| Summary: | The traditional heat balance method for measuring plant sap flow (SF) becomes troublesome and uneconomic for multibranched shrub species if all their stems are used for the measurement. The objectives of this study were to explore specific relationships between stem-scale SF and plant morphological traits and then to scale up SF measurements from the stem scale to the individual scale for <i>Caragana korshinskii</i> Kom., a dominant shrub species on the Chinese Loess Plateau. Sap flow was measured for twenty-one stems from three representative individuals from July to September 2018 during the rainy season. The results indicated that the stem-scale SF in <i>C. korshinskii</i> presented a positive linear correlation with the stem base diameter (SBD), stem length (SL), primary branch numbers in the stem (PBN), and estimated stem biomass (W). The SBD-based statistical models performed well in estimating the stem-scale SF, with an <i>R</i><sup>2</sup> value of 0.9726 and root mean squared error (RMSE) of 2.5389 g h<sup>−1</sup>. Over the canopy projection area, the individual-scale transpiration flows for the three selected <i>C. korshinskii</i> were 1.91, 1.10, and 1.59 mm·d<sup>−1</sup>. In addition, stem-scale SF was positively and linearly correlated with air temperature, photosynthetically active radiation, vapor pressure deficit, reference crop evapotranspiration, and variable transpiration. This study sheds light on morphological and meteorological influences on stem-scale SF and has made contributes to the accurate and rapid estimation of the plant sap flow from easily available morphological traits for multibranched shrub species in semiarid regions. Limitations, however, may exist for the established model when it is used to estimate SF of <i>C. korshinskii</i> during the water-limited dry season. Our study deserves further exploration of a more general model to have a better estimation of SF for <i>C. korshinskii</i> in both dry and rainy seasons.
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