Abstract
Abstract. Root water uptake (RWU), as an important process in the terrestrial water cycle, can help us to better understand the interactions in the soil–plant–atmosphere continuum. We conducted a field study monitoring soil moisture profiles in the rhizosphere of beech trees at two sites with different soil conditions. We present an algorithm to infer RWU from step-shaped, diurnal changes in soil moisture. While this approach is a feasible, easily implemented method for moderately moist and homogeneously textured soil conditions, limitations were identified during drier states and for more heterogeneous soil settings. A comparison with the time series of xylem sap velocity underlines that RWU and sap flow (SF) are complementary measures in the transpiration process. The high correlation between the SF time series of the two sites, but lower correlation between the RWU time series, suggests that soil characteristics affect RWU of the trees but not SF.
Highlights
Evapotranspiration (ET) is a key water and energy flux in ecosystems
Two summer thunderstorms damaged the loggers in the middle of the vegetation period, which caused an early end to the time series
The relatively high temporal resolution of the data, its continuous spatial distribution and its quality enable a perspective into the rhizosphere water dynamics, which is often conceptualised in models (Kuhlmann et al, 2012) but rarely measured
Summary
Evapotranspiration (ET) is a key water and energy flux in ecosystems. ET amounts globally to 60 % of total precipitation in terrestrial systems (Oki and Kanae, 2006), and transpiration is claimed to dominate the terrestrial water cycle (Jasechko et al, 2013), it remains one of the most challenging fluxes to observe and understand (Wulfmeyer et al, 2018; Renner et al, 2019). ET describes the release of water vapour into the atmosphere, driven by the saturation deficit of the atmosphere and influenced by soil and vegetation characteristics, which control soil water uptake and transport. It can be either limited by the radiative energy supply or by the terrestrial water supply. It is well known that the controls of transpiration are not static (Renner et al, 2016; Dubbert and Werner, 2019) Plants can adapt their water uptake and transport to their assimilation under different stressors (Schymanski et al, 2009; Lu et al, 2020). A series of approximations and assumptions is needed to con-
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