Stomatal absorption of SO2 and transpiration by pine needles

 

Photo credit: Google

Scots Pine – Pinus sylvestris

Experimental and numerical analysis of stomatal absorption of sulphur dioxide and transpiration by pine needles.

by Vesala T., Hameri K., Ahonen T., Kulmala M., Hari P., Pohja T., Krissinel E., Shokhirev N., Lushnikov A. A. (1995)

in Atmospheric Environment 29: 825- 836 – https://doi.org/10.1016/1352-2310(94)00312-9

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http://www.sciencedirect.com/science/article/pii/1352231094003129

Abstract

We present the experimental results of flow chamber measurements on SO₂ dry deposition, and of separate field measurements on transpiration of Scots pine (Pinus sylvestris L) twigs under typical northerly summertime conditions.

These results are interpreted by a numerical model, which solves the steady-state diffusion equation for a single stoma approximated to have cylindrical symmetry.

An analytical method to estimate the maximal effect of interference (merging concentration fields of adjacent stomata) between stomatal pores is introduced.

As a result, a functional pore radius is found to be of order of 2–3 μm, which is significantly smaller than the maximal anatomical size of stomatal aperture. This indicates that stomata are capable to transfer vapours to different degrees.

If the obtained estimates for needle resistances are divided by a factor of 4, the leaf area index of local pine canopy, the bulk stomatal resistance for SO₂ is of the order of 200–300 s m⁻¹.

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