Soil respiration in a mixed urban forest in China in relation to soil temperature and water content

We investigated how soil temperature (Ts) and water content (VWC) affect soil respiration (Rs) in a mixed urban forest. Continuous half-hourly measurements of soil surface efflux were made during the period March–December 2011 in a mixed forest in Beijing Olympic Forest Park, China. Daily mean Rs varied from 0.28 to 3.62 μmol CO2 m−2 s−1. Over this period of record, Rs increased exponentially with rising temperature; a Q10 model with 5-cm soil temperature as the independent variable explained 76% of the variation in half-hourly Rs. The temperature sensitivity of respiration (Q10) varied seasonally, being greater in fall than in spring, suggesting seasonal hysteresis in the Rs–Ts relationship. During the summer months (June–August 2011), when Ts was high and had relatively little day-to-day variation, Rs was hyperbolically related to VWC, increasing with increasing VWC up to a VWC threshold of 0.17 m3 m−3, but decreasing with increasing VWC above the threshold. A bivariate Q10-hyperbolical model, which incorporated both Ts and VWC effects, improved the performance of Rs simulation in summer, but not annually. These results indicated that Rs was dominantly controlled by soil temperature over the annual cycle. However, VWC served as the dominant control in summer. The annual total of Rs estimated from the Q10 model was 475 g C m−2. We recommend the use of the Q10 model for predicting annual soil respiration due to its good performance and physiological basis.

► In this study we monitor the soil surface respiration in a mixed urban forest in Beijing. ► Soil respiration increased exponentially with rising temperature annually. ► Soil respiration in spring and fall was dominantly controlled by soil temperature. ► Soil respiration was significantly, hyperbolically affected by VWC in summer.