Processo de decomposição da serrapilheira atuando como mecanismo de facilitação

Abstract

Facilitation is a interaction in which one plant species (nurse) has a positive effect on the development and survival of other plant species (target) by increasing resource availability or providing better abiotic conditions. Nurse tree species might facilitate other plants growing under their canopy by providing nutrient supply below and around their crown. Leaf litter decomposition, is the major nutrient transfer pathway from vegetation to soil. Thus, leaf quality, leaf biomass production and leaf decomposition rates can influence soil fertility and consequently plant productivity below nurse canopies. However, external sources such as animals, atmospheric dust and leaching also contribute to soil fertility. Although the studies that investigate plant facilitation through nutrient availability below tree canopies acknowledge the role of leaf litter decomposition, they do not assess how facilitation might act directly on litter decomposition. Leaf decomposition depends on biotic and abiotic factors, and leaf nutritional quality is one of the most determinant for defining the speed of decomposition. However, several studies report the effects of diversity and species richness on leaf litter decomposition. In forest ecosystems with high diversity, leaves of several trees form a mixed leaf litter layer. Therefore it is also necessary to assess the effects of leaf species richness on decomposition rates. The present study aims to investigate whether nutrient transfer from tree species to soil by leaf decomposition is able to influence facilitation and inhibition interactions between plant species. Fourteen typical and abundant Caatinga species were classified as facilitators, neutral or inhibiters, according to their interspecific interaction index “INE” (Fagundes et. al., 2016). Leaf fall rates, leaf nutritional content (C and N) and leaf decomposition rates of each species were measured. The product of these three measurements was considered as the nitrogen transfer potential from tree to the soil for each species (PTN). The results indicated that nurse species have a greater nutrient transfer potential than inhibitory species, indicating that "PTN" may be one of the factors that influence facilitation interactions between plants. A leaf mixed litter experiment using nurse or inhibiting species was also carried out to assess richness effects on decomposition. Leaves were mixed at 04 different richness levels (2, 4, 7 and 14), forming 15 different compositions. The species compositions containing nurse species showed a positive effect on decomposition rates, while species compositions containing inhibitory species had a negative effect. There was no significant effect of increasing species richness on leaf litter decomposition processes. These results indicate that leaf mixture effects on litter decomposition rates depend on the species present in the compositions and not on richness. From the results obtained in this study it is concluded that leaf litter decomposition might play an important role on the Facilitation process.