Drought reduces water uptake in beech from the drying topsoil, but no compensatory uptake occurs from deeper soil layers

Abstract

The intensity and frequency of droughts events are projected to increase in future with expected adverse effects for forests. Thus, information on the dynamics of tree water uptake from different soil layers during and after drought is crucial.We applied an in situ water isotopologue monitoring system to determine the oxygen isotope composition in soil and xylem water of European beech with a 2-h resolution together with measurements of soil water content, transpiration and tree water deficit. Using a Bayesian isotope mixing model, we inferred the relative and absolute contribution of water from four different soil layers to tree water use.Beech took up more than 50% of its water from the uppermost 5 cm soil layer at the beginning of the 2018 drought, but then reduced absolute water uptake from the drying topsoil by 84%. The trees were not able to quantitatively compensate for restricted topsoil water availability by additional uptake from deeper soil layers, which is related to the fine root depth distribution. Absolute water uptake from the topsoil was restored to pre-drought levels within 3 wk after rewetting.These uptake patterns help to explain both the drought sensitivity of beech and its high recovery potential after drought release.

Below Average Midsummer to Early Autumn Precipitation Evolved Into the Main Driver of Sudden Scots Pine Vitality Decline in the Swiss Rhône Valley

“…Tree damage caused by soil drought is largely dictated by the reached extreme of negative water potential and the amount of time spent at this extreme (Choat et al, 2018). Major rain events within a dry period, however, may result in a fast re-initiation of soil water uptake (Gessler et al, 2022) and thus recovery of important physiological tree functions (Skelton et al, 2017).…”

Precipitation fate and transport in a Mediterranean catchment through models calibrated on plant and stream water isotope data

“…There are limitations in comparing observations at one location within the Can Vila catchment with the presented catchment scale modeling but we believe that we can generally expect a disjunct isotopic signal between more and less mobile soil water in the highly structured soils in the Can Vila catchment. This assumption of widely occurring heterogenous flow is supported by numerous observations of mobile and bulk soil water isotope ratios in different soils in various climates (e.g., Brooks et al, 2010;Goldsmith et al, 2012;Hervé-Fernández et al, 2016;Sprenger et al, 2018;Zhao et al, 2018). Indeed, Beven and German (2013) suggested that the "distribution of preferential flow velocities" in soils could imply the importance of plot-to-hillslope-scale observations to catchment-scale processes.…”

“…Isotope measurements of the transpiration flux become more widely available due to lower costs and new technologies (Marshall et al, 2020;Volkmann et al, 2016) which allows sub-daily to daily xylem isotope analysis. However, such in-situ measurements have shown that xylem water isotope variation is by far less responsive than stream water isotopes (Gessler et al, 2022;Landgraf et al, 2022;Seeger and Weiler, 2021). Further, recent simulations with the EcH2O-iso model by Knighton et al (2020) indicated that mixing of water in plants could conceivably dampen root-uptake signals, undermining the insights that could be gained by high frequency xylem sampling.…”

Reply on RC1

“…Although soil moisture measurements across three soil layers are available at both sites, the deepest depth (ca. 30cm) cannot capture the entire soil water reservoir available for European beech which has been observed to have non-negligible amounts of fine roots below 30cm across different sites (Leuschner et al, 2004, Gessler et al, 2021.…”