Abstract: To understand the responses of forest canopy stomatal conductance to environmental factors and the underlying mechanism of canopy stomatal conductance controlling forest transpiration, the Granier thermal dissipation probe technology was used to monitor the sap flow of Platycladus orientalis, a typical tree species of protective forest in Hedong sandy land of Ningxia, from July to September. The microclimate variables were synchronously monitored. Based on sap flow, the continuous canopy stomatal conductance (g_c) was calculated by Penman Monteith equation. An improved Jarvis-Stewart stomatal model was used for simulating the changes of g_c. The results showed that the environmental variables such as saturated vapor pressure deficit (VPD), air temperature (T_a), relative humidity (RH) and solar radiation (R_s) were significantly correlated with g_c of P. orientalis (P<0.01). The magnitude of the influence of those factors on g_c wereT_a>R_s>VPD>RH. In sunny days, the relationships between g_c and VPD and between g_c and T_a were characterized by a hysteresis loop, with the response path being different from the rising stage to descending stage. Moreover, those relationships showed different response patterns at different time. The JarvisStewart model performed better in simulating the responses of canopy stomatal conductance to environmental factors R_s,VPD, and T_a. Results from cross validation showed that optimal parameter calibration of this model explained 84.4% of the total variation.

Key words: orchard grass cultivation, high-throughput sequencing, diversity index, relative abundance, soil nutrient