Evaluation of water use of Caragana microphylla with the stem heat-balance method in Horqin Sandy Land, Inner Mongolia, China

Transpiration rates of a 15-year-old sand-fixation plantation of the leguminous shrub Caragana microphylla in the Horqin Sandy Land, northeast China, were measured by sap flow gauges throughout the summer of 2006. We extrapolated the measurements of water use by individual plants to determine the area-averaged transpiration (Ts) of the shrubland. The method used for the extrapolation assumes that the transpiration of a shrub was proportional to its leaf area. Similar results were found when comparing transpiration estimated with sap flow measurements to the actual evapotranspiration measured by the weighed lysimeter method, indicating that the scaling procedure can be used to provide reliable estimates of shrub transpiration. Daily sap flow rates and Ts were mainly controlled by photosynthetically active radiation (Q) and vapor pressure deficit (D), whereas soil moisture had more influence on monthly change in Ts. Maximum stand-level transpiration rates for C. microphylla ranged from 1.64 to 1.95 mm day−1, with an average value of 1.19 mm day−1. The seasonal (1 June to 31 August) total transpiration amounted to 109 mm, representing 66% of the incoming precipitation over this period. These results suggest that C. microphylla is highly effective at utilizing scarce water resources in semi-arid environments.