Reproductive output and biomass allocation in Sesbania emerus in a tropical swamp.

Examined Sesbania emerus, an annual legume growing along a moisture gradient in a swamp in Guanacaste Province, Costa Rica. Morphological changes included production of more stems and branches in response to herbivory, more and higher prop roots and more aerenchyma as water depth increased, and greater stem diameter in lower densities. Plant height varied greatly within a site, but not among habitats. Plants began to produce flowers and fruits later in wet sites. Reproductive output was generally more sensitive to environmental variables than was plant size. Great fruit and seed production were correlated with drier sites, earlier phenology, and lower density, but not with herbivory. Total biomass accumulation did not vary among moisture sties, but root production appeared to occur at the expense of reproductive output in the wetter sites. Plants in the wetter sites had both a greater percent and a greater absolute amount of biomass in roots, and a lower percent and a lower absolute amount of biomass in fruits and seeds than plants in drier sites. Seed number per plant ranged from a mean of 6800 at the wet site to 16 878 at the dry site.-from Authors