Deposição,composição química e decomposição de liteira em um bosque de sabiá (Mimosa caesalpiniifolia Benth) , Itambé-PE

Abstract

The objective of this experiment was to evaluate the deposition, chemical composition, and decomposition of litter in a sabiá (Mimosa caesalpiniifolia Benth) canopy. The experiment was carried out at the Experimental Station of Itambé-IPA. The evaluation of existing and deposited litter was carried through the period of August of 2006 until July of 2007, every 28 days. Twenty squares with 1m² were used, in random points to each evaluation. The nylon bag technique was used for litter decomposition evaluation, incubating the following litter fractions: just-fallen leaves, “aging” leaves already deposited and in the beginning of the mineralization, and branches. The incubation periods were 0, 4, 8, 16, 32, 64, 100, and 256 days, being the same procedure carried through in 2006 and 2007. Treatments were distributed in randomized block design with five replications. Leaf deposition reached the value of 15,167 kg OM/ha, presenting greater deposition in the rainy period. Leaves represented the greater proportion of litter deposited, with average ratio of 87% of predominance in the majority of the evaluations. Branches and leaves presented average nitrogen concentration of 1.4% and 2. 7%, respectively, demonstrating that leaves were the maincontributors of nutrients via litter. The C/N ratio of leaves was below 30, branches presented C/N ratio between 30 and 40, likely favoring the nitrogen immobilization by ground microorganisms. The relationship between litter deposition and litter accumulation in the last month of evaluation was 0.30 indicating that it presented greater accumulation than deposition. In the decomposition assay, branches presented lesser mineralization than leaves both for total biomass and nitrogen, with leaf and branch decomposition varying with the incubation periods. The decomposition of substrata was influenced by the rainfall amount occurred in the evaluation period. In a general way, it was concluded that the litter component is essential in the process of nutrient recycling in a sabiá canopy, however, the mineralization occurs in relatively slow taxes, being this fact relevant in the reduction of nutrient losses by leaching, contributing for the maintenance of this ecosystem.