Stomatal dimensions and resistance to diffusion.
TL;DR: The resistance is calculated for general shapes that include the realistic slit and the part of the diffusive resistance per square centimeter determined by stomatal geometry is [Formula: see text] where a, b, d, and n are the semilength, semiwidth, depth, and density of the stomata, and D is the diffusivity.
Abstract: In the past, relations of diffusive resistance to stomatal geometry have concerned circular pores or pores that are replaced by equivalent circles of the same area We calculated the resistance for general shapes that include the realistic slit The resistance comprises two terms The first is an outer resistance that depends only on ventilation and leaf geometry and is independent of stomata The second is an inner resistance and is a function of stomatal interference and of stomatal geometry only If interstomatal spacing is at least three times stomatal length, interstomatal interference is negligible The inner resistance can then be calculated by adding the resistance of the two ends and the throat of each stoma In the case of an elongated stoma, the part of the diffusive resistance per square centimeter determined by stomatal geometry is [Formula: see text] where a, b, d, and n are the semilength, semiwidth, depth, and density of the stomata, and D is the diffusivity This is the familiar Brown and Escombe result applied to slits
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TL;DR: A wide variety of formulae have been developed for estimating evaporation from vegetation that are based entirely on weather variables and take no account at all of the species composition or stomatal properties of the transpiring vegetation.
Abstract: Publisher Summary The study of leaf anatomy and of the mechanisms of the opening and closing of stomatal guard cells leads one to suppose that the stomata constitute the main or even the sole regulating system in leaf transpiration. Meteorologists have developed a wide variety of formulae for estimating evaporation from vegetation that are based entirely on weather variables and take no account at all of the species composition or stomatal properties of the transpiring vegetation. These “potential evaporation” formulae are widely and, to a large degree, successfully used for estimating evaporation from vegetation that is not water-stressed. Transpiration depends on stomatal conductance, net radiation receipt and upon air saturation deficit, temperature, and wind speed. Saturation deficit and wind speed vary through leaf boundary layers, through canopies, and through the atmosphere above the canopies. The sensitivity of saturation deficit to changes in stomatal conductance depends on where the saturation deficit is measured. If all of the stomata on a single leaf change aperture in unison, there may be a substantial change in saturation deficit measured at the leaf surface but a negligible change in saturation deficit measured a centimetre or two away, outside the leaf boundary layer.
1,848 citations
Cites background from "Stomatal dimensions and resistance ..."
...Theoretical studies on diffusion through single pores (Brown and Escombe, 1900; Milthorpe and Penman, 1967; Parlange and Waggoner, 1970 ) and a multitude of studies on single leaves in the leaf cham-...
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01 Apr 1994
TL;DR: In a world of increasing atmospheric CO2, there is intensified interest in the ecophysiology of photosynthesis and more attention is being given to other aspects of carbon exchange and storage in natural ecosystems.
Abstract: In a world of increasing atmospheric CO2, there is intensified interest in the ecophysiology of photosynthesis and more attention is being given to other aspects of carbon exchange and storage in natural ecosystems. For example, how much will the photosynthesis of terrestrial and aquatic vegetation change as global CO2 increases? Are there major ecosystems, such as the boreal forests, which may become important sinks of CO2 and slow down the effects of anthropogenic CO2 emissions on climate? This volume reviews the progress which has been made in understanding photosynthesis in the past few decades at several levels of integration, from the molecular level to canopy, ecosystem and global scales.
886 citations
TL;DR: It is shown that g(min) is of little value as a predictor for drought resistance of crops, with the possible exception of Sorghum bicolor L. Moench.
Abstract: Cuticles act as solution-diffusion membranes for water transport. Diffusion in pores does not contribute to cuticular transpiration. An extensive literature survey of cuticular permeances (P) and minimum leaf conductances (g(min)) to water is presented. The two variables cannot be distinguished with most experimental techniques. Results from different experiments are in good agreement with each other for some species, for example, Fagus sylvatica L., but not for others, such as Picea abies (L.) Karst. In a data set of 313 values of P or g(min) from 200 species, distributions of results obtained with different techniques were found to differ significantly. Likely reasons include water loss from incompletely closed or incompletely sealed stomata, and the dependence of P on moisture content of the cuticle and on storage time of isolated cuticles. Contrasting evidence for an interaction between cuticular transpiration and stomatal sensitivity to air humidity is presented. The occurrence of unusually high g(min) in trees growing at the alpine treeline and its physiological significance are discussed. It is shown that g(min) is of little value as a predictor for drought resistance of crops, with the possible exception of Sorghum bicolor L. Moench. Possible water uptake from fog or dew across cuticles is considered briefly.
441 citations
TL;DR: It is proposed that the ABA-induced changes inStomatal mechanics and stomatal conductance versus P(g) characteristics constitute an improvement in water-use efficiency that may be invoked under prolonged drought conditions.
