Abstract
The proportion of microbial biomass-C released into the soil environment following rapid water potential increase was quantified in two soils using a modified chloroform-fumigation biomass assay. Dry samples were isopiestically equilibrated to −2.8 and − 6.9 M Pa and then wetted to field capacity with either H 2O or KCl solutions. The KC1 solutions wetted the soils without altering total soil water potential. The biomass-C released by water potential increase ranged from 17 to 70% of total, depending on the soil, the magnitude of the increase, and the method of calculation. In both soils, a greater proportion of biomass-C was released following a 6.9 MPa than a 2.8 M Pa increase. Biomass-C release was also demonstrated by an increase in soluble organic C in leachates of soils subjected to rapid wetting. Respiration of biomass-C mobilized by water potential increase exceeded respiration of biomass-C made available by preceding desiccation, thereby comprising a significant component of the pulse of respiration observed following wetting of dry soil. Water potential increases associated with the wetting of dry soil may be a major catalyst for soil C turnover.
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