PHOSPHORUS SOLUBILIZATION AND POTENTIAL TRANSFER TO SURFACE WATERS FROM THE SOIL MICROBIAL BIOMASS FOLLOWING DRYING-REWETTING AND FREEZING-THAWING

Drying-rewetting and freezing thawing are two of the most common forms of abiotic perturbations experienced by soils, and can result in the solubilization of phosphorus (P). There is increasing interest in one particular component of soil P that may be especially susceptible to such stresses: the soil microbial biomass. We examine the evidence for the soil microbial biomass acting as a significant source of P in soils and surface waters by studying the literature on the processes responsible for its solubilization and transfer, resulting from abiotic perturbations. These perturbations have been shown to kill up to circa 70% of the total microbial biomass in some soils, and in some cases nearly all the additional P solubilized has been attributed to the microbial biomass. The degree to which the soil microbial biomass is affected by abiotic perturbations is highly dependent upon many variables, not the least degree, duration, and temporal patterns of stress, as well as the soil type. It is hypothesized that while abiotic perturbations can solubilize large quantities of P from the soil microbial biomass in some soils, only a small proportion is likely to find its way from the soil to surface waters. This is not to say that this small proportion is not significant with regard to surface water quality and nutrient loss from the soil, and may become more prevalent under future climatic change. We conclude that it is likely that only extreme conditions will elicit large responses with regard to the solubilization and transfer of phosphorus to surface waters.