Através do Tempo: avaliando o padrão de decomposição foliar em um riacho de Mata Atlântica.

Abstract

Organic matter decomposition is a fundamental ecological process for carbon and nutrient cycling in headwater streams, especially in tropical ecosystems where allochthonous leaf litter is the primary energy source sustaining the aquatic food web. However, understanding the dynamics of this process at broader temporal scales, particularly in tropical regions characterized by high environmental and biological heterogeneity, remains limited due to the scarcity of long-term data. This study investigated the influence of temporal variation and multiple environmental factors on the decomposer community and the process of organic matter decomposition in a headwater stream of the Brazilian Atlantic Forest over five years. The research was structured into two main chapters. Chapter 1 evaluated the structure of aquatic hyphomycete fungal communities, whose main ecological role is leaf conditioning and nutrient mineralization during decomposition. The results revealed that interannual variation had a stronger influence on hyphomycete community structure than intra-annual variation. The main environmental drivers shaping this community were water chemistry and leaf litter quality. This pattern contrasts with the initial hypothesis, which predicted a stronger influence of intra-annual variation, and instead indicates notable seasonal stability and the predominance of long-term environmental shifts. Chapter 2 investigated the direct and indirect relationships between temporal and environmental factors, the structure of the decomposer community, and organic matter decomposition using Structural Equation Modeling (SEM). The model showed that timescale and the composition of dissolved nutrients in the water were the main drivers of decomposer community structure. Interestingly, decomposition was not directly explained by any of the variables included in the model, suggesting the presence of functional redundancy and ecological resilience in the decomposition process. In conclusion, this thesis advances our understanding of how temporal variability and the complex interactions among environmental and biological factors shape decomposition in tropical streams. The findings highlight the importance of long-term approaches for uncovering ecological processes in dynamic ecosystems and provide valuable insights for the conservation and management of headwater stream integrity under climate change pressures.