Litter decomposition under a sabia canopy in the Forest Zone in Pernambuco

The research aimed to evaluate the decomposition of sabia (Mimosa caesalpiniifolia Benth) litter fractions by using the nylon bag technique. The following litter fractions were incubated: senescent leaves, leaves at the beginning of mineralization, and branches with diameter up to 20 mm. Incubation was performed during periods of 0, 4, 8, 16, 64, 100, and 256 days in 2006 and 2007. The fractions were distributed in a random block design with five replications. It was evaluated the disappearance of biomass, nitrogen (N), and phosphorus (P), concentrations of nitrogen and phosphorus and the carbon/nitrogen ratio of litter during the periods of incubation. In general, the negative exponential model explained the disappearance of biomass, nitrogen, and phosphorus, however, there was a variation among years and, in some cases, despite of being significant, the models showed a low correlation between predicted and observed data. Biomass disappearance rate was slow because only 30% of leaf biomass was mineralized after 256 days of incubation. Net nitrogen mineralization showed large variation among years, and it differed among the studied fractions. Nitrogen content of the litter increased, on average, until 32 days (leaves) and until 64 days (branches) of incubation followed by stabilization. The linear plateau model was used to explain that process. In the course of the incubation periods, the carbon/nitrogen ration decreased. Despite of the high content of nitrogen, the decomposition of sabia litter is slow, what might reduce the loss of nutrients in the forest, increasing its sustainability and reducing the possible deleterious effects to the environment.