Hydraulic theory predicts stomatal responses to climatic water deficits

Pragmatic hydraulic theory predicts stomatal responses to climatic water deficits

by Sperry J. S., Wang Y., Wolfe B. T., Mackay D. S., Anderegg W. R. L., McDowell N. G., Pockman W. T. (2016)

John Sperry, Yujie Wang, Brett Wolfe, D. Scott Mackay, William R L Anderegg, Nate McDowell, William Pockman,

Sperry JS1Wang Y2Wolfe BT3Mackay DS4Anderegg WR2McDowell NG5Pockman WT6.

1 Department of Biology, University of Utah, Salt Lake City, UT, 84112, USA.

2 Department of Biology, University of Utah, Salt Lake City, UT, 84112, USA.

3 Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Panama.

4 Department of Geography, State University of New York, Buffalo, NY, 14260, USA.

5 Earth and Environmental Sciences Division, Los Alamos National Lab, Los Alamos, NM, 87545, USA.

6 Biology Department, University of New Mexico, Albuquerque, NM, 87131, USA.

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In New Phytol. 212: 577–589 – DOI: 10.1111/nph.14059

https://www.ncbi.nlm.nih.gov/pubmed/27329266

Abstract

Ecosystem models have difficulty predicting plant drought responses, partially from uncertainty in the stomatal response to water deficits in soil and atmosphere.

We evaluate a ‘supply-demand’ theory for water-limited stomatal behavior that avoids the typical scaffold of empirical response functions. The premise is that canopy water demand is regulated in proportion to threat to supply posed by xylem cavitation and soil drying.

The theory was implemented in a trait-based soil-plant-atmosphere model. The model predicted canopy transpiration (E), canopy diffusive conductance (G), and canopy xylem pressure (Pcanopy ) from soil water potential (Psoil ) and vapor pressure deficit (D). Modeled responses to D and Psoil were consistent with empirical response functions, but controlling parameters were hydraulic traits rather than coefficients.

Maximum hydraulic and diffusive conductances and vulnerability to loss in hydraulic conductance dictated stomatal sensitivity and hence the iso- to anisohydric spectrum of regulation. The model matched wide fluctuations in G and Pcanopy across nine data sets from seasonally dry tropical forest and piñon-juniper woodland with < 26% mean error.

Promising initial performance suggests the theory could be useful in improving ecosystem models. Better understanding of the variation in hydraulic properties along the root-stem-leaf continuum will simplify parameterization

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A dynamic stomatal response resulting in a more conservative strategy for managing hydrologic resources


Figure 1. Map of (a) aspen and (b) maple sites. Large gray circles indicate 5 m and 10 m radius com- petition plots centered on the sap flux trees used for analysis in this study for aspen and maple, respec- tively. On both maps, crosses denote trees from the species used for analysis in this study instrumented for sap flux, and open circles represent trees sampled for sap flux only. The cyclic sampling design is reflected in the clustered location of (and subsequent gaps between) sap flux trees.

Contribution of competition for light to within-species variability in stomatal conductance

by Loranty M. M., Mackay D. S., Ewers B. E., Traver E., Kruger E. L. (2010)

Michael M. Loranty,1,2 – D. Scott Mackay,1 – Brent E. Ewers,3,4 – Elizabeth Traver,3,5 – Eric L. Kruger,6

1 Department of Geography, State University of New York at Buffalo, Buffalo, New York, USA.

2 Now at Woods Hole Research Center, Falmouth, Massachusetts, USA.

3 Department of Botany, University of Wyoming, Laramie, Wyoming, USA.

4 Program in Ecology, University of Wyoming, Laramie, Wyoming, USA.

5 Now at Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire, USA.

6 Department of Forest Ecology and Management, University of Wisconsin!Madison, Madison, Wisconsin, USA.

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In Water Resour. Res. 46: W05516 – ,doi:10.1029/2009WR008125 –

Contribution_of_competition_for_light_to.pdf

Abstract

Sap flux (JS) measurements were collected across two stands dominated by either trembling aspen or sugar maple in northern Wisconsin. Observed canopy transpiration (EC!obs) values derived from JS were used to parameterize the Terrestrial Regional Ecosystem Exchange Simulator ecosystem model.

Modeled values of stomatal conductance (GS) were used to determine reference stomatal conductance (GSref), a proxy for GS that removes the effects of temporal responses to vapor pressure deficit (D) on spatial patterns of GS. Values of GSref were compared to observations of soil moisture, several physiological variables, and a competition index (CI) derived from a stand inventory, to determine the underlying cause of observed variability.

Considerable variability in GSref between individual trees was found, with values ranging from 20 to 200 mmol m-2 s-1 and 20 to 100 mmol m-2 s-1 at the aspen and maple stands, respectively. Model-derived values of GSref and a sensitivity to D parameter (m) showed good agreement with a known empirical relationship for both stands.

At both sites, GSref did not vary with topographic position, as indicated by surface soil moisture. No relationships were observed between GSref and tree height (HT), and a weak correlation with sapwood area (AS) was only significant for aspen.

Significant nonlinear inverse relationships between GSref and CI were observed at both stands. Simulations with uniform reductions in incident photosynthetically active radiation (Q0) resulted in better agreement between observed and simulated EC.

Our results suggest a link between photosynthesis and plant hydraulics whereby individual trees subject to photosynthetic limitation as a result of competitive shading exhibit a dynamic stomatal response resulting in a more conservative strategy for managing hydrologic resources.

A ‘supply-demand’ theory for water-limited stomatal behavior

 

Pragmatic hydraulic theory predicts stomatal responses to climatic water deficits

Sperry J. S., Wang Y., Wolfe B. T., Mackay D. S., Anderegg W. R. L., McDowell N. G., Pockman W. T. (2016)

University of Utahjohn_sperry

University of Utah, Salt Lake City, yujie_wang9

University of Utah, Salt Lake City, brett_wolfe2

University Buffalo, State University New Yorkd_mackay

University of Utah, Salt Lake City, william_anderegg

Nate G. McDowell,

University of New Mexicowilliam_pockman

 

–  – New Phytologist 2016 – DOI: 10.1111/nph.14059 –

https://www.researchgate.net/publication/304330127_Pragmatic_hydraulic_theory_predicts_stomatal_responses_to_climatic_water_deficits

Abstract
Ecosystem models have difficulty predicting plant drought responses, partially from uncertainty in the stomatal response to water deficits in soil and atmosphere.
We evaluate a ‘supply-demand’ theory for water-limited stomatal behavior that avoids the typical scaffold of empirical response functions. The premise is that canopy water demand is regulated in proportion to threat to supply posed by xylem cavitation and soil drying.
The theory was implemented in a trait-based soil-plant-atmosphere model. The model predicted canopy transpiration (E), canopy diffusive conductance (G), and canopy xylem pressure (Pcanopy ) from soil water potential (Psoil ) and vapor pressure deficit (D).
Modeled responses to D and Psoil were consistent with empirical response functions, but controlling parameters were hydraulic traits rather than coefficients. Maximum hydraulic and diffusive conductances and vulnerability to loss in hydraulic conductance dictated stomatal sensitivity and hence the iso- to anisohydric spectrum of regulation.
The model matched wide fluctuations in G and Pcanopy across nine data sets from seasonally dry tropical forest and piñon-juniper woodland with < 26% mean error.
Promising initial performance suggests the theory could be useful in improving ecosystem models. Better understanding of the variation in hydraulic properties along the root-stem-leaf continuum will simplify parameterization.