Stomatal Function across Temporal and Spatial Scales: Deep-Time Trends, Land-Atmosphere Coupling and Global Models

Increasing vapor pressure deficit (VPD) increases atmospheric demand for water. While increased evapotranspiration (ET) in response to increased atmospheric demand seems intuitive, plants are capable of reducing ET in response to increased VPD by closing their stomata. We examine which effect dominates the response to increasing VPD: atmospheric demand and increases in ET or plant response (stomata closure) and decreases in ET. We use Penman‐Monteith, combined with semiempirical optimal stomatal regulation theory and underlying water use efficiency, to develop a theoretical framework for assessing ET response to VPD. The theory suggests that depending on the environment and plant characteristics, ET response to increasing VPD can vary from strongly decreasing to increasing, highlighting the diversity of plant water regulation strategies. The ET response varies due to (1) climate, with tropical and temperate climates more likely to exhibit a positive ET response to increasing VPD than boreal and arctic climates; (2) photosynthesis strategy, with C3 plants more likely to exhibit a positive ET response than C4 plants; and (3) plant type, with crops more likely to exhibit a positive ET response, and shrubs and gymniosperm trees more likely to exhibit a negative ET response. These results, derived from previous literature connecting plant parameters to plant and climate characteristics, highlight the utility of our simplified framework for understanding complex land‐atmosphere systems in terms of idealized scenarios in which ET responds to VPD only. This response is otherwise challenging to assess in an environment where many processes coevolve together.

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“…For example, C3 crops have both the highest g 1 value in Franks et al. () and the highest uWUE value in Zhou et al. ().…”

Section: Resultsmentioning

confidence: 97%

When Does Vapor Pressure Deficit Drive or Reduce Evapotranspiration?

Massmann

Gentine

Lin

2019

J Adv Model Earth Syst

158

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“…Night-time sap-flow and transpiration are greatest in species with rapid growth, high concentrations of leaf nitrogen and lower shade tolerances (Marks and Lechowicz 2007). Comprehensive modelling of all these processes and relationships remains a challenge (Buckley 2017;Franks et al 2017;Matthews et al 2017).…”

Section: Vapourmentioning

confidence: 99%

“…For example, we know that the flow of water vapour from the land surface depends on many factors, not all of which are fully characterised or represented in models (and the many simulations, such as the IPCC scenarios, that depend on these). Such effects may oppose each other, making the outcome unclear, for example, we know that forest loss and reduced stomatal opening associated with increasing carbon dioxide is likely to reduce vapour transpired to the atmosphere (Spracklen et al 2012;Sheil 2014;Franks et al 2017), but increasing leaf area observed in many regions may also boost transpiration (Zhang et al 2015).…”

Section: Water Security and The Imperative Of Improved Understandingmentioning

confidence: 99%

Forests, atmospheric water and an uncertain future: the new biology of the global water cycle

Sheil

2018

For. Ecosyst.

127

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Theory and evidence indicate that trees and other vegetation influence the atmospheric water-cycle in various ways. These influences are more important, more complex, and more poorly characterised than is widely realised. While there is little doubt that changes in tree cover will impact the water-cycle, the wider consequences remain difficult to predict as the underlying relationships and processes remain poorly characterised. Nonetheless, as forests are vulnerable to human activities, these linked aspects of the water-cycle are also at risk and the potential consequences of large scale forest loss are severe. Here, for non-specialist readers, I review our knowledge of the links between vegetation-cover and climate with a focus on forests and rain (precipitation). I highlight advances, uncertainties and research opportunities. There are significant shortcomings in our understanding of the atmospheric hydrological cycle and of its representation in climate models. A better understanding of the role of vegetation and tree-cover will reduce some of these shortcomings. I outline and illustrate various research themes where these advances may be found. These themes include the biology of evaporation, aerosols and atmospheric motion, as well as the processes that determine monsoons and diurnal precipitation cycles. A novel theory-the 'biotic pump'-suggests that evaporation and condensation can exert a major influence over atmospheric dynamics. This theory explains how high rainfall can be maintained within those continental land-masses that are sufficiently forested. Feedbacks within many of these processes can result in non-linear behaviours and the potential for dramatic changes as a result of forest loss (or gain): for example, switching from a wet to a dry local climate (or visa-versa). Much remains unknown and multiple research disciplines are needed to address this: forest scientists and other biologists have a major role to play. New ideas, methods and data offer opportunities to improve understanding. Expect surprises.

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“…And when was the complex network of signal cascades assembled to sensitize stomatal dynamics to environmental, hormonal, and pathogenic stimuli? The Update review by Franks et al (2017) revisits these questions across temporal and spatial scales. Brodribb and McAdam (2017) highlight a selection of evolutionary boundaries and transitions in relation to signaling by the hormone abscisic acid.…”

mentioning

confidence: 99%

“…The Update reviews by Buckley (2017) and Franks et al (2017) address this background, highlighting major gaps that remain to be bridged, notably between the microscopic and macroscopic scales of the guard cell and the plant canopy as well as between deterministic and global phenomenological approaches. Deans et al (2017) refine a hydraulic model and propose a link to hormonal signaling in conifers.…”

mentioning

confidence: 99%