Denitrification Hysteresis During Wetting and Drying Cycles in Soil
- Peter M. Groffman * and
- James M. Tiedje
Denitrification response to soil moisture was studied in soils undergoing either wetting or drying cycles to determine if denitrification-soil water relationships were independent of antecedent moisture conditions. Intact, field moist soil cores were brought into the laboratory and subjected to either wetting or drying phase treatments. In the drying phase treatment, soils were wet to saturation and then progressively dried to field capacity, 60% water-filled porosity and 20% water-filled porosity with denitrification measured at each moisture condition. In the wetting phase treatment, soil cores were first dried to 20% water-filled porosity and were then progressively wet to 60% water-filled porosity, field capacity, and saturation. Denitrification showed a hysteretic response to soil moisture when drying and wetting phases were compared. In the drying phase, rates of denitrification decreased dramatically as soils were dried from saturation to field capacity, with further decreases in activity observed at 60 and 20% water-filled porosity. In the wetting phase, denitrification activity sharply increased immediately after rewetting soils from 20 to 60% water-filled porosity, with only slight increases observed as soils were wet further to field capacity and saturation. The hysteretic response was observed in three soils of markedly different texture. Denitrification dynamics in the wetting phase were strongly correlated with pulses of C and N mineralization caused by stress of microbial biomass by drying and rewetting. Models of denitrification driven by soil moisture need to consider hysteretic effects if they are to accurately predict denitrification activity in the field.
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