See more from this Session: General Soil and Environmental Quality Posters: II
Wednesday, October 19, 2011
Henry Gonzalez Convention Center, Hall C, Street Level
Sensitivity of CO2 efflux from soil organic matter (SOM) decomposition to temperature is a pivotal parameter in global C cycle models. Under field conditions factors such as soil moisture, O2 and CO2 contents interact with SOM temperature sensitivity possibly leading to different temperature responses than anticipated from biochemical kinetics. At the soil profile scale, driving factors can change independently with depth, making a depth-specific assessment of temperature sensitivity essential. The objectives of this study were to assess 1) the temporal variation of CO2 production at different depths and the contribution of subsoil CO2 production to total soil respiration and 2) the controlling factors of SOM decomposition and its temperature sensitivity at different depths. We measured CO2, O2, temperature, and soil water content (θ%vol) in two plots at 15, 30, 50, 70, and 90cm depths at the University of California student farm in Davis from April, 2008 till September 2009. We calculated CO2 flux and concentration gradients and compared temperature sensitivity between top and subsoil by fitting an exponential Q10 model to the data. The A horizon had the largest daily CO2 fluctuations (average CO2 concentration =0.2%) during spring and winter whereas in the C2 horizon, CO2 production (average CO2 concentration =0.8%) followed the soil temperature variation, with lowest CO2 production in winter and highest in summer. Under non-limiting moisture (θ>20%) the Q10 value for the A horizon was 5.33 (0.93µmol CO2 m3 s-1) decreasing to 1.29 (0.57µmol CO2 m3 s-1) at θ<10%. In the C2 horizon at θ>20%, Q10 was 3.13 (0.19µmol CO2 m3 s-1) indicating that it is less sensitive to temperature variations than topsoil when moisture is non-limiting. Moisture content in the subsoil did not decrease below 15% and Q10 was 1.85 (0.45µmol CO2 m3 s-1) at this moisture. In conclusion, this study showed decreasing temperature sensitivity with soil depth and that under Mediterranean conditions, CO2 production from subsoils is important in determining soil CO2 efflux.