Opportunities, challenges and pitfalls in characterizing plant water‐use strategies

Abstract

1. Classifying the diverse ways that plants respond to hydrologic stress into generalizable 'water-use strategies' has long been an eco-physiological research goal.While many schemes for describing water-use strategies have proven to be quite useful, they are also associated with uncertainties regarding their theoretical basis and their connection to plant carbon and water relations. In this review, we discuss the factors that shape plant water stress responses and assess the approaches used to classify a plant's water-use strategy, paying particular attention to the popular but controversial concept of a continuum from isohydry to anisohydry.2. A generalizable and predictive framework for assessing plant water-use strategies has been historically elusive, yet recent advances in plant physiology and hydraulics provide the field with a way past these obstacles. Specifically, we promote the idea that many metrics that quantify water-use strategies are highly dynamic and emergent from the interaction between plant traits and environmental conditions, and that this complexity has historically hindered the development of a generalizable water-use strategy framework.3. This idea is explored using a plant hydraulics model to identify: (a) distinct temporal phases in plant hydraulic regulation during drought that underpin dynamic water-use responses, and (b) how variation in both traits and environmental forcings can significantly alter common metrics used to characterize plant water-use strategies. This modelling exercise can bridge the divide between various conceptualizations of water-use strategies and provide targeted hypotheses to advance the understanding and quantification of plant water status regulation across spatial and temporal scales.4. Finally, we describe research frontiers that are necessary to improve the predictive capacity of the plant water-use strategy concept, including further investigation into the below-ground determinants of plant water relations, targeted data collection efforts and the potential to scale these concepts from individuals to whole regions.

Intra‐Specific Variability in Plant Hydraulic Parameters Inferred From Model Inversion of Sap Flux Data

“…Alternately, as σ increases, the plant moves toward anisohydric behavior, where it allows ψ x to decline (by regulating stomata less) with ψ s in order to prolong transpiration at the risk of hydraulic damage. Although there are confounding factors to the isohydricity concept (Feng et al., 2019; Novick et al., 2019), σ nevertheless provides useful insight into the inter‐ and intraspecific variability of plant water use strategies (Kannenberg et al., 2021). We fit the isohydricity index, σ , to each site and performed a species‐level comparison using a single factor ANOVA and pairwise t ‐tests using Tukey's HSD test to determine if σ values for each species differed and by how much.…”

Water Use Strategy of Riparian Conifers Varies with Tree Size and Depends on Coordination of Water Uptake Depth and Internal Tree Water Storage

“…The lack of significant correlation in between RWC and δ 2 H early July is potentially Differentials between the volumes of root water uptake and transpiration drive changes in tissue water content (Chitra-Tarak et al, 2018;Dralle et al, 2020;Nehemy et al, 2021). Reductions in tree stored water across the growing season have been described as the temporal integration of soil water stress occurring over weeks to months (Kannenberg et al, 2022). In contrast with this concept, we observed that RWC in higher elevation hemlock (experiencing substantially lower soil water availability) tended to have higher RWC from March through May and similar RWC to lower elevation trees from June through September (Fig.…”

“…How plant water use strategies are defined is an evolving concept that connects the dimensions of stomatal regulation in response to vapor pressure deficits, xylem resistance to embolism, trunk water storage, root access to subsurface water sources, foliar water uptake, and carbon investments during periods of stress (Carminati & Javaux, 2020;Kannenberg et al, 2022). Investment in deeper or denser rooting systems can provide trees access to more temporally stable water sources (Chitra-Tarak et al, 2018;Fan et al, 2017;Knighton et al, 2021;Mackay et al, 2020).…”

Temporal variation in stomatal sensitivity to vapour pressure deficit in western riparian forests

“…Similarly, leaf area changes via leaf abscission and regrowth (Dallstream & Piper, 2021; Filewod & Thomas, 2014) can change plant demand for water. Indeed, seasonal shifts in plant allometry can significantly impact hydraulic regulation, sometimes exceeding the influence of environmental variables (Kannenberg et al, 2021; Novick et al, 2019). Although allometric methods can be destructive and/or labour‐intensive, repeated measurements of plant allometry within a season can shed additional light on variable hydraulic regulation.…”

“…We also found species‐dependent changes in standardized stomatal sensitivity at the subannual scale, consistent with the findings of Wu et al (2021) at the inter‐annual scale. Future studies that incorporate multiple metrics of hydraulic regulation (reviewed in Feng et al, 2019) have the potential to reveal coordination, particularly between response‐ and trait‐based metrics (Kannenberg et al, 2021).…”