Ciclagem de nutrientes em fragmento de floresta ombrófila densa das terras baixas, na Zona da Mata de Pernambuco

Abstract

The Atlantic Forest, considered the second largest rainforest on the American continent, exert an important role in ecological balance, although the anthropic actions cause a loss and fragmentation of this biome. As a result of these high anthropic actions, litter and outflow from the trunk accrue from rainfall, have become essential sources of nutrients for the ecosystem. In view of the lack of information on this theme, this work aimed to evaluate the dynamics of nutrient cycling through leaf biomass, litter supply and runoff through the trunk in a fragment of Dense Ombrophilic Forest of the Lowlands, in the Zona da Mata of Pernambuco. Data collection was carried out in a forest fragment located in Sirinhaém, Pernambuco. Based on a phytosociological survey carried out in the area, the nine species with the highest absolute density in the fragment were determined. Three individuals of each species were selected and 25 leaves were collected from the middle part of the crown at the four cardinal points of each individual. The leaf biomass of each species was determined using allometric equations and the levels of micronutrients in the leaves were determined. Finally, the micronutrient stock and the biological utilization efficiency of forest species were calculated. The collection of litter was realized monthly for a year in three different periods, being them: wet and cold; hot and dry; and, wet and hot. In the litter produced, the levels were determined and the micronutrient contributions were calculated. This, it was possible to estimate the decomposition rate and average renewal time of this litter. Runoff through the trunk was quantified monthly, in the rainy season, subdivided into two periods: less rainy and more rainy using collectors fixed around the trunk arboreal individuals of the species with the highest absolute density. The total and internal precipitation was measured using rain gauges installed inside and at the edge of the fragment. The water flowing through the trunk was measured in milliliters, an aliquot was taken, the pH and electrical conductivity were measured and the K, P and Na input was determined. Through total precipitation, effective precipitation and runoff, effective precipitation was calculated. Forest species used micronutrients differently, favoring interspecific interactions and with the site that are included. The forest species used the micronutrients differently, favoring the interspecific and site interactions that are included. The climatic variations interfered in the litter supply, in the dry and hot period there was a greater deposition. The decomposition rate for the wet periods was around 90%, indicating that during these periods there is rapid decomposition and, consequently, the availability of the nutrients contained in the litter for the ecosystem. Runoff through the trunk of forest species differed by species and had little influence from the rainy season, and proved to be an important pathway for nutrients to enter forest ecosystems, mainly K, effectively participating in nutrient cycling