Research paper
Effects of spatial scale on stomatal control of transpiration

https://doi.org/10.1016/0168-1923(91)90010-NGet rights and content

Abstract

In an earlier treatment, we used the concept of coupling between vegetation and the atmosphere to demonstrate how the sensitivity of transpiration to a change in stomatal conductance decreases as the spatial scale increases from leaf to region. We introduced the omega coefficient to define the degree of coupling quantitatively and showed the increasing dependence of transpiration on radiation and decreasing dependence on saturation deficit with the increase in scale.

Whilst this approach was effective for this limited purpose, it was not capable of easy extension to include other variables and it does not clearly demonstrate the reasons for the changes in sensitivity of transpiration to the stomata and the changes in emphasis on environmental driving variables as the scale increases.

In the present treatment, we develop the thesis that increasing scale leads to an increase in number of negative feedback paths that stabilise the system and diminish the sensitivity of transpiration to change in stomatal conductance. We show that a consequence of negative feedback at the leaf and canopy scales is that we need only crude models of stomatal response to environmental variables so long as the ratio of stomatal conductance to the boundary-layer conductances is large, but we need rather better models where this ratio is small.

At the regional scale, the effects of the negative feedbacks acting through the planetary boundary layer are even stronger, so that the boundary-layer conductances are of little effect, and we have no need for complex multi-layer models over a wide range of large canopy conductances. When water stress causes stomatal closure, however, the importance of the stomatal and canopy conductances increases so that we need more reliable estimates of them, but there is still no benefit to be gained from multi-layer models. When the supply of water completely dominates transpiration and canopy conductance is very small, crude models again suffice.

References (52)

  • T.P. Meyers et al.

    Modelling the plant canopy micrometeorology with higher-order closure principles

    Agric. For. Meteorol.

    (1987)
  • J.L. Monteith

    Porometry and base line analysis: the case for compatibility

    Agric. For. Meteorol.

    (1990)
  • K.T. Paw U et al.

    Applications of solutions to non-linear energy budget equations

    Agric. For. Meteorol.

    (1988)
  • J.B. Stewart

    Modelling surface conductance of pine forest

    Agric. For. Meteorol.

    (1988)
  • P.J. Aphalo et al.

    Do stomata respond to relative humidity?

  • J.T. Ball et al.

    A model predicting stomatal conductance and its contribution to the control of photosynthesis under different environmental conditions

  • J.A. Bunce

    Effect of boundary layer conductance on the response of stomata to humidity

    Plant Cell Environ.

    (1985)
  • H.A.R. De Bruin

    Physical aspects of the planetary boundary layer with special reference to regional evapotranspiration

  • J.J. DiStefano et al.

    Feedback and Control Systems

  • G.D. Farquhar et al.

    Gain of the feedback loop involving carbon dioxide and stomata: theory and measurement

    Plant Physiol.

    (1978)
  • J. Goudriaan

    Crop Micrometeorology: A Simulation Study

  • J. Grace et al.

    The boundary layer over a Populus leaf

    J. Exp. Bot.

    (1976)
  • D.A. Grantz et al.

    Stomatal response to humidity in a sugarcane field: simultaneous porometric and micrometeorological measurements

    Plant Cell Environ.

    (1990)
  • S.B. Idso et al.

    Foliage temperature: effects of environmental factors with implications for plant water stress assessment and the CO2/climate connection

    Water Resour. Res.

    (1986)
  • S.B. Idso et al.

    The perils of porometry

  • P.G. Jarvis

    The interpretation of the variations in leaf water potential and stomatal conductance found in canopies in the field

    Philos. Trans. R. Soc. London, Ser. B

    (1976)
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