Vertical distribution of biological and geochemical phosphorus subcycles in two southern Appalachian forest soils

We measured Al, Fe, and P fractions by horizon in two southern Appalachian forest soil profiles, and compared solution PO4^-1 removal in chloroform-sterilized and non-sterilized soils, to determine whether biological and geochemical P subcycles were vertically stratified in these soils. Because organic matter can inhibit Al and Fe oxide crystallization, we hypothesized that concentrations of non-crystalline (oxalate-extractable) Al (Al0) and Fe (Fe0), and concomitantly P sorption, would be greatest in near-surface mineral (A) horizons of these soils. Al0 and Fe0 reached maximum concentrations in forest floor and near-surface mineral horizons, declined significantly with depth in the mineral soil, and were highly correlated with P sorption capacity. Small pools of readily acid-soluble (AF-extractable) and readily-desorbable P suggested that PO4^3- was tightly bound to Al and Fe hydroxide surfaces. P sorption in CHCl3-sterilized mineral soils did not differ significantly from P sorption in non-sterilized soils, but CHCl3 sterilization reduced P sorption 40-80% in the forest floor. CHCl3 labile (microbial) P also reached maximum concentrations in forest floor and near-surface mineral horizons, comprising 31-35% of forest floor organic P. Combined with previous estimates of plant root distributions, data suggest that biological and geochemical P subcycles are not distinctly vertically stratified in these soils. Plant roots, soil microorganisms, and P sorbing minerals all reach maximum relative concentrations in near-surface mineral horizons, where they are likely to compete strongly for PO4^3- available in solution. © 1991 Kluwer Academic Publishers.

Duke Scholars

Author Curtis J. Richardson Environmental Natural Science