Consequences of habitat heterogeneity for availability of nutrients in a dry tropical forest

Abstract

1 This study evaluates the consequences of habitat heterogeneity in terms of patchy availability of nutrients in a dry tropical forest. The forest floor was characterized by the presence of topographic depressions; litter accumulation in these troughs gives rise to patchy microsites which are different in appearance from the adjoining non-patchy milieu (flats). 2 Litter mass and decomposition were significantly greater in the troughs than in the flats. Decomposition of 95% of the leaf litter needed 488 days in the troughs compared to 576 days in the flats. 3 Troughs were characterized by higher levels of microbial biomass and available nutrient pool. N-mineralization rates were also higher in the troughs. C, N and P concentrations in microbial biomass were positively correlated with N-mineralization rate when data for flats and troughs were pooled. The study indicated that immobilization and release of nutrients occurred in different parts of the year. 4 Fine roots were concentrated in the troughs with the net fine root production of 488 g m^-1 compared to 218 g m^-1 in the flats. Fine root biomass was positively correlated with the concentrations of mineral N and available P in the troughs. N-mineralization explained 46-63% variability in fine root biomass in the microsites. 5 The troughs supported greater herbaceous shoot biomass, particularly in the rainy season, thus preventing leaching by immobilizing excess nutrients. Herbaceous shoot biomass was positively correlated with N-mineralization and mineral N throughout the growing season and across the fertility gradient. 6 Troughs, which accumulated litter and trapped the nutrients in the dynamic microbial biomass, were characterized by higher amounts or organic C, total and mineral N, available P and nutrient supply potential. These areas attracted fine roots to support tree growth, compensated for nutrient limitation and sustained a fairly high level of net primary production in otherwise nutrient poor, leached, impoverished and shallow soil milieu.