Measurement and control of stomatal resistance

The measurement and control of stomatal resistance in the field

Monteith J. L., Szeicz G., Waggoner P. E., (1965)

Rothamsted Experimental Station, Harpenden, Herts.

Journal of Applied Ecology 2(2): 345-355 – https://doi.org/10.2307/2401484 –

https://www.jstor.org/stable/2401484?origin=crossref

Implications of stomatal response to saturation deficit for the heat balance of vegetation

 

 

by Choudhury B. J., Monteith J. L. (1986)

Hydrological Sciences Branch, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 U.S.A.

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in Agric Forest Meteorol 36: 215–225 – https://doi.org/10.1016/0168-1923(86)90036-5 –

https://www.sciencedirect.com/science/article/pii/0168192386900365

Abstract

The Penman—Monteith equation for transpiration from a uniform stand of vegetation is extended to take account of the response of stomata to the saturation deficit (SD) of air in the canopy.

The main assumption is that stomatal conductance throughout the canopy decreases linearly with a value of the SD calculated from the SD at a reference height adjusted to allow for vertical gradients of temperature and vapour pressure.

In most circumstances, stomata can achieve an equilibrium conductance satisfying both the physics and the physiology of the system. In others, equilibrium is unachievable: stomata cannot remain open because air within the canopy becomes drier as they close — a microclimatic form of feedback.

Calculations for an arable crop and for deciduous and coniferous forest show the extent to which transpiration rate is overestimated (a) when the response of stomata to SD is ignored; and (b) when the vertical gradient of SD is ignored.

Large errors are associated with (a), and (b) is important when stomatal conductance is small because of drought.

 

Chemical closure of stomata and the decrease of transpiration

 

 

Decreasing Transpiration of Field Plants by Chemical Closure of Stomata

by Waggoner P. E., Monteith J. L., Szeicz G. (1964)

 

inNature 201: 97–98 – doi:10.1038/201097b0 –

https://www.nature.com/articles/201097b0

Abstract

Chemicals which close stomata have been described by Zelitch¹. When sprayed on leaf surfaces, the compounds decrease transpiration and photosynthesis of detached leaves² and of maize plants in soil³ by increasing the diffusion resistance of stomata.

When sprayed on intact tobacco plants in the greenhouse² or on sunflowers growing in bins of soil outdoors³, the compounds reduced the loss of water from the soil. It remained to demonstrate the effect of chemical closure of stomata on transpiration by a population of plants in the field.

Measurement and Control of Stomatal Resistance in the Field

 

 

The Measurement and Control of Stomatal Resistance in the Field

by Monteith J. L., Szeicz G., Waggoner P. E. (1965)

Rothamsted Experim. Station, Harpenden, Herts., UK

in Journal of Applied Ecology 2(2) : 345-355 – DOI: 10.2307/2401484 –

https://www.jstor.org/stable/2401484?seq=1#page_scan_tab_contents

Abstract

The rate of evaporation from a crop is expressed in terms of weather parameters and a quantity rs derived from profiles of temperature, humidity, and wind. In transfer equations, rs is formally similar to the diffusion resistance of the stomata in a single leaf, and measurements in a field of barley support the hypothesis that rs is the diffusion resistance of the complete crop canopy.

The resistance is relatively small when the leaf area index is great, when soil is moist, and when sunlight is bright. It increases as the plants mature, but is independent of wind speed and is therefore unrelated to the rate of diffusion by turbulent mixing.

More directly, rs was correlated with stomatal resistance rp measured on individual leaves with a porometer. From seventy-five sets of porometer readings taken when the leaf area index was between 6 and 10, the relation was rp = 1.11+0.87 rs Because rp was measured on upper, sunlit leaves, which were more porous than lower, shaded leaves, the ratio of rp to rs was expected, and was found, to be less than the leaf area index.

Finally, stomata were closed and rp was increased by spraying the top of the canopy with NSA (the methyl ester of nonenyl succinic acid). The increase of rs calculated from the decrease of transpiration rate was consistent with the change of rp.

Stomatal turgor mechanism

Photo credit: JXB

Fig. 5.

Images of stoma 1 from the experiment shown in Fig. 4 during a peak of the oscillation (a) and in the closed state 6 min later (b). The time of observation is also marked by arrows in Fig. 4. The arrow in (a) points to the slightly open pore.

Stomatal oscillations at small apertures: indications for a fundamental insufficiency of stomatal feedback‐control inherent in the stomatal turgor mechanism

by Kaiser H., Kappen L. (2001)

in J. Exp. Bot. (2001) 52 (359):1303-1313. – doi:10.1093/jexbot/52.359.1303. 

Abstract

Continuous measurements of stomatal aperture simultaneously with gas exchange during periods of stomatal oscillations are reported for the first time. Measurements were performed in the field on attached leaves of undisturbed Sambucus nigra L. plants which were subjected to step‐wise increases of PPFD. Oscillations only occurred when stomatal apertures were small under high water vapour mole fraction difference between leaf and atmosphere (Δ_W). They consisted of periodically repeated opening movements transiently leading to very small apertures. Measurements of the area of the stomatal complex in parallel to the determination of aperture were used to record volume changes of guard cells even if stomata were closed. Stomatal opening upon a light stimulus required an antecedent guard cell swelling before a slit occurred. After opening of the slit the guard cells again began to shrink which, with some delay, led to complete closure. Opening and closing were rhythmically repeated. The time‐lag until initial opening was different for each individual stoma. This led to counteracting movements of closely adjacent stomata. The tendency to oscillate at small apertures is interpreted as being a failure of smoothly damped feedback regulation at the point of stomatal opening: Volume changes are ineffective for transpiration if stomata are still closed; however, at the point of initial opening transpiration rate rises steeply. This discontinuity together with the rather long time constants inherent in the stomatal turgor mechanism makes oscillatory overshooting responses likely if at high Δ_W the ‘nominal value’ of gas exchange demands a small aperture.

Read the full article: JXB