Multi-year trend and interannual variability in soil respiration measurements collected in an urban forest ecosystem in Beijing, China

Understanding the long-term trend and interannual variability in soil respiration (Rs) and their controlling factors, is essential to the prediction of soil carbon (C) losses in response to climate change. Knowledge in this field, however, particularly in urban forests remains largely absent. In this study, we analyzed long-term trends in continuous soil CO2 efflux and site-specific climatic data collected in an urban forest plantation in Beijing, China, over a 9-year period (i.e., 2011-2019). Collectively, annual Rs displayed an increasing trend over the study period with a rate of change of 4.31% per year, being strongly affected by changes in soil temperature (Ts). Annual Rs ranged from 447.59 to 622.79 g C m- 2 year-1, yielding a coefficient of variation of 11.26%. Interannual variability in detrended Rs was largely controlled by spring precipitation (PPT), which likely modified Rs by influencing the thawing cycle in soils. The role of soil water content (SWC) in affecting Rs was assessed to be less important. A two-factor linear model combining spring PPT and annual mean Ts performed reasonably well in explaining annual Rs, producing a R2 of 0.55. This study identified different controls for trend and variation in Rs and the findings have important implications in the process-based modeling of soil C emissions in the area.