Isotopic partitioning of soil respiration components in response to warming and altered precipitation in a grassland ecosystem

Dr Biao Zhu, Dr Weixin Cheng

1Peking University, , China, 2University of California at Santa Cruz, , USA

How the two components of soil respiration, namely rhizosphere respiration and soil organic matter (SOM) decomposition, respond to climate change is important for predicting the feedback between carbon cycle and climate change. In this study, we used the natural abundance 13C tracing technique to partition soil respiration in response to warming and altered precipitation in a grassland ecosystem in Kansas, USA. We grew a common C3 grass (Bromus inermis) in the native C4 grassland soil, and used infrared radiators and rainout shelters to control temperature (ambient and +2ºC) and precipitation (ambient and delayed – increase dry intervals by 50% without changing total amount of rainfall) in the Konza Prairie Biological Station. Results showed that the root-derived CO2 (Ra) was suppressed by delayed rainfall in summer and fall (but not in spring), and was not affected by warming in all three seasons. In contrast, the SOM-derived CO2 (Rh) was enhanced by warming only in fall, and was not affected by delayed rainfall in all three seasons. The rhizosphere priming effect (RPE) was calculated as the difference in Rh between planted area and unplanted root-free area. RPE was minor in spring, but was significant in summer and fall. Moreover, RPE was not sensitive to warming or delayed rainfall in summer, but was stimulated by warming (but unresponsive to delayed rainfall) in fall despite no change in shoot or root biomass. Taken together, these results suggest that the impact of soil warming and altered timing of precipitation on soil CO2 emissions varied with season (spring, summer or fall) and the source of CO2 (Ra, Rh or RPE). This study presents one of the first measurements of RPE from field experiments using non-destructive isotopic tracing techniques and shows that soil warming could enhance the magnitude of RPE in the grassland ecosystem.

Biography: Biao Zhu is an Assistant Professor of Ecology at College of Urban and Environmental Sciences, Peking University. His research interests are rhizosphere processes, soil carbon and nutrient cycling, and global change.

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