Reconciling the optimal and empirical approaches to modelling stomatal conductance

Medlyn, Belinda E.; Duursma, Remko A.; Eamus, Derek; Ellsworth, David S.; Prentice, I. C.; Barton, Craig V. M.; Crous, Kristine Y.; Angelis, Paolo De; Freeman, Michael L.; Wingate, Lisa

doi:10.1111/j.1365-2486.2012.02790.x

Cited by 196 publications

(378 citation statements)

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“…Although several innovative studies have applied optimization theory to model plant gas exchange (Lloyd and Farquhar, 1994;Buckley, 2008;Katul et al, 2010;Medlyn et al, 2011;Bonan et al, 2014), it has not been as widely adopted as might have been expected from such an elegant theory. Stomatal control of leaf gas exchange was formulated in terms of optimization theory almost four decades ago (Cowan and Farquhar, 1977), but stomatal control has been modeled predominantly using semiempirical or hybrid mechanisticempirical approaches (Damour et al, 2010).…”

Section: Modeling Stomatal Conductance At All Scales Is Underpinned Bmentioning

confidence: 99%

“…et al, Medlyn et al, 2011). The prefix semi applies because empirical stomatal conductance models are actually founded on solid physiological theory, and all practical applications of mechanistic and optimization models require empirical or other mathematical simplifications, so, in practice, none of the models fits purely into one category.…”

Section: Modeling Stomatal Conductance At All Scales Is Underpinned Bmentioning

confidence: 99%

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

et al. 2017

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Section: Modeling Stomatal Conductance At All Scales Is Underpinned Bmentioning

confidence: 99%

Section: Modeling Stomatal Conductance At All Scales Is Underpinned Bmentioning

confidence: 99%

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

et al. 2017

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“…Stomatal conductance may be independently reduced in the future by higher water use efficiency under elevated CO 2 , with relative reductions on the order of about ∼20% predicted by both modelling and experimental work [17][18][19] . Here, we report relative reductions in G S driven by rising VPD on the order of 10% in most forest ecosystems, which would imply even greater relative reductions in canopy stomatal conductance since G S is influenced by soil conductance, which is not sensitive to VPD.…”

mentioning

confidence: 99%

“…Here, we report relative reductions in G S driven by rising VPD on the order of 10% in most forest ecosystems, which would imply even greater relative reductions in canopy stomatal conductance since G S is influenced by soil conductance, which is not sensitive to VPD. While VPD and CO 2 concentrations are assumed to be independent drivers of stomatal conductance in theoretical formulations 17,19 , the extent to which their effects on stomatal conductance are additive remains an important topic for future work, which must also consider the confounding effects of increasing leaf area index 29 .…”

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confidence: 99%

The increasing importance of atmospheric demand for ecosystem water and carbon fluxes

et al. 2016

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Soil moisture supply and atmospheric demand for water independently limit-and profoundly a ect-vegetation productivity and water use during periods of hydrologic stress [1][2][3][4] . Disentangling the impact of these two drivers on ecosystem carbon and water cycling is di cult because they are often correlated, and experimental tools for manipulating atmospheric demand in the field are lacking. Consequently, the role of atmospheric demand is often not adequately factored into experiments or represented in models 5-7 . Here we show that atmospheric demand limits surface conductance and evapotranspiration to a greater extent than soil moisture in many biomes, including mesic forests that are of particular importance to the terrestrial carbon sink 8,9 . Further, using projections from ten general circulation models, we show that climate change will increase the importance of atmospheric constraints to carbon and water fluxes in all ecosystems. Consequently, atmospheric demand will become increasingly important for vegetation function, accounting for >70% of growing season limitation to surface conductance in mesic temperate forests. Our results suggest that failure to consider the limiting role of atmospheric demand in experimental designs, simulation models and land management strategies will lead to incorrect projections of ecosystem responses to future climate conditions. Ecosystem moisture stress is often characterized by changes in soil water availability 10,11 . Declining soil moisture impedes the movement of water to evaporating sites at the soil or leaf surface 12 , reducing the surface conductance to water vapour (G S )-a key determinant of carbon and water cycling-and thereby evapotranspiration (ET). However, atmospheric demand for water, which is directly related to the atmospheric vapour pressure deficit (VPD), also affects G S and ET. Plants close their stomata to prevent excessive water loss when VPD is high [13][14][15][16] and thus, increases in VPD during periods of hydrologic stress represent an independent constraint on plant carbon uptake and water use in ecosystems.While the plant physiological community has long recognized the critical role of VPD in determining plant functioning, VPD is often overlooked in many fields of hydrologic and climate science. For example, precipitation manipulation experiments are frequently used to draw conclusions about ecosystem response to drought stress, even though VPD is unaffected by precipitation manipulation 10 . Some terrestrial ecosystem and ecohydrological models do not permit stomatal conductance to vary with atmospheric demand 5,11 . Many models designed to capture these impacts rely on empirical parameterizations for soil moisture and VPD stress that promote compensating effects and model equifinality 5 , and/or use relative humidity instead of VPD as the primary driver, with significant consequences for projections of

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“…temperature, VPD, CO 2 ) have been derived from leaf level measurements (e.g. [43][44][45][46][47]) and are commonly applied in Earth System Models to represent gas exchange between plants and the environment. Although our leaf level understanding of stomatal response to changing CO 2 and other environmental conditions is relatively well constrained by data, our understanding of ecosystem scale response is still uncertain.…”

Section: Carbon Dioxidementioning

confidence: 99%

Plants and Drought in a Changing Climate

Swann¹

2018

Preprint

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Purpose of review Climate is changing in response to rising concentrations of atmospheric CO 2 and it is commonly asserted that this will cause droughts to become more frequent and severe. However, different metrics of drought give diverging estimates of future impacts. I present a summary of the significant yet underappreciated influence that plant stomatal and growth responses to CO 2 have on drought, and highlight new insights into the impacts of drought on plants in a warmer world. Recent findings Plants influence the water availability on land, and thus reduce the duration and intensity of droughts under higher CO 2 conditions. Plants are concurrently more vulnerable to mortality when droughts occur under hotter conditions. Summary The frequency and severity of drought in the future depends on the response of plants to a changing climate-ignoring plant responses leads to over-prediction of drought. Nonetheless, the impact of current frequencies of drought on plants could lead to higher mortality rates in the future as plants must withstand drought stress simultaneously with hotter temperatures.

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Reconciling the optimal and empirical approaches to modelling stomatal conductance

Cited by 196 publications

References 0 publications

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

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

The increasing importance of atmospheric demand for ecosystem water and carbon fluxes

Plants and Drought in a Changing Climate

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