Characteristics and simulation of the canopy conductance of Hippophae rhamnoides in Qaidam Region of northwestern China

The aim of this study was to explain the response of canopy conductance of sea buckthorn (Hippophae rhamnoides ) to different environmental conditions so as to evaluate the feasibility of application of Jarvis model in sea buckthorn at the canopy scale. By using Granier's thermal dissipation probe, the sap flow of sea buckthorn in Qaidam Basin in Qinghai Province,northwestern China was continuously measured,and as well,the environmental factors such as incoming solar radiation intensity (Rs), air temperature (T), relative humidity (RH), wind speed (u) and rainfall were synchronically measured.Based on sap flow, canopy conductance (gc) was continuously simulated by back-calculated Penman-Monteith model. By analysis of gc of sea buckthorn, Jarvis stomatal model was simulated and analyzed with cross-validation. The results indicated that the diurnal variation in canopy conductance of sea buckthorn showed a single-peaked curve. There was a negative logarithm relationship between canopy conductance and vapor pressure deficit (VPD) under different radiation conditions. And the canopy conductance had a positive relationship with solar radiation intensity. The three variables, VPD, T and Rs, explained 81% of the variation in conductance in Jarvis-type mode, with the lowest average relative error of only 11.01%. And the degree of the environmental factors affecting the simulation accuracy of the model is ranked as VPD>Rs>T.