Source components and interannual variability of soil CO₂ efflux under experimental warming and clipping in a grassland ecosystem

Partitioning soil CO 2 efflux into autotrophic ( R A ) and heterotrophic ( R H ) components is crucial for understanding their differential responses to climate change. We conducted a long‐term experiment (2000–2005) to investigate effects of warming 2°C and yearly clipping on soil CO 2 efflux and its components (i.e. R A and R H ) in a tallgrass prairie ecosystem. Interannual variability of these fluxes was also examined. Deep collars (70 cm) were inserted into soil to measure R H . R A was quantified as the difference between soil CO 2 efflux and R H . Warming treatment significantly stimulated soil CO 2 efflux and its components (i.e. R A and R H ) in most years. In contrast, yearly clipping significantly reduced soil CO 2 efflux only in the last 2 years, although it decreased R H in every year of the study. Temperature sensitivity (i.e. apparent Q 10 values) of soil CO 2 efflux was slightly lower under warming ( P >0.05) and reduced considerably by clipping ( P <0.05) compared with that in the control. On average over the 4 years, R H accounted for approximately 65% of soil CO 2 efflux with a range from 58% to 73% in the four treatments. Over seasons, the contribution of R H to soil CO 2 efflux reached a maximum in winter (∼90%) and a minimum in summer (∼35%). Annual soil CO 2 efflux did not vary substantially among years as precipitation did. The interannual variability of soil CO 2 efflux may be mainly caused by precipitation distribution and summer severe drought. Our results suggest that the effects of warming and yearly clipping on soil CO 2 efflux and its components did not result in significant changes in R H or R A contribution, and rainfall timing may be more important in determining interannual variability of soil CO 2 efflux than the amount of annual precipitation.