Wednesday, August 8, 2007 - 10:30 AM

COS 61-8: Soil CO2 efflux and plant production across a chronosequence of tallgrass prairie reconstructions, Iowa, USA

Ryan M. Maher1, Heidi Asbjornsen1, and Randall K. Kolka2. (1) Iowa State University, (2) USDA Forest Service, North Central Research Station

An understanding of soil CO2 efflux and plant biomass production in tallgrass prairies planted into formerly cultivated ecosystems is critical if we are to predict the effects of grassland reconstructions on belowground carbon dynamics. In addition, it is important to assess the climatic and biological controls on soil CO2 efflux across a landscape of cultivated and reconstructed grassland ecosystems to improve predictions to climate change. This study used a 12 yr chronosequence of tallgrass prairie reconstructions in central Iowa, including a no-till soybean field (time = 0), to quantify the relationship between tallgrass prairie age, soil CO2 efflux, standing root biomass, aboveground net primary productivity, and root production. We also assessed the strength and interaction of soil temperature and soil moisture in predictions of soil CO2 efflux across the chronosequence. Linear regressions showed a significant increase in standing root biomass (R2 = 0.88) and growing season soil CO2 efflux (R2 = 0.83) with prairie age while changes in above and belowground production were less predictable. Growing season soil CO2 efflux ranged from 624 gC m-2yr-1 in a soybean cropping system to 939 gC m-2yr-1 in the oldest reconstruction (12 yr). Among all tallgrass prairie reconstructions there was a strong, positive relationship between soil temperature and soil CO2 efflux (R2 = 0.79) while the effect of soil moisture was greatest for the youngest prairie (age 4). Soil temperature was less correlated with soil CO2 efflux in the no-till soybean field (R2 = 0.36) and the inclusion of soil moisture added limited additional predictive power (R2 = 0.41). Our results indicate that the increase in soil CO2 efflux with reconstruction age is related to the interaction of soil temperature with the accumulation of root biomass in early grassland development.

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