of ecosystem quality. The components selected for this study includes the use of microbial enzymatic activity, microbial community structure, nematode trophic structures, and other mesofaunal groups such as micro-arthropods. The physical and chemical properties of the platinum mine tailings and reference area as well as the vegetation cover of the platinum mine tailings were determined. Statistical and multivariate analyses were use to determine the correlation between the dependent microbial components and dominate independent chemical properties. Nematode trophic structure, Maturity Index, and Plant-Parasitic nematode Index were used to compare the two rehabilitation techniques in terms of nematodes as indicators. Microarthropods family structures were used to compare the two amendments in terms of diversity and abundance. Enzymatic activity was positively affected by the addition of woodchip-vermicompost, than in the sites treated with inorganic fertilisers. The microbial community structure showed no statistically significant (p < 0.05) differences between the two amendments. A higher abundance of nematodes especially plant-parasitic nematodes and bacterivorous nematodes were observed in the woodchip-vermicompost sites than in the inorganic fertilised sites. According to the Maturity Index, both amendments became more enriched during the study period, while the Plant-Parasitic nematode Index showed that the carrying capacity for plantparasitic nematodes on the woodchip-vermicompost sites increased while it decreased in the inorganic fertilised sites, which can be related to the decrease in vegetation cover on the inorganic fertilised sites. Both coloniser (Prostigmata) and persister (Cryptostigmata and Mesostigmata) groups of the micro-arthropods, as well as a higher diversity of micro-arthropods, were present on the woodchip-vermicompost sites whereas the inorganic fertilised sites showed only the presence of colonisers, with a decrease in diversity and abundance of micro-arthropods over the study. The colonisation of micro-arthropods may have been affected by the addition of woodchip-vermicompost and vegetation cover, which contribute to the establishment of suitable microhabitats for these soil biota. By intercorrelating the results, it may be concluded that the addition of woodchip-vermicompost may be an essential part of the rehabilitation process, by contributing to soil organic material to the ecosystem system, which may improve the recolonisation of soil biota and ecosystem processes. However further studies need to be conducted in order to determine the long-term sustainability of the woodchip-vermicompost in providing organic material and sustaining the ecosystem processes. The study also showed the necessity to integrate various ecosystem components when evaluating ecosystem development due to the unique role each component plays and the impact it may have on other components. / Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2006.

Substrate specificity of epiphytic communities of diatoms (Bacillariophyceae) and desmids (Desmidiales) Bc. Petra Mutinová Master's thesis, Prague, 2015 Abstract It has been always assumed, and frequently reported, that host plants, as biologically active substrates, should have a direct influence on associated epiphyton. However, some studies favoured the neutral substrate hypothesis. Thus the relationship between host plant and epiphytic community remained unresolved. This Master's thesis focused on the basal question that numerous previous studies overlooked. Is there any significant influence of host plant on freshwater algal epiphyton in comparison to the influence of other factors, e.g. site and environmental conditions? In addition, substrate specificity of individual algal taxa was investigated. The research concerned several types of natural plant substrates at several water bodies in the Czech Republic, which provided a more accurate and general insight in the ecology of microphytobenthos. The results have demonstrated that site was the main factor affecting epiphytic community structure, followed by mild, but still noticeable, effect of environmental conditions (pH and conductivity). In contrary, host plant had almost no influence and very few algal species were found to be host specific....

