Daytime stomatal regulation in mature temperate trees prioritizes stem rehydration at night

Abstract

Trees remain sufficiently hydrated during drought by closing stomata and reducing canopy conductance (G c ) in response to variations in atmospheric water demand and soil water availability. Thresholds that control the reduction of G c are proposed to optimize hydraulic safety against carbon assimilation efficiency. However, the link between G c and the ability of stem tissues to rehydrate at night remains unclear.We investigated whether species-specific G c responses aim to prevent branch embolisms, or enable night-time stem rehydration, which is critical for turgor-dependent growth. For this, we used a unique combination of concurrent dendrometer, sap flow and leaf water potential measurements and collected branch-vulnerability curves of six common European tree species.Species-specific G c reduction was weakly related to the water potentials at which 50% of branch xylem conductivity is lost (P 50 ). Instead, we found a stronger relationship with stem rehydration. Species with a stronger G c control were less effective at refilling stem-water storage as the soil dries, which appeared related to their xylem architecture.Our findings highlight the importance of stem rehydration for water-use regulation in mature trees, which likely relates to the maintenance of adequate stem turgor. We thus conclude that stem rehydration must complement the widely accepted safety-efficiency stomatal control paradigm.

High vapour pressure deficit enhances turgor limitation of stem growth in an Asian tropical rainforest tree

“…Tree-internal water fluxes, which steer turgor variability in growing tissue, are largely regulated by stomatal control (Potkay & Feng, 2023; see also Dewar et al, 2022;Peters et al, 2023).…”

“…Tree‐internal water fluxes, which steer turgor variability in growing tissue, are largely regulated by stomatal control (Potkay & Feng, 2023; see also Dewar et al, 2022; Peters et al, 2023). Stomatal closure is a key mechanism for trees to balance the fixation of atmospheric CO 2 with the loss of water (Buckley, 2019; Edwards et al, 1998).…”

Unpacking the point of no return under drought in poplar: insight from stem diameter variation

“…4). At the beginning of the drought, at higher water potentials, trees were able to replenish their tissues at night (Pfautsch et al, 2015;Zweifel et al, 2021;Peters et al, 2023), the PLD we scored was thus null under these conditions. As the drought progressed and the water potential decreased, the tissues were no longer able to rehydrate during the night, which led to a continuous increase in PLD.…”

Beyond source and sink control – toward an integrated approach to understand the carbon balance in plants

“…That Potkay-Feng model offers a smart explanation for the overall plant coordination of source and sink activity via stomatal responses by targeting growth optimization on the mid-and long term rather than primary production in the short term. Peters et al (2023b) underscored this argument by showing that stomatal regulation is not only driven by attempts to avoid embolism in the water supply system but is additionally or even primarily regulated to maintain daytime dehydration at a moderate level. Only then, a tree can be replenished during the night, and thus, the water potential comes into a range that allows stem growth (Zweifel et al, 2021).…”

“…Peters et al . (2023b) underscored this argument by showing that stomatal regulation is not only driven by attempts to avoid embolism in the water supply system but is additionally or even primarily regulated to maintain daytime dehydration at a moderate level. Only then, a tree can be replenished during the night, and thus, the water potential comes into a range that allows stem growth (Zweifel et al ., 2021).…”