Individual- and stand-level stem CO sub(2) efflux in a subtropical Schima superba plantation

Stem respiration is an important, but poorly studied component of total forest ecosystem respiration. Stem CO sub(2) efflux was investigated with an open gas exchange system while stand microclimate and stem temperature were continuously monitored in a Schima superba plantation in South China for several days in August and December 2010. The temperature response of respiration in the different seasons, the vertical variation in stem CO sub(2) efflux along the stem, and the stand-level stem CO sub(2) efflux were examined. Stem volume was identified as the better correlate for stem CO sub(2) efflux and was used as the scalar for the stand-level estimates of stem CO sub(2) efflux in this S. superba plantation. Volume-based stem CO sub(2) efflux was higher at 2 m than at 1.3 m. Mean stem CO sub(2) efflux was 268.9 and 104.6 mu mol m super(-3) s super(-1) in August and December, respectively, indicating a dramatic seasonal variation of stem CO sub(2) efflux. The temperature response of stem CO sub(2) efflux remained constant during our study period with Q sub(10) values of 1.9 and 1.8. In this subtropical S. superba plantation, stem CO sub(2) efflux per unit ground area averaged 3.36 and 1.26 mu mol m super(-2) s super(-1) based on the measurement data at 1.3-m height of the stem in August and December, respectively. Our results suggest that stem CO sub(2) efflux has a constant temperature response, and the seasonal variation in stem CO sub(2) efflux is mainly controlled by stem temperature, and the vertical variation in stem CO sub(2) efflux needs to be considered in the stand-level estimation.