Interações espécie-habitat na decomposição da serrapilheira: efeitos moduladores da diversidade de detritos e heterogeneidade ambiental

Abstract

Litter decomposition is a key ecological process for nutrient cycling, regulated by complex interactions between biotic factors (e.g., litter quality and decomposer abundance/diversity) and abiotic factors (e.g., temperature, moisture, and solar radiation), yet their context-dependent modulation remains poorly understood. Here, we investigated how spatial heterogeneity, seasonality (temporal variation between dry/wet periods), and litter quality/functional diversity drive decomposition dynamics in habitats with distinct environmental drivers. Using litterbag experiments, we assessed: (1) functional traits predicting decomposition in abiotic Vs. biotic-driven habitats; (2) context-dependent nonadditive resident of litter mixtures effects on the keystone species Encholirium spectabile ("macambira-de-flecha"); and (3) interactive effects of habitat and litter diversity. In chapter 1, we identified the chemical and physical functional traits that best predict decomposition in habitats that modulate decomposition by biotic vs. abiotic factors, as well as the traits that best predict the relative difference in decomposition rates of different species between these habitats. We observed that, in habitats where biotic factors predominate over decomposition (habitats shaded by dense canopies), decomposition was associated with traits related to palatability for decomposers. In habitats under strong influence of abiotic factors (habitats exposed to the sun and without vegetation), in addition to chemical traits, physical functional traits were critical for litter decomposition. However, contrary to what we expected, the traits that best explained the difference between decomposition in habitats are not linked only to the habitat that most influenced litter decomposition. In chapter 2, we evaluated how the decomposition of the key habitat-forming species Encholirium spectabile (Macambira-de-flecha)) is affected by the litter of tenant species in three habitat conditions associated with E. spectabile clumps: inside, on the edge of, and outside the macambira clumps, under seasonal variation in sequences of dry and rainy regimes. The results indicated that within the clumps (microclimate with lower temperatures and less variability in abiotic conditions), mixtures with leaves of inquines-species accelerated the decomposition of E. spectabile in the seasonal sequence in which the litter begins and ends to decompose during the dry season. This possibly occurred because the mixture provided greater complementarity to the litter of the habitat-forming species, as the habitat provided better conditions for the establishment of decomposers during dry periods. At the edge of the clumps (with intermediate temperature and light variation), the decomposition of E. spectabile also accelerated in the same seasonal sequence, indicating complementarity between biotic decomposition and photodegradation. Outside the clumps (high temperature variation and constant light), the decomposition of the leaf litter of the macambira-de-flecha slowed down in the presence of the leaf litter of the inquiline species, both in the seasonal sequence in which the detritus begins and ends to decompose in the dry season and in the rainy season. This is due to a possible interference of the release of compounds that inhibit the decomposers, as well as to shading that hindered the photodegradation process. Finally, in chapter 3 we tested how the effects of detritus diversity are modulated by habitat diversity. Contrary to our hypotheses, our results demonstrated that at the assemblage level (i.e., total decomposition of all species in a mixture), positive effects of decomposition on decomposition occurred when the detritus decomposed in a single habitat where similar environmental factors prevailed and negative effects occurred when the litter decomposed in different habitats where the greatest diversity (variability) of environmental factors occurred. Thus, showing that habitat diversity generated effects that may have nullified or diminished patterns of complementarity of the litter mixture. On the other hand, at the species-specific level the interaction between habitat and litter diversity varied depending on the litter quality. Species with higher SLA (Specific Leaf Area) tended to have antagonistic effects, compared to species with lower SLA in more diverse habitats. These results reveal possible mechanisms dependent on habitat diversity, in addition to those described by litter diversity alone. In summary, the results of this thesis show that the effects of litter mixing and the influence of specific functional attributes are strongly conditioned by context-dependence mechanisms in microhabitats, which are modulated by complex interactions between litter diversity, habitat structural heterogeneity and local environmental gradients. These findings highlight not only the multifactorial nature of decomposition, but also reinforce the need to incorporate multiple spatial (including microhabitats), temporal (seasonal variations) and functional (functional attributes and species interactions) scales of analysis into predictive models capable of capturing the dynamics of the decomposition process.