Andrew Procter1, Alexia M. Kelley1, Philip A. Fay2, Virginia L. Jin2, H. Wayne Polley2, and Robert B. Jackson1. (1) Duke University, (2) USDA, Agricultural Research Service
Background/Question/Methods Changes in soil respiration due to rising atmospheric CO2 have large implications for land-atmosphere carbon balance and consequently the greenhouse effect. We report results from tallgrass prairie exposed to a gradient of CO2 spanning preindustrial to expected mid-century levels (250 - 500ppm). Elongated chambers are used to expose soil monoliths planted to tallgrass prairie species to a CO2 gradient. Three soil series are represented along the CO2 gradient: Austin (mollisol), Bastrop (alfisol), and Houston (vertisol). Soil respiration was measured monthly with an infrared gas analyzer during the 2007 growing season (April – October).
Results/Conclusions Soil respiration responded positively to CO2 treatment on all soils. The response of respiration to CO2 was linear in Bastrop and Houston soils (p < 0.05), but non-linear in Austin soil. Interestingly, of the three soils, Houston and Austin are most similar in texture. There is likely a seasonal dimension to the soil type x CO2 interaction. Early in the growing season (May), linear regressions of respiration rate vs CO2 treatment were not significant, but in July and October were significant (p < 0.05). Averaged across the 2007 growing season, respiration rates were highest on Houston soil and lowest on Austin soil, with Bastrop soil intermediate (8.38, 6.80, and 7.40 μmol CO2/m2/s, respectively). Soil respiration responses, when combined with results on photosynthesis and plant productivity, will allow better characterization of prairie as a C sink or source under future CO2 levels.