NUTRIENT FLUX AND RETENTION IN A TROPICAL SAND-DUNE SUCCESSION

The input to soils of nutrients in solution, and the output from them in percolating water, were computed over a 3-month period in four stages of a sand-dune succession in Veracruz, Mexico. The first 3 stages occur upon recent sand and represent a succession from pioneer communities to forest. The 4th is forest on a much older fossil dune. The quantity of nutrients entering the soil increased from the pioneer to the forest community on recent sand, but outputs from these systems increased even more rapidly. This declining effectiveness of retention is attributed to mobilization of cations by increased quantities of bicarbonate anions beneath the larger biomass communities. On the fossil dune, nutrient outputs in percolating water were much lower despite large inputs and comparable water fluxes, attributed to soil changes induced by weathering, especially lower pH and the development of an anion exchange capacity. Biological mechanisms of nutrient retention may be relatively ineffective at conserving nutrients unless coupled to a soil adsorption system that temporarily suppresses acute leaching in percolating water. -Authors