Master of Science / Department of Statistics / Leigh Murray / The southern root-knot nematode (SRKN) and the weedy perennials, yellow nutsedge (YNS) and purple nutsedge (PNS) are simultaneously occurring pests in the irrigated agricultural soils of southern New Mexico. Previous research has very well characterized SRKN, YNS and PNS as a mutually-beneficial pest complex and has revealed their enhanced population growth and survival when they occur together. The density of nutsedge in a field could be used as a predictor of SRKN juveniles in the soil. In addition to SRKN, which is the most harmful of the plant parasitic nematodes, in southern New Mexico, other species or categories of nematodes could be identified and counted. Some of them are not as damaging to the plant as SRKN, and some of them may be essential for soil health. The nematode species could be grouped into categories according to trophic level (what nematodes eat) and herbivore feeding behavior (how herbivore nematodes eat). Subsequently, three ratios of counts were calculated for trophic level and for feeding behavior level to investigate the soil nematode community structure. These proportions were modeled as functions of the weed hosts YNS and PNS by generalized linear regression models using the logit link function and three probability distributions: the Binomial, Zero Inflated Binomial (ZIB) and Binomial Hurdle (BH). The latter two were used to account for potential high proportions of zeros in the data. The SAS NLMIXED procedure was used to fit models for each of the six sampling dates (May, July and September) over the two years of the alfalfa study. General results showed that the Binomial pmf generally provided the best fit, indicating lower zero-inflation than expected. Importance of YNS and PNS predictors varied over time and the different ratios. Specific results illustrate the differences in estimated probabilities between Binomial, ZIB and BH distributions as YNS counts increase for two selected ratios.

In protists a biodiversity hotspot could be defined as region with exceptionally high ratio of local to global species diversity. In 2012 Aquitaine (France) was revealed to represent a hotspot of Synurales (lineage within silica-scaled chrysophytes). To investigate how the diversity is distributed and where the species are hidden, samples from 42 lakes were collected during spring peak of Chrysophyte occurrence (from March 27th to March 31st ). Samples were taken in two microbiotopes - phytoplankton and metaphyton. Metaphyton was represented by different substrates (aquatic plants). I identified seventy-six species from genera Mallomonas and Synura, which confirmed Aquitaine to be a hotspot. In this thesis, I investigated ecological drivers of chrysophytes diversity and community structure. The chrysophyte diversity was driven mostly by mutual impact of pH and conductivity, north-south gradient of lakes location and sampled microbiotopes. Number of identified species increased with increasing pH and conductivity, with increasing size of waterbody and with location of the lake more towards the South. More taxa were revealed from metaphyton (77) than from plankton (61), substrates played an important role. Lakes in Aquitaine are rich in different species of aquatic plant, which immersed create...

Esta pesquisa foi desenvolvida nas lagoas facultativas das estações de tratamento de esgoto dos municípios de Pariquera-Açu (PA) e Jacupiranga (JA), com diferentes configurações, sendo a primeira composta por lagoa anaeróbia seguida de facultativa com chicanas e a outra por lagoa aerada mecanicamente seguida de facultativa. Estas lagoas são consideradas ambientes hipereutróficos, pois apresentam grande quantidade de matéria orgânica oriunda dos esgotos domésticos e industriais. O conhecimento da estrutura da comunidade fitoplanctônica e sua avaliação em diferentes horários do fotoperíodo são relevantes pois estes organismos são responsáveis pela produção de oxigênio necessário para a degradação da matéria orgânica. Esta pesquisa teve como objetivo principal o estudo sazonal e diário da estrutura da comunidade fitoplanctônica e da produção primária nestas lagoas. Para atingir este objetivo foi caracterizada a estrutura da comunidade, em relação a biomassa e diversidade, e determinada a produção primária com incubações in situ através do método do oxigênio dissolvido. O estudo foi realizado em quatro épocas do ano (variação sazonal) no período das 7 às 16 horas, com amostragens de 3 em 3 horas (diária). Não foram observadas variações temporais e espaciais na estrutura da comunidade fitoplanctônica nas