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In this study, we have shown that nutrient input in aquatic ecosystems has different impacts on the various facets of phytoplankton and zooplankton diversity. We designed an experiment with eleven levels of nutrient addition replicated four times. Alpha, beta, and gamma taxonomic and functional diversity indices were calculated based on organisms' occurrences and abundances in each microcosm, among microcosms of the same treatment and for the set microcosms of a same treatment. There was an increase in species richness and a decrease in equitability along the gradient for both groups. Taxonomic beta diversity based on occurrences was positively related to nutrient gradient, but a hump-shaped relationship between nutrient enrichment and beta diversity was observed when abundance data were considered, showing greater variation in species composition at intermediate levels of nutrient. Alpha functional richness increased for both groups, whereas alpha and gamma RaoQ, and gamma functional divergence decreased, indicating that nutrient enrichment promotes functional trait richness, but also the dominance of species. At small spatial scale and at a short period of time, we showed that taxonomic and functional diversities respond in similar ways to nutrient enrichment. We conclude that nutrient input may modify community composition and affect ecological processes overtime. [ABSTRACT FROM AUTHOR]

We determined the variation in the composition of plankton communities (zooplankton, phytoplankton, and ciliates) in subtropical lakes at different temporal scales, in relation to the seasons (dry and rainy seasons), as well as at finer (among months) and broader (ENSO—among El Niño, La Niña, and normal climate events) scales. Using a 16-year time-series dataset, we tested the hypothesis that seasonal variation would explain most of the gamma diversity of these plankton communities. We also investigated the environmental and temporal factors responsible for the variations in composition and species turnover. The scale related to dry and rainy seasons explained a considerable percentage of the gamma diversity and variation partitioning, showed that compositional changes occurred mainly over broader temporal scales. Environmental factors varying among seasons and ENSO events explained changes in composition, although some communities did not respond to the environment. Our results suggest that niche and stochastic processes operating at temporal scales correlated with ENSO climate events contributed to changes in species composition. Hence, climate anomalies might be important to maintain diversity in areas with reduced or loss of the natural variations in environmental conditions. Our results also suggest that, although communities show similar patterns of variation in composition, they might respond in a different degree to environmental and temporal factors. Thus, while niche-associated (environment) and stochastic (time) processes drove the phytoplankton, stochastic processes were more important for zooplankton, whereas neither were important for ciliates. [ABSTRACT FROM AUTHOR]