Physiological recovery of tree water relations upon drought release—response of mature beech and spruce after five years of recurrent summer drought. (22nd November 2022)

• Record Type: Journal Article
• Authors: Hesse, Benjamin D; Gebhardt, Timo; Hafner, Benjamin D; Hikino, Kyohsuke; Reitsam, Anna; Gigl, Michael; Dawid, Corinna; Häberle, Karl-Heinz; Grams, Thorsten E E
• Editors: Tognetti, Roberto
• Is Part Of: Tree physiology. Volume 43:Number 4(2023)
• Page Start: 522
• Page End: 538
• Publication Date: 2022-11-22
• Subjects: climate change -- drought stress release -- forest ecosystems -- osmotic potential -- resilience -- soil water content -- stomatal conductance -- water potential -- xylem sap flow density; Trees -- Physiology -- Periodicals; 582.16
• DOI: 10.1093/treephys/tpac135
• Languages: English
• ISSNs: 0829-318X

Abstract

Abstract: As climate change progresses, the frequency and duration of drought stress events are increasing. While the mechanisms of drought acclimation of trees has received considerable attention in recent years, the recovery processes remain critically understudied. We used a unique throughfall exclusion experiment in a mature temperate mixed forest consisting of the more isohydric Norway spruce and more anisohydric European beech, to study the recovery and resilience after drought release. We hypothesized that pre-dawn water potential (ΨPD ) of both species will increase within 1 day after watering, while the recovery of stomatal conductance ( g s ) and the reversal of osmoregulation will be significantly delayed in the more isohydric spruce. Furthermore, we hypothesized that the xylem sap flow density ( u daily ) will not fully recover within the growing season due to the strong drought impact. After 5 years of summer drought, trees showed significantly reduced ΨPD, u daily and increased osmoregulation in leaves, but only isohydric spruce displayed increased leaf abscisic acid concentrations. In line with our hypothesis, ΨPD and g s recovered within 1 day in beech. Conversely, isohydric spruce showed delayed increases in ΨPD and g s . The delay in recovery of spruce was partially related to the replenishment of the stem water reservoir, as indicated by the missing response of u daily at the crown base compared with DBH level upon watering. However, u daily fully recovered only in the next growing season for beech and was still reduced in spruce. Nevertheless, in both species, osmotic acclimations of leaves were reversed within several weeks. While both species displayed full resilience to drought stress in water-related physiology, the recovery time was in several cases, e.g., u daily, ΨPD and g s, shorter for beech than for spruce. With future increases in the frequency of drought events under ongoing climate change, tree species that recover more quickly will be favored.