Diurnal and seasonal variations of sap flow of Caragana korshinskii in the arid desert region of north-west China

The aim of this study was to obtain the diurnal and seasonal changes of trunk sap flow in desert-living Caragana korshinskii so as to understand its water requirement and ecological significance. The experiment was carried out with 15-year old Caragana korshinskii grown in north-west China under natural conditions. Heat pulse sensors based on the heat compensation theory were applied to measure the trunk sap flow, and soil moisture content at 0-300 cm layer, using tube-type time domain reflectometry (Tube-TDR). The solar radiation, the maximum and minimum air temperatures, relative humidity, wind speed, wind direction and precipitation were measured at a standard automatic weather station. The diurnal and seasonal variations of sap flow rate, the sap velocity at different positions in the trunk and the sap flow rate under different weather conditions were analysed. And the correlation between the sap flow rate and the meteorological factors was also analysed. Results showed that the trunk sap flow varied regularly in the diurnal term and the sap flow velocity decreased with the probe-inserted depth into the sapwood. Magnitude of sap flow changed considerably between sunny and rainy days. The order of the main meteorological factors affecting the sap flow rate of Caragana korshinskii shrubs were: vapour pressure deficit > solar radiation > air temperature > wind speed. The close correlation between daily sap flow rate and meteorological factors in the whole growing season can be used to estimate the transpiration of Caragana korshinskii. Copyright (c) 2007 John Wiley & Sons, Ltd.