Research Unit Forest Dynamics, Swiss Federal Research Institute for Forest, Snow and Landscape Research WSL, 8903, Birmensdorf, Switzerland.
Institute of Terrestrial Ecosystems, ETH Zurich, 8092, Zurich, Switzerland.
New Phytol. 2022 Jan;233(1):194-206. doi: 10.1111/nph.17767. Epub 2021 Oct 15.
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.
未来干旱事件的强度和频率预计将会增加，这将对森林产生预期的不利影响。因此，有关树木在干旱期间和之后从不同土壤层吸收水分的动态信息至关重要。我们应用原位水同位素监测系统，以 2 小时的分辨率确定欧洲山毛榉的土壤和木质部水中的氧同位素组成，同时测量土壤含水量、蒸腾和树木水分亏缺。使用贝叶斯同位素混合模型，我们推断了来自四个不同土壤层的水对树木水分利用的相对和绝对贡献。在 2018 年干旱开始时，山毛榉从最上层 5 厘米的土壤层中吸收了超过 50%的水分，但随后减少了干燥表土中绝对水分的吸收量 84%。树木无法通过从更深的土壤层中额外吸收来定量补偿表土水分的有限可用性，这与细根的深度分布有关。在重新润湿后的 3 周内，从表土中吸收的水分恢复到干旱前的水平。这些吸收模式有助于解释山毛榉对干旱的敏感性及其在干旱释放后的高恢复潜力。
