Individual- and stand-level Stem CO<sub>2</sub> efflux in a subtropical <i>Schima superba</i> plantation
Abstract. Stem CO2 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 over the different seasons, the vertical variation in stem CO2 efflux along the stem and the stand-level stem CO2 efflux were examined. Stem volume was identified as the better correlate for stem CO2 efflux and was used as scaling scalar for the stand-level estimates of stem CO2 efflux in this S. superba plantation. Volume-based stem CO2 efflux was higher at 2 m than at 1.3 m. Mean stem CO2 efflux was 268.9 and 104.6 μmol m−3 s−1 in August and December, respectively, indicating a dramatic seasonal variation of stem CO2 efflux. The temperature response of stem CO2 efflux was constant during our study period with Q10 values of 1.9 and 1.8. In this subtropical S. superba plantation, the averaged stem CO2 efflux per unit ground area was 3.36 and 1.26 μmol m−2 s−1 in August and December, respectively, which was underestimated due to the vertical variation of stem CO2 efflux along the stem. Our results suggest that stem CO2 efflux has a constant temperature response on the stand scale, and the seasonal variation in stem CO2 efflux is mainly controlled by stem temperature, and the vertical variation in stem CO2 efflux needs to be considered at the stand-level estimation.