Abstract: Gas exchange parameters and stomatal physical properties were measured in Tradescantia virginiana plants grown under well-watered conditions and treated daily with either distilled water (control) or 3.0 mM abscisic acid (ABA). Photosynthetic capacity (CO(2) assimilation rate for any given leaf intercellular CO(2) concentration [c(i)]) and relative stomatal sensitivity to leaf-to-air vapor-pressure difference were unaffected by the ABA treatment. However, at an ambient CO(2) concentration (c(a)) of 350 micromol mol(-1), ABA-treated plants operated with significantly lower c(i). ABA-treated plants had significantly smaller stomata and higher stomatal density in their lower epidermis. Stomatal aperture versus guard cell pressure (P(g)) characteristics measured with a cell pressure probe showed that although the form of the relationship was similar in control and ABA-treated plants, stomata of ABA-treated plants exhibited more complete closure at P(g) = 0 MPa and less than half the aperture of stomata in control plants at any given P(g). Scaling from stomatal aperture versus P(g) to stomatal conductance versus P(g) showed that plants grown under ABA treatment would have had significantly lower maximum stomatal conductance and would have operated with lower stomatal conductance for any given guard cell turgor. This is consistent with the observation of lower c(i)/c(a) in ABA-treated plants with a c(a) of 350 micromol mol(-1). It is proposed that the ABA-induced changes in stomatal mechanics and stomatal conductance versus P(g) characteristics constitute an improvement in water-use efficiency that may be invoked under prolonged drought conditions.
261 citations
TL;DR: In this paper, the stomatal response of woody leaves to CO 2 diffusion has been investigated in the Lower Rhine Embayment (Germany, The Netherlands) sediments of the Late Miocene, Pliocene and early Pleistocene.
242 citations
References
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TL;DR: A replicative form isolated by Kaerner and Hoffmann-Berling from E. coli infected with the RNA phage fr shows the same melting profile, Tm, RNAase resistance, and buoyant density in CS2SO4 as the Replicative form of MS2.
Abstract: 5 Weissmann, C., P. Borst, R. H. Burdon, M. A. Billeter, and S. Ochoa, these PROCEEDINGS, 51, 682 (1964). 6Ibid., 890 (1964). 7Burdon, R. H., P. Borst, and C. Weissmann, Federation Proc., 23, 319 (1964). 8 Ochoa, S., C. Weissmann, P. Borst, R. H. Burdon, and M. A. Billeter, Federation Proc., in press. 9 Fenwick, M. L., R. L. Erikson, and R. M. Franklin, Federation Proc., 23, 319 (1964). '0Kaerner, H. C., and H. Hoffmann-Berling, Z. Naturforsch., in press. \"Weissmann, C., L. Simon, and S. Ochoa, these PROCEEDINGS, 49, 407 (1963). 12 Langridge, R., and P. J. Gomatos, Science, 141, 694 (1963). 13Langridge, R., H. R. Wilson, C. W. Hooper, M. H. F. Wilkins, and L. D. Hamilton, J. Mol. Biol., 2, 19 (1960). 14 Mejbaum, W., Z. Physiol. Chem., 258, 117 (1939). 1Dische, Z., in The Nucleic Acids, ed. E. Chargaff and J. N. Davidson (New York: Academic Press, 1955), vol. 1, p. 294. 16 We are indebted to Dr. R. C. Warner for these determinations. 17 Strauss, J. H., Jr., and R. L. Sinsheimer, J. Mol. Biol., 7, 43 (1963). 18 A replicative form isolated by Kaerner and Hoffmann-Berling (ref. 10) from E. coli infected with the RNA phage fr shows the same melting profile, Tm, RNAase resistance, and buoyant density in CS2SO4 as the replicative form of MS2. Although the replicative form of phage fr, purified by the method A of these authors, also sediments with an s20 of about 8.5, their improved method B yielded a preparation containing a minor component with an s20 of 14.5 S. This is the value expected for a duplex containing twice as much RNA as the viral strand. A similar value, of 12-16 S, was obtained by Fenwick et al. (ref. 9) for material tentatively identified as the replicative form of the RNA phage R17 by sucrose gradient analysis of infected E. coli extracts.
734 citations
TL;DR: In the present communication, which is intended to be one of a series descriptive of the researches, the physical phenomena will be confine ourselves to the physiological questions in so far as they are necessary, and the explanations they suggest of certain natural processes in plants and perhaps also in animals.
Abstract: During the course of an investigation which we have been carrying out in the Jodrell Laboratory during the past two or three years, with the ultimate object of extending our knowledge of the process of the fixation of carbon by green plants, we have been led to examine somewhat minutely the purely physical processes by which the carbon dioxide of the atmosphere is in the first place able to gain access to the active centres of assimilation. In following up this line of work we have been led to some unexpected results, and to the discovery of certain facts connected with gaseous and liquid diffusion which have been hitherto unnoticed, and which appear to be of considerable interest, not only in their physical aspects, but also from the explanations they suggest of certain natural processes in plants (and perhaps also in animals) in which the transference of gaseous or dissolved substances depends more or less on diffusivity . In the present communication, which is intended to be one of a series descriptive of our researches, we shall, as far as possible, confine ourselves to the physical phenomena, touching only on the physiological questions in so far as they are necessary.
237 citations
TL;DR: Compared to a steady laminar flow, the turbulence of a realistic wind decreases the resistance by a constant factor of about 2.5; the same constant factor was observed whether the leaf was flapping or not, when the wind velocity was not too low.
Abstract: If the evaporation is uniform on a flat exposed leaf, forced convection will also be nearly uniform, and the leaf temperature will vary with the square root of the distance from the leading edge. Then the resistance expressed in terms of the proper, i.e., average, temperature has the same value as the resistance of a leaf at uniform temperature. Compared to a steady laminar flow, the turbulence of a realistic wind decreases the resistance by a constant factor of about 2.5. The same constant factor was observed whether the leaf was flapping or not, when the wind velocity was not too low.
96 citations