Decomposition and nutrient release from leaf litter in pure and mixed stands of native tree species in southeastern Bahia State, Brazil

Leaf litter decay rates and N and P fluxes of tree species are different in pure and mixed stands because the decomposition process is not only defined by the quality of the substrate, but of the microenvironment (forest production systems) also. The objetive of this work was to estimate the decomposition rate and N and P release from leaf litter of native forest species planted under two different systems. Twenty two year-old mixed and pure stands of six hardwood species (Peltogyne angustiflora, Centrolobium robustum, Arapatiella psilophylla, Sclerolobium chrysophyllum, Cordia trichotoma, Macrolobium latifolium) native of the southeastern region of Bahia, Brazil, were evaluated. As reference for the analyzed characteristics, the study included a secondary forest near climax, and a 40- year-old naturally regenerated forest. The decomposition of leaf litter in sacks of I mm mesh was observed during one year. The single exponential model provided the best adjustment for all species in both planting systems (pure and mixed). Leaf litter decay rates of Peltogyne angustiflora and Macrolobium latifolium were significantly higher in the mixed than in the pure stand of the same species, unlike observed for Arapatiella psilophylla. The leaf litter decay rates of Centrolobium robustum, Sclerolobium chrysophyllum, and Cordia trichotoma were not altered significantly. Not N, but P limited the litter decomposition of these species most. The release of N and P from leaf litter of each species varied according to the microenvironment. Among the heterogeneous ecosystems, the leaf litter decay rate in mixed stands was the only one that differed significantly from the native forest. The highest N release occurred in the mixed stand, whereas P release was clearly lowest in the regenerated forest. It was inferred that mixed stands of forests species own a greater capability of recycling organic matter and nutrients. This indicates that the decay and mineralization processes are not only influenced by the substrate quality, but also the quality of the microenvironment. Information about these processes obtained in pure stand systems should therefore not be extrapolated to heterogeneous forest systems.