Relationship between soil P fractions and microbial biomass in an oligotrophic grassland-desert scrub system

Phosphorus (P) is an essential element of the biosphere, both as a constituent of living organisms and as a regulator of biological processes. The Cuatro Ci,negas Basin in the central Chihuahuan Desert of Mexico is characterized by extreme P oligotrophy. The aim of this study was to quantify P distribution in soil P fractions, P sorption capacity, and P in microbial biomass in a desert scrub and grassland soil system in the Churince area of the Cuatro Ci,negas Basin over summer and winter seasons. Our objective, as part of an exploration of ecosystem functioning, was to ascertain the relationship between soil P fractions and P in microbial biomass. Our results demonstrate a scarcity of P, mainly in grassland, and also a higher P sorption capacity in grassland soil than in desert scrub. Desert scrub soil retained more P (228 +/- A 5 mu g g(-1) dry soil) than grassland soil (87 +/- A 10 mu g g(-1) dry soil), mainly in inorganic forms, but grassland soil retained more P in accessible organic forms. We suggest that biotic controls regulated by access to water shape the dynamics of soil P availability in the Churince grassland-desert scrub system.