duas lagoas facultativas. Apenas as cianobactérias (principalmente a Synechocystis aquatilis e Phormidium sp) e clorofíceas (Kirchneriella lunaris, Chlorella Kessleri, Monoraphidium contortum, Monoraphidium sp, Chlamydomonas sp, Eutetramorus planctonicus e Micractinium pusillum) foram predominantes, nestas lagoas, porém em períodos alternados. Foram observados altos valores de produção primária bruta (15.891 mg\'O IND.2\'/\'M POT.3\'.h em PA; 5.700 mg\'O IND.2\'/\'M POT.3\'.h em JA) na interface água-sedimento das duas lagoas devido, provavelmente, ao padrão de mistura da coluna de água. Foram também observados altos valores de respiração da comunidade (abril, julho e setembro), devido à alta concentração de matéria orgânica presente nestes sistemas e, portanto, maior decomposição, indicando predominância de processos heterotróficos. / This research was developed in facultative ponds of the waste water treatment plant of Pariquera-Açu and Jacupiranga cities with different configurations, being the first composed by anaerobic pond followed by facultative with chicanas and the another composed by aerated mechanic pond followed by facultative. These ponds are considered hypereutrophic environments because it shows a large quantity of organic matter derived from the domestic and industrial sewage. The knowledge of phytoplanktonic community structure and its evaluation in different times of photoperiod are relevant since such organisms was responsible by production of oxygen necessary to the degrade of organic matter. This research had the main goal the seasonal and daily study of the phytoplanktonic community and the primary production in these ponds. To reach this objective the structure of the community was characterized in relation to biomass and density, and determined the primary production with incubations in situ through the dissolved oxygen method. The study was made in four periods of the year (seasonal variation) between the 7 a.m. to 4 p.m., with samplings of 3-to-3 hours (daily). It was not observed temporal and spatial variations in the phytoplanktonic community structure in the facultative ponds. Only cyanobacteria (mainly Synechocystis aquatilis and Phormidium sp) and chlorophycea (Kirchneriella lunaris, Chlorella Kessleri, Monoraphidium contortum, Monoraphidium sp, Chlamydomonas sp, Eutetramorus planctonicus and Micractinium pusillum) were predominant in these ponds, however, in alternated periods. It was observed high rates of gross primary production (15891 mg\'O IND.2\'/\'M POT.3\'.h, PA; 5700 mg\'O IND.2\'/\'M POT.3\'.h, JA) in the interface water-sediment of both ponds due, probably, to the standard of mixed conditions of water column. It was also observed high rates of community respiration (April, July and September), due to the high concentration of organic matter present in these systems and, therefore, greater decomposition, indicating predominance of heterotrophic processes.

Este trabalho teve como objetivo investigar a recuperação da fauna durante a sucessão florestal, através de duas abordagens distintas. No primeiro capítulo, visando a identificação das lacunas e oportunidades para o avanço do tema, realizamos uma revisão de artigos sobre sucessão em comunidades animais em florestas neotropicais analisados criticamente quanto: (1) às regiões e grupos estudados, (2) à qualidade dos trabalhos com relação a adequação do delineamento amostral, (3) aos padrões observados (diversidade, biomassa e estrutura), e (4) à base teórica utilizada. Foram encontrados e analisados 33 trabalhos, os quais focaram em poucos grupos da fauna, principalmente aves, mamíferos e formigas. No geral, a maioria dos trabalhos é descritiva, não explicitando expectativas sobre os padrões e mecanismos responsáveis pela recuperação da fauna, não apresenta delineamento amostral adequado, principalmente no que se refere à justificativa da alocação dos sítios de amostragem com relação a fatores de confusão, e quantifica de maneira categórica, e muitas vezes imprecisa e arbitrária, a sucessão. As lacunas identificadas nesta revisão apontam a limitação do conhecimento atual sobre os padrões e mecanismos associados à sucessão em comunidades animais em florestas neotropicais, o que conseqüentemente implica na falta de informações que embasem a elaboração de planos de manejo e restauração destas florestas. Já o segundo capítulo refere-se à investigação empírica da recuperação da comunidade de pequenos mamíferos entre estádios sucessionais em uma área contínua de Mata Atlântica. Verificamos a congruência das modificações observadas na riqueza, composição e estrutura da comunidade estudada