Tuesday, August 3, 2010: 9:00 AM
406, David L Lawrence Convention Center
E. Carol Adair, Rubenstein School of Environment and Natural Resources, University of Vermont, Burlington, VT, Peter B. Reich, Department of Forest Resources, University of Minnesota, St. Paul, MN, Jared Trost, USGS MN Water Science Center, Mounds View, MN and Sarah E. Hobbie, Department of Ecology, Evolution, and Behavior, University of Minnesota, Saint Paul, MN
Background/Question/Methods Elevated CO2 consistently increases soil respiration, the primary pathway for the return of organic carbon (C) to the atmosphere, but uncertainties exist about the cause of this increase. Increasing atmospheric CO2 may increase soil respiration (SR) by increasing plant and microbial C availability via increased photosynthesis and belowground C inputs or by increasing soil water availability via CO2-induced declines in stomatal conductance and plant water use. Furthermore, other global change factors may affect these drivers of SR, interacting with CO2 to increase or decrease SR. We therefore took concurrent measurements of SR and volumetric soil water content (VSWC) throughout a growing season in the Biodiversity, CO2, and N (BioCON) experiment, with the goals of determining the interacting effects of these factors on SR and VSWC and discovering the mechanism(s) behind the effect of elevated CO2 on SR.
Results/Conclusions
Elevated CO2 had the largest effects on VSWC and SR, increasing both by as much as 100%. Diversity and N had small, mostly negative effects on VSWC. Surprisingly, diversity did not affect SR. Nitrogen had a small positive effect on SR that was unrelated to its effect on VSWC. On most – but not all – days, the effect of CO2 on SR increased with the effect of CO2 on VSWC. Additionally, the effect of CO2 on SR was largest during dry periods. Thus, our results indicate that while a portion of the large positive response of SR to CO2 was associated with CO2-induced increases in VSWC, this association was temporally variable. Yet CO2-induced changes in soil moisture failed to explain between 40-100% of the CO2 effect on SR (depending on day and the size of the CO2 effect on soil moisture). Additionally, elevated CO2 increased SR across all levels of VSWC, suggesting a role for increased substrate availability in driving the stimulation of SR by elevated CO2, and providing further support for increased rates of C cycling at elevated CO2.
