Differentiating refilling and transpiration from night-time sap flux based on time series modelling

Nocturnal Water Use Partitioning and Its Environmental and Stomatal Control Mechanism in Caragana korshinskii Kom in a Semi-Arid Region of Northern China

“…Our results indicate that, for C. korshinskii, T n accounted for 49.76% and 54.44% of nocturnal water use, as the mean values of R e :E n throughout the growing season were 50.24% and 45.56% in 2020 and 2021, respectively. The R e :E n values were much higher than the 20%-25% observed for oak and pine growing in a humid montane region [27], and were similar to S. superba planted in a humid region in the dry season [20]; however, they were slightly lower than that found in P. tomentosa approximately 61% planted in a semiarid region [22], and much lower than that found in P. euphratica approximately 80% growing in an extremely arid environment [2] and A. truncatum (>85%) planted in an urban environment [5]. The higher value of R e :E n in the water-limited environment indicated a greater reliance of plants on the water stored through stem refilling, which could help forests to maintain hydraulic support under higher transpiration demand [47,48].…”

“…Precisely identifying nocturnal transpiration and stem refilling components from continuous nocturnal water use will contribute to developing a better understanding of physiological responses to external environmental changes. Several methods have been proposed to distinguish nocturnal transpiration and stem refilling from nocturnal water use, such as the Penman-Monteith model [17], a flow model based on a resistance network [18], a time series model with one or more exogenous inputs [19,20] and a forecasted refilling method regarding determinationbased vapor pressure deficits (VPD) [13,21]. The forecasted refilling method, conducted by analyzing the slope of a daily sap flux curve, has been proven to be a simple and useful fraction method, and has been successfully applied on rainless nights in natural [1,2], planted [22,23] and urban forests [5].…”