ROOT PROLIFERATION IN RECENT AND WEATHERED SANDY SOILS FROM VERACRUZ, MEXICO

Field observations and laboratory experiments on unweathered and weathered dune sand beneath a tropical deciduous forest in Veracruz, México were used to test the hypothesis that temporary nutrient adsorption by more weathered soil facilitates more effective nutrient recycling through the stimulation of a superficial fine root system. An analysis of soil solution composition in the field indicated that K, P and NO3--N were being more effectively retained in weathered sand topsoil than in recent sand but, in a leaching experiment, only NO3--N was more effectively adsorbed by this soil. Fine roots in weathered sand were more concentrated superficially than in recent sand, and a bioassay with seedlings of Cedrela odorata showed more fine root proliferation in this medium than in recent sand. In combination, these data suggest that weathering of sand in this area promotes an increased nitrate adsorption capacity which may stimulate greater root proliferation in topsoils and lead to the entrainment of other nutrients in a more concentrated topsoil-vegetation cycle. If these results can be applied to the larger domain of tropical soils generally, they suggest that nitrate adsorption may play an important role in stimulating effective nutrient recycling by forests occupying weathered soils. © 1990, Cambridge University Press. All rights reserved.