Phosphorus pools in tree and intercanopy microsites of a juniper-grass ecosystem

Gradients of soil-nutrient distribution between trees and intercanopy areas are common in many semiarid woodland ecosystems. To test if microsites und er and between canopies influenced P pool distribution in a semiarid woodla nd dominated by one-seed juniper [Juniperus monosperma (Engelm,) Sarg,] and galleta grass [Hilaria jamesii (Torr,) Benth,], we compared inorganic, org anic, and microbial P peals under trees and intercanopy areas of two Aridis ols, Soils collected (5-15 cm depth) under eight tree canopies and in eight intercanopy areas from a Calciorthid and a Camborthid were subjected to a sequential P fractionation scheme. Soils and microsites were significant in dependent factors determining total soil P, which ranged from 814 mu g P g( -1) soil (SE = 25) to 1123 mu g P g(-1) soil (SE = 21). Resin P was signifi cantly influenced by the interaction of soils with microsite. Organic hydro xide P was the largest organic P fraction and exceeded or equaled the amoun t of resin P, It differed significantly between the Calciorthid at 10.1 mu g P g(-1) soil (SE = 1.0) and the Camborthid at 22.1 mu g P g(-1) soil (SE = 1.6). Microsite and soil did not significantly affect microbial P, which ranged from 12.9 mu g P g(-1) soil (SE = 2.1) to 17.0 pg P g(-1) soil (SE = 0.7), Nutrients and microbial activity are usually concentrated under cano pies in semiarid and arid ecosystems, This research shows that P pools dist ribution in the studied ecosystem did not follow this general pattern, and that soils may be more important in determining P pool distribution than mi crosites.