Interannual variability of ecosystem iso/anisohydry is regulated by environmental dryness

Abstract

Summary ●Plants are characterized by the iso/anisohydry continuum depending on how they regulate leaf water potential (ΨL). However, how iso/anisohydry changes over time in response to year‐to‐year variations in environmental dryness and how such responses vary across different regions remains poorly characterized. ●We investigated how dryness, represented by aridity index, affects the interannual variability of ecosystem iso/anisohydry at the regional scale, estimated using satellite microwave vegetation optical depth (VOD) observations. This ecosystem‐level analysis was further complemented with published field observations of species‐level ΨL. ●We found different behaviors in the directionality and sensitivity of isohydricity (σ) with respect to the interannual variation of dryness in different ecosystems. These behaviors can largely be differentiated by the average dryness of the ecosystem itself: in mesic ecosystems, σ decreases in drier years with a higher sensitivity to dryness; in xeric ecosystems, σ increases in drier years with a lower sensitivity to dryness. These results were supported by the species‐level synthesis. ●Our study suggests that how plants adjust their water use across years – as revealed by their interannual variability in isohydricity – depends on the dryness of plants’ living environment. This finding advances our understanding of plant responses to drought at regional scales.

Global ecosystem-scale plant hydraulic traits retrieved using model–data fusion

“…As a result of their effect on the surface energy balance, plant hydraulic traits also impact the magnitude of land-atmosphere feedbacks (Anderegg et al, 2019). In dry tropical forests, leaf water potential -which is directly influenced by hydraulic traits -has also been shown to affect leaf phenology (Xu et al, 2016). As a result, it has been increasingly recognized that plant hydraulic traits are important for mediating ecosystem drought response and hydroclimatic feedbacks at regional to global scales (Choat et al, 2012;Anderegg, 2015;Choat et al, 2018;Hartmann et al, 2018).…”

“…At a stand scale, this plant physiological metric has been used to explain photosynthesis variations (Roman et al, 2015) and drought mortality risk (McDowell et al, 2008) across species. At a global scale, remote-sensing-derived isohydricity patterns have been used to explain photosynthesis sensitivity to vapor pressure deficit and soil moisture in North American grasslands and the Amazon (Giardina et al, 2018), to explore the interannual variability in isohydricity (Wu et al, 2020) and to explain the relationship between drought resistance and resilience in gymnosperms (Li et al, 2020). However, because isohydricity is an emergent rather than intrinsic property, it is subject to change with en-vironmental conditions (Hochberg et al, 2018;Novick et al, 2019;Feng et al, 2019;Mrad et al, 2019).…”

“…From a modeling perspective, as plant hydraulics has been increasingly recognized as a central link connecting hydroclimatic processes and ecosystem ecology (Sack et al, 2016;McDowell et al, 2019), land surface and dynamic vegetation models that explicitly incorporate plant hydraulics are becoming more common (e.g., Xu et al, 2016;Christoffersen et al, 2016;Kennedy et al, 2019;De Kauwe et al, 2020;Eller et al, 2020). However, explicit plant hydraulic representation also requires parameterization choices for the associated plant hydraulic traits.…”

Towards a statistically robust determination of minimum water potential and hydraulic risk in plants

“…This type of analysis should be facilitated by increased availability of environmental drivers and detailed soil and plant water content measures from remote sensing (cf. Wu et al ., 2021).…”

Representation of Plant Hydraulics in the Noah‐MP Land Surface Model: Model Development and Multiscale Evaluation

“…At the shoot-level, plants regulate stomatal conductance during water stress across a continuum from relatively isohydric regulation in which rapid stomatal closure is associated with a smaller range of experienced leaf water potential, to relatively anisohydric regulation with higher stomatal conductance and a larger range of experienced leaf water potential. Most plants operate along a range of intermediate strategies between these two extremes (Blackman, 2018;McDowell et al, 2008;Skelton et al, 2015;Zhu et al, 2018), and relative anisohydricity can vary seasonally and interannually (Hochberg et al, 2018;Wu et al, 2020). At the stem level, plants differ in their xylem architecture, including ring-porous, diffuse-porous, and tracheid-based types (Matheny et al, 2017;Oren et al, 1999).…”