Abstract: Canopy stomatal conductance is an important parameter in eco-hydrological studies. To understand its responses to environmental factors can offer theoretical basis for developing mechanism-based models of forest transpiration. In this paper, Granier’s probe was adopted to measure the sap flow of a Larix princips-rupprechtii stand in a small watershed of Diediegou in northern part of Liupan Mountains from May to September 2005, and the related environmental factors were simultaneously observed. The canopy transpiration (E_c) and mean canopy stomatal conductance (g_c) were calculated, and the observed data were fitted by the Jarivs-type model of canopy stomatal conductance. Then, the responses of g_c to environmental factors such as photosynthetically active radiation (PAR), vapor pressure deficit (DVP), and relative extractable soil water (REW) were analyzed. The results showed that Jarivs-type model could accurately simulate the diurnal variation patterns of g_c. The coefficient of determination (R²) between calculated and simulated g_c was 0.76 (n= 952). The g_c had different responses to environmental factors in a non-linear way. PAR was the driving factor for g_c, with the driving effect being stronger when the PAR was <0.35mmol·m^-2·s^-1 while weaker when the PAR was above this threshold. DVP was a limiting factor for g_c which decreased with increasing DVP. The response of g_c to REW varied. When the REW was less than 41%, it was a key restricting factor to g_c; when the REW was higher than 41%, its restricting effect became weaker.

Key words: Rice, Canopy, Spectral characteristics