Aridity‐dependent sequence of water potentials for stomatal closure and hydraulic dysfunctions in woody plants

Abstract

The sequence of physiological events during drought strongly impacts plants' overall performance. Here, we synthesized the global data of stomatal and hydraulic traits in leaves and stems of 202 woody species to evaluate variations in the water potentials for key physiological events and their sequence along the climatic gradient. We found that the seasonal minimum water potential, turgor loss point, stomatal closure point, and leaf and stem xylem vulnerability to embolism were intercorrelated and decreased with aridity, indicating that water stress drives trait co‐selection. In xeric regions, the seasonal minimum water potential occurred at lower water potential than turgor loss point, and the subsequent stomatal closure delayed embolism formation. In mesic regions, however, the seasonal minimum water potential did not pose a threat to the physiological functions, and stomatal closure occurred even at slightly more negative water potential than embolism. Our study demonstrates that the sequence of water potentials for physiological dysfunctions of woody plants varies with aridity, that is, xeric species adopt a more conservative sequence to prevent severe tissue damage through tighter stomatal regulation (isohydric strategy) and higher embolism resistance, while mesic species adopt a riskier sequence via looser stomatal regulation (anisohydric strategy) to maximize carbon uptake at the cost of hydraulic safety. Integrating both aridity‐dependent sequence of water potentials for physiological dysfunctions and gap between these key traits into the hydraulic framework of process‐based vegetation models would improve the prediction of woody plants' responses to drought under global climate change.

Regulation of NDVI and ET negative responses to increased atmospheric vapor pressure deficit by water availability in global drylands

“…These observations have been supported by a recent study conducted in seasonal dry subtropical forests (Chen et al, 2021). This could be attributable to Xeric species adopting a more conservative sequence to prevent severe tissue damage through tighter stomatal regulation (isohydric strategy) and higher embolism resistance (Jin et al, 2023), especially for the sunnier and drier seasons .…”

Vegetation and Evapotranspiration Responses to Increased Atmospheric Vapor Pressure Deficit across the Global Forest

“…This negative response of plant photosynthesis and transpiration to an increasing VPD has always been observed in water-limited regions [4,5]. This is because, in these regions, xeric species tend to adopt a more conservative sequence to prevent severe tissue damage through tighter stomatal regulation and higher resistance to embolism [32]. In contrast, the LAI and ET can resist the atmospheric dryness caused by an increasing VPD across the mostly forest regions, especially for the water-rich regions.…”

“…Although annual precipitation in most boreal forest regions is always less than 500 mm, they are not water-limited due to the high soil water-holding capacity of high soil organic matter [33] and low water loss under thermal constraint. Mesic species adopt a riskier sequence through looser stomatal regulation to maximize carbon uptake at the expense of hydraulic safety [32]. Plant root systems could partly determine how a certain soil water availability is translated into leaf water potential, which is strongly correlated with stomatal activity [34].Forests can extract deeper soil water through vigorous root systems and allow them to maintain higher leaf water potential and stomatal openness under dryness stress (such as under a VPD) [7,19].…”

Warming-induced vapor pressure deficit suppression of vegetation growth diminished in northern peatlands

“…Even if atmospheric water stress occurs as warming-induced VPD increases, the stress may be below the threshold that leads to stomatal closure, as evidenced by the neutral response of Gc, Et, and GPP to increasing VPD. In this wet soil-air environment, plants adopt an "open" water-use strategy in response to water stress, maximizing carbon uptake by relaxing stomatal regulation 24,29 . Although an "open" water-use strategy may sacrifice hydraulic security, plants in water-rich environments would benefit more from keeping their stomata open to take up carbon than from conserving water 29,41 .…”

“…A moist and cold environment combined with high moss cover may produce sufficient atmospheric moisture to meet the increasing water demand caused by increasing VPD in northern peatlands 18 , potentially relieving atmospheric dryness 27,28 . In this wet soil-air environment, plants may adopt an "open" water-use strategy in response to water stress by relaxing stomatal regulation to maximize carbon uptake at the cost of hydraulic risk 29 .…”