Fatores controladores da fenologia da queda de serrapilheira e seus impactos na multifuncionalidade do ecossistema numa floresta tropical semidecídua

Abstract

Aspects of plant phenology, such as the contribution of litter from different plant organs to the soil, may be modulated by biotic, such as species composition and diversity, and abiotic factors, such as climate related ones. The relative importance of these factors on the plant phenology litter input generally depends on the intensity of the environmental filters. In this study, we tested the importance of biotic and abiotic factors on the phenology of the litterfall and its consequences for the functioning of a semi-deciduous tropical forest, known as Restinga. In chapter 1, we tested whether and how the seasonality of the phenology of the leaf, branches and reproductive material input, described their phenologies and whether such phenologies respond differently to different controlling factors. The litter contribution from all plant organs showed a seasonal behavior, and reproductive phenology was the most seasonal. The phenology of leaf litter input was correlated negatively to precipitation and relative humidity, and positively to insolation. The phenology of reproductive material was negatively related to the relative humidity of the air, while the phenology of the supply of branches was positively related to the wind speed. Given its important contribution in terms of matter and energy to the forest ecosystem, we seek to understand the relative importance of the diversity of vegetation for the seasonality of the phenology of leaf litter input compared to other environmental determinants (Chapter 2). We hypothesized that assemblies with greater wealth would be less seasonal, due to the greater adaptive complementarity of leaf loss in response to water stress (i.e. temporal occurrence). Through a path analysis, we found that species richness negatively affects seasonality and temporal overlap, but that temporal overlap has no effect on the seasonality of leaf-fall. In addition, the availability of potassium (K) in the soil had a positive effect on seasonality. The results indicate that the dominance in the vegetation, possibly mediated by the availability of K in the soil, determines the phenological pattern of the contribution of leaf detritus in the plant assemblages richer in species. In chapter 3, we seek to understand the role of different dimensions of biodiversity (taxonomic, functional and phylogenetic) and several abiotic factors on ecosystem multifunctionality, determined here as the integrality of quantitative characteristics (ie mass of C, N, P, K, Ca , Na, Mg) and qualitative (ie C: N, C: P and N: P ratio of debris input.) We observed that multifunctionality was mainly determined by abiotic factors, such as precipitation (negatively), the slope of the terrain and to the content of K in the soil.