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

We investigated how soil temperature (T-s) and water content (VWC) affect soil respiration (R-s) 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 R-s varied from 0.28 to 3.62 mu mol CO2 m(-2) s(-1). Over this period of record, R-s increased exponentially with rising temperature; a Q(10) model with 5-cm soil temperature as the independent variable explained 76% of the variation in half-hourly R-s. The temperature sensitivity of respiration (Q(10)) varied seasonally, being greater in fall than in spring, suggesting seasonal hysteresis in the R-s-T-s relationship. During the summer months (June August 2011), when T-s was high and had relatively little day-to-day variation, R-s was hyperbolically related to VWC, increasing with increasing VWC up to a VWC threshold of 0.17 m(3) m(-3), but decreasing with increasing VWC above the threshold. A bivariate Q(10)-hyperbolical model, which incorporated both T-s and VWC effects, improved the performance of R-s simulation in summer, but not annually. These results indicated that R-s was dominantly controlled by soil temperature over the annual cycle. However, VWC served as the dominant control in summer. The annual total of R-s estimated from the Q(10) model was 475 g C m(-2). We recommend the use of the Q(10) model for predicting annual soil respiration due to its good performance and physiological basis. (C) 2012 Elsevier Masson SAS. All rights reserved.