Biogeochemical implications of labile phosphorus in forest soils determined by the Hedley fractionation procedure.
Forest ecologists and biogeochemists have used a variety of extraction techniques to assess labile vs. non-labile soil P pools in chronosequences, the balance between biological vs. geochemical control of P transformations across a wide range of soil orders, the role of plants with either N-fixing or mycorrhizal symbionts in controlling soil P fractions, and to make inferences about plant-available P. Currently, variants of the sequential extraction procedure developed by M. J. Hedley and co-workers afford the greatest discrimination among labile and non-labile organic and inorganic P pools. Results of recent studies that used this technique to evaluate P fractions in forest soils indicate the following: (1) in intact, highly weathered forest soils of the humid tropics, Hedley-labile P values are several times larger than extractable P values resulting from mildly acidic extracting solutions which were commonly used in the past 2 decades; (2) pools of Hedley-labile P are several times larger than the annual forest P requirement and P required from the soil annually in both temperate and tropical forests; (3) long-term trends in non-labile P pools during pedogenesis are adequately represented by the Walker and Syers' model of changes in P fractionation during soil development. However, to better represent trends in pools that can supply plant-available P across forest soils of different age and weathering status, the paradigm should be modified; and (4) across a wide range of tropical and temperate forest soils, organic matter content is an important determinant of Hedley-labile P.
Johnson
Arthur H
AH
Department of Earth and Environmental Science, The University of Pennsylvania, 240 S. 33rd St., Philadelphia, PA 19104-6316, USA. ahj@sas.upenn.edu
Frizano
Jaqueline
J
Vann
David R
DR
D005591:Chemical Fractionation / Q000379:methods*; D008962:Models, Theoretical; D010758:Phosphorus / Q000032:analysis*; D012987:Soil / Q000032:analysis*; D014197:Trees
D012987:Soil; D010758:Phosphorus