com as expectativas geradas pelos dois principais mecanismos propostos na literatura: (1) substituição de espécies causada por demandas conflitantes (trade-offs), associada ao gradiente de produtividade primária líquida e disponibilidade de recursos durante a sucessão, ou (2) aumento de diversidade causado pela possibilidade de partição de nicho, associado ao aumento da biomassa e da complexidade da vegetação, e da diversidade de recursos durante este processo. Embora a riqueza, estrutura e composição da comunidade não tenham sido influenciadas pela sucessão, houve uma mudança na abundância de parte das espécies da comunidade, com algumas aumentando e outras diminuindo das matas mais jovens para as mais tardias. Nossos resultados indicam que a hipótese de demandas conflitantes é mais plausível para explicar a recuperação da fauna de pequenos mamíferos durante a sucessão florestal / This study aims at investigating fauna recovery during forest succession using two distinct approaches. In the first chapter, in order to identify the gaps and opportunities for advancing our understanding of this subject, we carried out a review of articles on succession in animal communities in neotropical forests, which were critically analyzed in relation to: (1) the study regions and study groups, (2) the quality with respect to the adequacy of the sampling design, (3) the observed patterns (diversity, biomass and structure), and (4) the theoretical basis. We found and analyzed 33 studies, which focused on a few wildlife groups, especially birds, mammals, and ants. In general, most studies are descriptive, with no explicit expectations about the patterns and mechanisms responsible for wildlife recovery, lack adequate sampling design, especially concerning the justification for the allocation of sampling sites with respect to confounding factors, and quantify succession into categories, which are often imprecise and arbitrary. The gaps identified in this review indicate the limitation of our current knowledge on the patterns and mechanisms associated with succession in animal communities in neotropical forests, which consequently implies in the lack of information for developing management and restoration plans for these forests. The second chapter refers to an empirical investigation on the recovery of small mammal communities across successional stages in a continuous area of Atlantic Forest. We verified the congruence of the observed changes in community richness, composition and structure with the expectations generated by the two main mechanisms proposed in the literature: (1) species replacement caused by trade-offs, associated with the gradient in net primary productivity and resource availability during succession, or (2) increase in diversity caused by the possibility of niche partitioning, associated with increased vegetation biomass and complexity, and increased resource diversity during this process. Although community richness, structure and composition were not influenced by succession, there was a change in the abundance of some species, with some increasing and others decreasing from younger to older forests. Our results indicate that the hypothesis on trade-offs is more plausible to explain the recovery of small mammal communities during forest succession

Les essences de forêts tropicales sont caractérisées par une importante variabilité de la qualité et de la stœchiométrie des feuilles qui tombent au sol. Les microorganismes hétérotrophes à la base des réseaux trophiques de décomposeurs dépendent principalement de ces ressources organiques qui varient de façon substantielle à petite échelle quant à la quantité et la contribution relative de certains éléments clés tels que le carbone (C), l'azote (N) et le phosphore (P). J'ai évalué au cours de cette thèse comment les variations de qualité et de stœchiométrie C:N:P de la ressource influençaient l'activité, la biomasse, la stœchiométrie et la structure des communautés des décomposeurs microbiens. J'ai réalisé ce travail en forêt Amazonienne de Guyane française sur des sols extrêmement appauvris en nutriments où les microorganismes hétérotrophes sont supposés être particulièrement dépendants du C et des nutriments provenant des litières. J'ai d'abord démontré que la qualité du C et le contenu en P des feuilles de litières expliquaient plus de 50% de la variabilité observée du processus de respiration microbien (SIR) du sol sous-jacent. Lors d'une expérience de fertilisation factorielle avec du C (sous forme de cellulose), de l'N (sous forme d'urée) et du P (sous forme de phosphate) sur le terrain, j'ai ensuite confirmé que