, Volume 52, Issue 2, pp 155-172

Biological and geochemical controls on phosphorus fractions in semiarid soils

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Abstract

This study examined the concentration of organic and inorganicphosphorus in surface soils of a Boutelouagracilis-Bouteloua eriopoda grassland, and a Larreatridentata shrubland, in the northern Chihuahuan Desert, NewMexico, U.S.A. In this desert where the grassland vegetation has auniform spatial distribution and individual shrubs have a patchy spatialdistribution across the landscape, vegetation strongly influences thedistribution of soil nutrients. Most studies of soil phosphorusfractions in desert soils have focused primarily on inorganic Pfractions and have demonstrated the importance of geochemical controlson soil P cycling. The research presented here addressed the question ofwhether organic phosphorus, determined by the presence of differentvegetation types, also contributes to soil P cycling. Within soils ofsimilar age, topography, parent material, and climatic regime, sampleswere collected under and between vegetation and analyzed for P fractionsfollowing a modified sequential fractionation scheme. Most soilinorganic P was found in the HCl- and cHCl-extractable forms in both thegrassland and shrubland soils, indicating CaCO3 control overphosphorus availability. In contrast, most soil organic P was bound toAl and Fe minerals. Labile, plant-available P fractions summed to9.5% of total P in the grassland and 6.1% in theshrubland. Organic P comprised 13.3% of the total phosphorus poolin the grassland and 12.0% in the shrubland. Our results showthat the organic P pool may represent an important, yet oftenoverlooked, source of P in semiarid ecosystems.