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Evaluating the influence of aboveground production on grassland soil respiration in Central Iowa, U.S.A.
Dornbush, Mathew*,1, Raich, James1, 1 Iowa State University, Ames, IA
ABSTRACT- Globally, soil respiration rates correlate positively with mean annual temperature and precipitation. Under similar climates, differences in vegetation and land use produce notable differences in soil respiration. While consideration of these factors is important for predicting soil respiration, unexplained site-to-site variation within systems still remains. To improve our understanding of the factors contributing to this variation, we tested the hypothesis that within-system, site-to-site differences in soil respiration rates result from differences in aboveground plant production. We addressed this hypothesis by measuring soil temperature, soil moisture, aboveground net primary production (ANPP), and end of year root biomass at four Central Iowa riparian grasslands growing on the same soil series, from May 2001 through May 2002. Annual soil respiration rates ranged from 730 to 1,300 gC m-2, while ANPP ranged from 760 to 1800 gOM m-2. Annual soil respiration rates were poorly correlated with ANPP, however a stronger relationship between annual soil respiration and end-of-season root biomass was found. Neither live aboveground biomass nor net primary production rate were significant terms in seasonal models. When growing season data (April to September) was considered alone, the importance of live aboveground biomass increased, accounting for roughly 5% of model-explained variation. Our results suggest that while aboveground production may be an important predictor of annual soil respiration rates, this effect does not appear to be independent of belowground biomass at the spatial scale of this project. Furthermore, correlations between changes in soil temperature and aboveground biomass, and the prolonged winter dormant season appear to limit aboveground production's explanative potential for seasonal changes in soil respiration.
Key words: soil respiration, temperate grasslands, aboveground production