Hydraulic Sensitivity and Stomatal Regulation of Two Desert Riparian Species. Issue 10 (12th October 2022)

• Record Type: Journal Article
• Authors: Bai, Yan; Liu, Yanlan; Kueppers, Lara M.; Li, Engui; Zhang, Cicheng; Yu, Kailiang; Yang, Xiaofan; Li, Xiaoyan
• Is Part Of: Journal of geophysical research. Volume 127:Issue 10(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-10-12
• Subjects: isohydricity -- hydraulic traits -- groundwater -- water use -- stomatal conductance; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2022JG006971
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: Characterizing plant response to water stresses is among the keys to understanding ecosystem functions. Despite increasing recognition of plant hydraulic and stomatal dynamics not captured by isohydricity, defined as the sensitivity of leaf water potential Ψ l to soil water potential, it remains unclear which plant traits are critical to improved representation of plant hydraulic and stomatal dynamics beyond isohydricity, especially in dryland ecosystems. Here, we examine eco‐physiological responses of two typical desert riparian species, Populus euphratica and Tamarix ramosissima, to hydro‐meteorological variations. Based on measured hydraulic traits, variations of Ψ l, leaf gas exchange, groundwater table, and soil moisture across vertical profiles, we investigated how subsurface hydraulic conditions control plant hydraulic sensitivity and stomatal regulation. We found both species exhibited anisohydric behaviors, which, however, were attributed to drying soil at different depths because of root distributions. The similar anisohydric behaviors also led to distinct stomatal regulation, due to the impact of atmospheric dryness decoupled from soil moisture and different sensitivities of stomatal conductance ( g s ) to Ψ l . The latter was found to be dynamic throughout the growing season, which dominated the seasonal variation of g s and thus should not be neglected. The results suggest similar anisohydric behaviors could imply diverging hydraulic behaviors as the evaporate demand and flow regime change. Root morphological trait and stomatal sensitivity to Ψ l are identified as keys to characterize responses to water stresses in desert riparian ecosystems. Our findings highlight that improved measurements and representations of these traits could contribute to better assessments of dryland ecosystem functions. Plain Language Summary: Many ecosystem functions, including plant water uptake, carbon sink, and tree death, directly depend on how plants respond to water stresses. Recent studies have used simplified metrics to quantify how sensitive leaf water potential is to drying soils, which, however, neglects important aspects of plant hydraulic and stomatal responses. Notably, which plant traits control these neglected responses remain unclear, especially in dryland ecosystems. Based on measurements of environmental conditions, physiological dynamics, and plant traits, we find two desert riparian ecosystems show similar hydraulic sensitivities as the soil dries, but are caused by dry soils in different depths and lead to distinct stomatal behaviors. These distinctions originate from different root vertical distributions and stomatal sensitivities to leaf water potential. Our results suggest that plants with similar hydraulic sensitivity to drying soil based on traditional measure could have divergent behaviors. Plants with more roots in the shallow layer and more hydraulicly sensitive stomata are expected to be more vulnerable to projected hotter droughts, which could dry up the upper soil and suppress stomata opening faster. Our findings highlight the need to better quantify root and stomata properties for improved prediction of water recourses and plant vulnerability in dryland ecosystems under future climate. Key Points: Similar anisohydric behaviors are caused by different subsurface water stresses and lead to distinct stomatal behaviors Different controls of hydrological stresses originate from site‐specific root morphological traits Better quantification of root traits and dynamic stomatal sensitivity contribute to improved understanding of plant stress‐responses