GENDER DEPENDENT INFLUENCES ON SOIL-PHOSPHORUS BY THE DIOECIOUS LOWLAND TROPICAL TREE SIMAROUBA-AMARA

We compared soil phosphorus levels below canopies of the lowland tropical rain forest tree species Simarouba amara Aubl. with soil sampled beyond the edge of S. amara canopies. Our data show that trees affect soil phosphorus concentrations and that differences below individual trees are related to gender for this dioecious species. Soil sampled adjacent to female trees had significantly higher soil phosphorus levels for several different indices of phosphorus availability than soil sampled beyond tree crowns. Male trees did not significantly modify soil phosphorus levels. Analysis of total mineral phosphorus (Total-phosphorus) below and beyond the canopies of male and female of S. amara found no differences in the total amount of phosphorous combined within bound and labile soil fractions. We measured a small increase in soil organic matter under tree canopies, but found no gender-related difference. Our results indicate that increased phosphorus availability beneath female S. amara arises from a gender-related modification in phosphorus cycling rather than from higher recruitment of females on sites rich in phosphorus or organic matter. We suggest that gender-dependent controls on soil phosphorus may include below-canopy enrichment of available phosphorus due to fruit and litter cycling or increases in phosphorus transformation from bound to labile forms.