Abstract:In order to understand water use characteristics of Schima superba plantation and their relationships with environmental factors, Granier’s thermal dissipation probes were applied to measure sap flow density of 15 trees in a typical plantation stand, in which environmental factors including photosynthetically active radiation (PAR), air relative humidity, air temperature and soil moisture were recorded synchronously. Stand transpiration (Jd) and canopy stomatal conductance (gs) were then calculated based on sap flow density, sapwood area, environmental humidity and temperature from December 2007 (dry season) and September 2008 (wet season). The results showed that trees with larger sapwood areas had greater contribution of stand transpiration. Jd was found to be significantly different during wet and dry seasons, which had an average of 21.1 g H2O s-1 in September but only 7.03 g H2O s-1 in December, indicating a dramatic seasonal variation of it. In the meantime, Jd was found to be significantly correlated with environmental factors, in which PAR had the largest correlation coefficient and followed by vapor pressure deficit (VPD), air relative humidity and air temperature in sequence. On the other hand, the maximum gs were calculated to be 30.8 mmol m-2s-1 and 19.7 mmol m-2s-1 in September and December, respectively. It had positive linear relationship with PAR but negative one with VPD when PAR was larger than 1000 μmol m-2s-1 and VPD was over 2 kPa. However, gs did not present any statistically significant relation with soil moisture either in July or December, indicating that soil moisture was not the major environmental factor influencing stand transpiration of S. superba during our study periods.
