Sensitivity of stomatal and canopy conductance to elevated CO2 concentration

Sensitivity of stomatal and canopy conductance to elevated CO2 concentration – interacting variables and perspectives of scale

by Wullschleger S. D., Gunderson C. A., Hanson P. J., Wilson K. B., Norby R. J. (2002)

Stan D. Wullschleger, C. A. Gunderson, P. J. Hanson, K. B. Wilson, R. J. Norby,

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In New Phytologist 153: 485–496 – https://doi.org/10.1046/j.0028-646X.2001.00333.x – 

https://nph.onlinelibrary.wiley.com/doi/10.1046/j.0028-646X.2001.00333.x

Abstract

• The hydrological response of forests to rising CO₂ is a critical biotic feedback in the study of global climate change. Few studies, however, have investigated this highly dynamic response at relevant temporal and spatial scales.
• A combination of leaf and whole‐tree measurements and stand‐level extrapolations were used to assess how stomatal conductance, canopy transpiration and conductance, and evapotranspiration might be affected by future, higher CO₂concentrations.
• Midday measurements of stomatal conductance for leaves sampled in a 12‐yr‐old sweetgum (Liquidambar styraciflua) stand exposed to free‐air CO₂ enrichment were up to 44% lower at elevated than at ambient CO₂ concentrations, whereas canopy conductance, averaged over the growing season, was only 14% lower in stands exposed to CO₂ enrichment. The magnitude of this response was dependent on vapor pressure deficit and soil water potential. Annual estimates of evapotranspiration showed relatively small reductions due to atmospheric CO₂ enrichment.
• These data illustrate that the hydrological response of a closed‐canopy plantation to elevated CO₂ depends on the temporal and spatial scale of observation. They emphasize the importance of interacting variables and confirm that integration of measurements over space and time reduce what, at the leaf level, might otherwise appear to be a large and significant response.

Environmental and stomatal control of photosynthetic enhancement in the canopy

 

 

Environmental and stomatal control of photosynthetic enhancement in the canopy of a sweetgum (Liquidambar styraciflua L.) plantation during 3 years of CO2 enrichment

by Gunderson C. A., Sholtis J. D., Wullschleger S. D., Tissue D. T., Hanson P. J. & Norby R. J. (2002)

C. A. GUNDERSON,1 J. D. SHOLTIS,2 S. D. WULLSCHLEGER,1 D. T. TISSUE,2 P. J. HANSON,1 & R. J. NORBY,1

1 Environmental Sciences Division, Oak Ridge National Laboratory, Bldg. 1059, PO Box 2008, Oak Ridge, TN 37831-6422, USA,

2 Department of Biology, Texas Tech University, Lubbock, TX 79409-3131, USA

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in Plant, Cell and Environment 25: 379– 393 – https://doi.org/10.1046/j.0016-8025.2001.00816.x –

https://onlinelibrary.wiley.com/doi/full/10.1046/j.0016-8025.2001.00816.x

Abstract

Light‐saturated photosynthetic and stomatal responses to elevated CO₂ were measured in upper and mid‐canopy foliage of a sweetgum (Liquidambar styraciflua L) plantation exposed to free‐air CO₂ enrichment (FACE) for 3 years, to characterize environmental interactions with the sustained CO₂ effects in an intact deciduous forest stand.

Responses were evaluated in relation to one another, and to seasonal patterns and natural environmental stresses, including high  temperatures, vapour pressure deficits (VPD), and drought. Photosynthetic CO₂ assimilation (A) averaged 46% higher in the +200 µmol mol⁻¹ CO₂ treatment, in mid‐ and upper canopy foliage. Stomatal conductance (g_s) averaged 14% (mid‐canopy) and 24% (upper canopy) lower under CO₂enrichment.

Variations in the relative responses of A and g_s were linked, such that greater relative stimulation of A was observed on dates when relative reductions in g_s were slight. Dry soils and high VPD reduced g_s and A in both treatments, and tended to diminish treatment differences.

The absolute effects of CO₂ on A and g_s were minimized whenever g_s was low (<0·15 mol m⁻² s⁻¹), but relative effects, as the ratio of elevated to ambient rates, varied greatly under those conditions. Both stomatal and non‐stomatal limitations of A were involved during late season droughts.

Leaf temperature had a limited influence on A and g_s, and there was no detectable relationship between prevailing temperature and CO₂ effects on A or g_s. The responsiveness of Aand g_s to elevated CO₂, both absolute and relative, was maintained through time and within the canopy of this forest stand, subject to seasonal constraints and variability associated with limiting air and soil moisture.

Modeling the Stomatal and Biochemical Control of Plant Gas Exchange

 

 

PHOTOBIO: Modeling the Stomatal and Biochemical Control of Plant Gas Exchange

by Wullschleger S. D., Hanson P. J., Sage R. F. (1992)

S. D. Wullschleger and P. J. Hanson, Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6034;

R. F. Sage, Dep. of Botany, Univ. of Georgia, Athens, GA 30602. Publication no. 3922, Environmental Sciences Division, Oak Ridge National Laboratory

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in J. Nat. Resour. Life Sci. Educ. 21: 141-145 –

https://www.crops.org/files/publications/nse/pdfs/jnr021/021-02-0141.pdf

ABSTRACT

Simulation models are increasingly being used to describe physiological processes in the plant sciences. These models, while useful for research purposes, also offer tremendous potential for demonstrating a wide array of scientific concepts to students.

We have developed an educational software package that illustrates the stomatal and biochemical control of transpiration and photosynthesis. The simulation program uses a biochemical model of C assimilation that, when coupled to an empirical submodel describing stomatal conductance, can be solved iteratively for leaf photosynthesis, stomatal conductance, and transpiration.

Graphic and tabular presentations, combined with on-screen requests for student input, serve to effectively convey the basic fundamentals of plant gas-exchange, and the diurnal patterns of photosynthesis and transpiration in response to fluctuating environmental conditions.

More advanced topics focus on the biochemical limitations imposed on photosynthesis by Rubisco activity, electron transport capacity, and the regeneration of inorganic P. Also included is an exercise that challenges students to use the lessons learned to optimize C assimilation, while minimizing water losses, over a 3-d simulation period.

Application of the program can assist instructors in illustrating important concepts regarding stomatal and biochemical control of plant gas-exchange.