la SIR de la communauté du sol était co-limitée par C et P, alors la SIR dans la litière était co-limitée par N et P. Ces limitations différentielles dans les litières et le sol sous-jacent étaient reliées à des modifications de la structure des communautés microbiennes, et en particulier des changements du ratio champignon:bactérie et de la proportion de bactéries copiotrophes et oligotrophes. Finalement au cours d'une expérience d'incubation au laboratoire, j'ai montré que la biomasse, la stœchiométrie et la structure des communautés microbiennes de la litière différaient fortement entre six litières chimiquement contrastées variant dans leur stœchiométrie initiale C:N:P. Cependant, les variations des paramètres microbiens étaient mieux expliqués par les caractéristiques de la fraction soluble des litières (y compris sa stœchiométrie) que par la qualité de la litière dans son ensemble, entrainant des variations de la stœchiométrie de la biomasse microbienne et un shift vers une dominance fongique en réponse à une augmentation de la stœchiométrie C:N:P des lessivâts. Collectivement, ces résultats montrent que des qualités de litière distinctes produites par une importante diversité d'essences forestières contrôlent la structure, la stœchiométrie, l'abondance et l'activité des communautés microbiennes des litières à petites échelles spatiales en forêt tropicale d'Amazonie. Par ailleurs, les litières en décomposition stimulent également les communautés microbiennes du sol sous-jacent, qui apparaissent être limitées par l'accès combiné à une source de C (énergie) et de P. L'importance de la contrainte stœchiométrique pour les microorganismes hétérotrophes à la base des réseaux trophiques de décomposeurs suggère que des modifications de la composition des communautés végétales ou des dépositions atmosphériques de N et/ou P peuvent avoir des conséquences plus lointaines sur les cycles du C et des nutriments au sein des biomes tropicaux. / Tree species-rich tropical rainforests are characterized by a high variability in quality and stoichiometry of leaf litter input to the soil. Microbial heterotrophs in the decomposer food web depend primarily on these organic resources that can vary dramatically in quantity, quality and relative contribution in key elements such as carbon (C), nitrogen (N), and phosphorus (P). I evaluated during this thesis how differences in leaf litter resource quality and C:N:P stoichiometry influence the activity, biomass, stoichiometry and community structure of microbial decomposers. I did this work in the Amazonian rainforest of French Guiana, where the soils are highly nutrient-impoverished and microbial heterotrophs are assumed to be particularly dependent on litter-derived nutrients. I first showed that leaf litter C quality and P content explained more than 50% of the observed variability of the microbial respiration process in the underlying soil. Using a fertilization experiment with C (as cellulose), N (as urea), and P (as phosphate) in the field, I further showed that microbial respiration process in the litter layer was co-limited by N and P, while that in the soil was co-limited by C and P. Additionally, distinct nutritional limitations in litter and underlying soil were related to shifts in the microbial community structure, especially regarding the fungi:bacteria ratio and the proportion of copiotrophic versus oligotrophic bacteria. Finally, during a laboratory incubation experiment, I showed that litter microbial biomass, stoichiometry and community structure differed strongly among leaf litter from six different tree species varying in C:N:P stoichiometry. The variations in microbial parameters among substrate litters, however, were not related to bulk leaf litter quality, but rather driven by the stoichiometry of the soluble fraction, with larger microbial C:nutrients ratios and a shift towards fungal dominance with increasing litter leachate C:N:P stoichiometry. Collectively, these results showed that the distinct leaf litter quality produced by a diverse tree canopy controls the structure, stoichiometry, abundance and activity of microbial communities in the studied Amazonian rainforest at small spatial scales. Moreover, the decomposing leaf litter stimulates microbial communities in the underlying soil that appear to be under the combined control of energy (C) and P availability. The strong stoichiometric constraint on microbial heterotrophs in the decomposer food web suggests far-ranging consequences on ecosystem C and nutrient cycling with ongoing alteration of nutrient deposition and tree species diversity in tropical rainforests..