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Soil respiration and microbial biomass in subhumid temperate grassland: Role of fire and simulated grazing.
Harris, Wylie*,1, Boutton, Thomas1, Ansley, R.1, 1 Texas A&M University, College Station, Texas
ABSTRACT- Soil carbon (C) dynamics in grassland ecosystems depend on interactions between climate, litter quantity/quality, soil characteristics, and management. We tested the hypotheses that turnover of C is 1) accelerated by grazing, and 2) reduced by fire, in southern Great Plains grasslands. Seven factorial combinations of fire and simulated grazing (clipping) were applied to replicated plots. Prescribed fires were conducted in winter (Feb/Mar) or fall (Oct/Nov). Simulated grazing consisted of light or continuous clipping. Soil moisture and temperature, soil respiration, and soil microbial biomass (SMB) were measured monthly. Seasonal climatic variation had the greatest influence on all response variables. Within that climatically-determined context, season of fire and clipping affected mean monthly plant and soil responses relative to controls. Soil moisture decreased in winter fire and spring clipping treatments, and soil temperature increased under winter fires. Soil microbial biomass decreased in winter fire treatments (381 mg C kg soil -1) relative to controls (424 mg C kg soil -1). Soil respiration showed no treatment effects. These preliminary results support the hypothesis that fire reduces microbially-mediated soil C turnover, though the lack of significant response to clipping is contrary to expectations. Nonsignificant reductions in soil respiration and SMB under all fire and clipping treatments suggest that removal of aboveground plant material may limit microbial biomass by reducing the C substrate available to support microbial activity.
KEY WORDS: soil respiration, microbial biomass, fire, grazing