Abstract:

The sap flows(F_s) in taproot of Caragana korshinskii were measured continually withthermal dissipation probe（TDP）technique from April to October in 2008, and the environmental factors were recorded synchronously. The data of 30 sunny days were selected for analysis. The results showed that the forms ofF_s exhibits a typical normal distribution with wide peak, which could be divided into 4 phaseobviously, reflecting driven effects of meteorological factors and regulation effects of stomatal behavior. TheF_s was driven by multiple factors jointly. The potential evapotranspiration（ET₀）wasclosely correlated to F_s so as to be a comprehensive and compounded environmental variable. Thecoupling relationship between F_s and main environment factors varied diurnally. F_s had a liner relationship with solar radiation and ET₀ at initiating and increasing stage of the flow after sunrise, which suggested that the solar radiation would be the driving mechanism to F_s and activation effects of photosynthesis. F_s showed a Sigmoidal-Hill function relationship with solar radiation and ET₀ at the decreasing stage after the peak. The F_s relationships with vapour pressure deficit（VPD）was contrary to that with solar radiation and ET₀ ,which implied that VPD could trigger stomatal regulation and control over-transpiration. F_s varied with main environment factors nearly simultaneously and no obvious time lags were found. Nocturnal sap flows were measured in many days of the growth season, and the average flow accounted for 3.83% of the total daily sap flows. The results approved the validation and superiority of the TDP technique for measuring sap flow of the whole tree in taproot of the shrubs.

Key words: thermal dissipation probe(TDP), Caragana korshinskii, sap flows in taproot, potential evapotranspiration(ET₀), environmental factors