Iso/Anisohydry: Still a Useful Concept

Ratzmann, Gregor; Meinzer, Frederick C.; Tietjen, Britta

doi:10.1016/j.tplants.2019.01.001

Cited by 24 publications

(17 citation statements)

References 11 publications

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“…Interestingly, the narrow range of hydroscape area in our study (about 22% of the estimated global hydroscape area range) captured a relatively wider range of wood density variation (56%) along the global plant economic spectrum (Reich, 2014), demonstrating that the ability to identify small variations in species' degree of isohydry plays an important role in identifying and characterising species' resource and growth strategies within the plant community we studied. Here we provide evidence to support the notion that definitions of iso/anisohydry should be referenced to species' relative positions along a continuum rather than a dichotomous classification (Meinzer et al , 2016; Ratzmann et al , 2019). Our results further suggest that within a given environment even a narrow range of species' degree of iso/anisohydry could have important ecological implications, especially in terms of species' overall resource acquisition strategies.…”

Section: Discussionsupporting

confidence: 65%

“…Under current global change scenarios, the adaptability of different species to drought will determine the structure and function of plant communities (Thuiller et al , 2008; Tylianakis et al , 2008; Anderegg et al , 2012). A continuum of isohydric to anisohydric behaviour provides a framework for characterising whole‐plant, species‐specific differences in the stringency of stomatal control of transpiration and thus leaf water potential during drought (Klein, 2014; Martínez‐Vilalta et al , 2014; Meinzer et al , 2016; Ratzmann et al , 2019). Generally, isohydric species maintain a relatively constant midday minimum leaf water potential (Ψ md ) despite changes in soil water potential (Ψ S ), whereas Ψ md of anisohydric species covaries more strongly with Ψ S (Meinzer et al , 2016, 2017; Hochberg et al , 2018).…”

Section: Introductionmentioning

confidence: 99%

“…It is difficult to scale such species‐specific iso/anisohydric behaviour to the ecosystem scale (Konings & Gentine, 2017), as coexisting plants can exhibit different hydraulic behaviour and degrees of isohydry (Quero et al , 2011; Roman et al , 2015). However, the relative degree of iso/anisohydry could reflect interspecific or intraspecific differences in the ability to adjust to different environments when the concept is applied either to a single species across environmental gradients or different species under similar environmental conditions (Ratzmann et al , 2019; Novick et al , 2019). Nevertheless, important knowledge gaps persist concerning the broad applicability of this framework and how plant functional traits are integrated to yield a given degree of iso/anisohydry.…”

Section: Introductionmentioning

confidence: 99%

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Below‐ground determinants and ecological implications of shrub species' degree of isohydry in subtropical pine plantations

et al. 2020

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The degree of plant iso/anisohydry is a popular framework for characterising species-specific drought responses. However, we know little about associations between below-ground and above-ground hydraulic traits as well as the broader ecological implications of this framework.For 24 understory shrub species in seasonally dry subtropical coniferous plantations, we investigated contributions of the degree of isohydry to species' resource economy strategies, abundance, and importance value, and quantified the hydraulic conductance (K h ) of aboveground and below-ground organs, magnitude of deep water acquisition (WA deep ), shallow absorptive root traits (diameter, specific root length, tissue density), and resource-use efficiencies (A max , maximum photosynthesis rate; PNUE, photosynthetic nitrogen-use efficiency).The extreme isohydric understory species had lower wood density (a proxy for higher growth rates) because their higher WA deep and whole-plant K h allowed higher A max and PNUE, and thus did not necessarily show lower abundance and importance values. Although species' K h was coordinated with their water foraging capacity in shallow soil, the more acquisitive deep roots were more crucial than shallow roots in shaping species' extreme isohydric behaviour.Our results provide new insights into the mechanisms through which below-ground hydraulic traits, especially those of deep roots, determine species' degree of isohydry and economic strategies.

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Section: Discussionsupporting

confidence: 65%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Below‐ground determinants and ecological implications of shrub species' degree of isohydry in subtropical pine plantations

et al. 2020

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“…The conceptual framework in Fig. 8 can be confounded by very different environmental boundaries between the Phase I, II and III regimes of the Ψ MD –Ψ PD or VOD midday –VOD midnight curves in xeric and mesic ecosystems where all phases occur in a single year; other factors may also affect the trajectory in addition to aridity, such as hydraulic characteristics (Martínez‐Vilalta et al ., 2014), root traits (Matheny et al ., 2017), and soil and topography (Feng et al ., 2019; Ratzmann et al ., 2019a). We therefore expect our results to be borne out on average, but not universally, among sites.…”

Section: Discussionmentioning

confidence: 99%

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

Guan

et al. 2020

New Phytologist

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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.

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“…One area of interest is the possibility to use remote sensing to detect isohydric and anisohydric behavior, which is concept related to leaf water potential (Ψ L ) [95]. Leaf water content can be retrieved from optical (between 800 nm and 2500 nm) and microwave radiation [10].…”

Section: Physiological Biochemical Morphological and Remote Sensing Responses Under Water Stressmentioning

confidence: 99%

Hyperspectral and Thermal Sensing of Stomatal Conductance, Transpiration, and Photosynthesis for Soybean and Maize under Drought

et al. 2020

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During water stress, crops undertake adjustments in functional, structural, and biochemical traits. Hyperspectral data and machine learning techniques (PLS-R) can be used to assess water stress responses in plant physiology. In this study, we investigated the potential of hyperspectral optical (VNIR) measurements supplemented with thermal remote sensing and canopy height (hc) to detect changes in leaf physiology of soybean (C3) and maize (C4) plants under three levels of soil moisture in controlled environmental conditions. We measured canopy evapotranspiration (ET), leaf transpiration (Tr), leaf stomatal conductance (gs), leaf photosynthesis (A), leaf chlorophyll content and morphological properties (hc and LAI), as well as vegetation cover reflectance and radiometric temperature (TL,Rad). Our results showed that water stress caused significant ET decreases in both crops. This reduction was linked to tighter stomatal control for soybean plants, whereas LAI changes were the primary control on maize ET. Spectral vegetation indices (VIs) and TL,Rad were able to track these different responses to drought, but only after controlling for confounding changes in phenology. PLS-R modeling of gs, Tr, and A using hyperspectral data was more accurate when pooling data from both crops together rather than individually. Nonetheless, separated PLS-R crop models are useful to identify the most relevant variables in each crop such as TL,Rad for soybean and hc for maize under our experimental conditions. Interestingly, the most important spectral bands sensitive to drought, derived from PLS-R analysis, were not exactly centered at the same wavelengths of the studied VIs sensitive to drought, highlighting the benefit of having contiguous narrow spectral bands to predict leaf physiology and suggesting different wavelength combinations based on crop type. Our results are only a first but a promising step towards larger scale remote sensing applications (e.g., airborne and satellite). PLS-R estimates of leaf physiology could help to parameterize canopy level GPP or ET models and to identify different photosynthetic paths or the degree of stomatal closure in response to drought.

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Iso/Anisohydry: Still a Useful Concept

Cited by 24 publications

References 11 publications

Below‐ground determinants and ecological implications of shrub species' degree of isohydry in subtropical pine plantations

Below‐ground determinants and ecological implications of shrub species' degree of isohydry in subtropical pine plantations

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

Hyperspectral and Thermal Sensing of Stomatal Conductance, Transpiration, and Photosynthesis for Soybean and Maize under Drought

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