Funções ecossistêmicas de florestas ripárias: análise das taxas de decomposição foliar em um gradiente de fertilidade de solo

Abstract

A potential indicator in the monitoring of restored areas is the decomposition of the organic matter, an important ecosystem function responsible for nutrient cycling, which may vary in relation to soil nutrients availability and vegetation structure. For this reason, this study evaluated the process of organic matter decomposition among three vegetation types: 1) restored riparian forest, 2) pasture and 3) a riparian forest remnant, all of them located along a gradient of soil nutrients. Therefore, it was possible to evaluate both direct and indirect effects of nutrients and vegetation structure on the decomposition process, which was evaluated using the Tea Bag Index (TBI) method. Data were analyzed with a structural equations model, which showed that the decomposition rates were influenced jointly by differences in soil chemical composition and vegetation structure. The vegetation structure had a negative effect on the rate of decomposition by restricting the entry of light into the soil, and consequently, reducing the activity of the decomposing community. Differently, soil chemical composition showed both direct and indirect positive effects (through vegetation structure) in the decomposition, with higher microbial activity possibly due to higher nutrient availability. Therefore, to evaluate the decomposition process in this system it is necessary the evaluation of both soil chemical composition and vegetation structure to separate the contribution of each effect. Ecosystem processes can respond both to differences in soil properties and to the recovery of the vegetation, therefore the monitoring the recovery of ecosystems in riparian forests should include both types of variables.