Increasing temperature and vapour pressure deficit lead to hydraulic damages in the absence of soil drought

Abstract

Temperature (T) and vapour pressure deficit (VPD) are important drivers of plant hydraulic conductivity, growth, mortality, and ecosystem productivity, independently of soil water availability. Our goal was to disentangle the effects of T and VPD on plant hydraulic responses. Young trees of Fagus sylvatica L., Quercus pubescens Willd. and Quercus ilex L. were exposed to a cross-combination of a T and VPD manipulation under unlimited soil water availability. Stem hydraulic conductivity and leaf-level hydraulic traits (e.g., gas exchange and osmotic adjustment) were tracked over a full growing season. Significant loss of xylem conductive area (PLA) was found in F. sylvatica and Q. pubescens due to rising VPD and T, but not in Q. ilex. Increasing T aggravated the effects of high VPD in F. sylvatica only. PLA was driven by maximum hydraulic conductivity and minimum leaf conductance, suggesting that high transpiration and water loss after stomatal closure contributed to plant hydraulic stress. This study shows for the first time that rising VPD and T lead to losses of stem conductivity even when soil water is not limiting, highlighting their rising importance in plant mortality mechanisms in the future.

A herbaceous species provides insights into drought-driven plant adaptation

“…The below-ground component is another fundamental and understudied part of this continuum, with both woody and herbaceous species found to be sensitive to drought-driven declines in root hydraulic conductance ( K r ; Bourbia et al , 2021 ), and K r found to drive stomatal closure in olive ( Rodriguez-Dominguez and Brodribb, 2020 ). Air temperature and water content are also crucial during drought, with recent research finding that high temperature and high vapour pressure deficit can induce drought damage even in the absence of soil drought ( Schönbeck et al , 2022 ). Interdisciplinary research, such as the study by Thonglim et al (2023) , and an integrative, holistic perspective across disciplines are both vital in our efforts to characterize and accurately interpret the complex nature of drought tolerance and resistance across plant species.…”

How the interactions between atmospheric and soil drought affect the functionality of plant hydraulics

“…The recent paper by Schönbeck et al ( 2022 ) investigated the effect of rising VPD and temperature on plant hydraulics. The authors observed that VPD and temperature led to losses in stem hydraulic conductivity independently from soil drought.…”

“…Significant losses in stem xylem hydraulic conductivity, up to about 75% in F. sylvatica and Q. pubescens , were observed. The authors concluded that ‘VPD and temperature can cause major hydraulic dysfunctions’ (Schönbeck et al, 2022 ).…”

“…E was normalized by leaf area. The data in subplots (a−g) are from Schönbeck et al ( 2022 ) while those in subplots (g−i) are from Cai et al ( 2022 ). L, M, and H refer to low, middle, and high vapor pressure deficit.…”

“…Schönbeck et al ( 2022 ) highlighted that the observations of xylem hydraulic damage were found ‘without soil drought’. Indeed, in their study there was no decline in soil−plant hydraulic conductance, and presumably neither xylem embolism nor partial soil drying limited transpiration.…”