Variation in stomatal aperture in leaves of Avena fatua L. observed by low‐temperature scanning electron microscopy

Abstract

Abstract. A novel technique to record the variability of stomatal aperture over the leaf surface is described. This combines observations of leaf surfaces using low‐temperature scanning electron microscopy (LTSEM), with digital image analysis to produce the most accurate aperture measurements obtained to date. Leaf samples are rapidly immobilized by cryo‐fixation in liquid nitrogen and stored in a purpose‐built cryo‐storage system. Specimens can be collected in the field, remote from the cryopreparation system, and stored for up to several weeks before being examined on the LTSEM. The advantages of this method are that the time frame of the measurements is accurately known, and is identical for all stomatal apertures in a sample, and the precision of the measurements is not limited by the resolving power of the microscope. Measurements of stomatal aperture were obtained from leaves of field grown Avena fatua using the above procedure. Leaf surface conductance (gsur) was determined by porometry immediately before cryo‐fixation of the same region of the leaf. Measurements of aperture size showed a high degree of variability within each specimen, with coefficients of variation similar to those found in previous studies. Stomatal conductance (gs) was calculated from stomatal dimensions using formulae derived elsewhere. A linear regression between the computed values of gs and porometric estimates of gsur showed good agreement with the regression line passing through the origin with a slope of 1.0 (R2=0.96). Applications of the experimental system are discussed.

Fossil evidence for low gas exchange capacities for Early Cretaceous angiosperm leaves

“…A key problem is that stomata function through movement. Animate functioning means that experimentally difficult-to-test assumptions must invariably be made about what length-to-width ratios (P L :P W ) of the pore define the maximal diffusive potential (Van Gardingen et al 1989;Kaiser 2009). The standard approach has been to assume that maximal width is a constant fraction of the pore length (Osborne et al 2004;Franks and Beerling 2009).…”

Ecophysiological responses of plants to global environmental change since the Last Glacial Maximum

“…Stomatal aperture lengths were measured from acetate replicas previously prepared for stomatal density counts. Although there may be some loss of accuracy in measurements of less than 2 /mi made from acetate replicas (Van Gardingen, Jeffree & Grace, 1989), this problem of accuracy did not arise in the present study because all the aperture lengths were > 10 //m. A potential source of error in making measurements from herbarium material is leaf shrinkage resulting in an under-estimation of true aperture length.…”

“…96 %) thus providing good validation of the accuracy of the method (Van Gardingen et al, 1989). D' is a modification of the equation of Van Gardingen et al (1989) which enables the effect of temperature changes on the diffusivity of water vapour to be incorporated.…”

“…Van Gardingen et al (1989) found that image analysis estimates of stomatal width tended to overestimate g,; these authors therefore incorporated an end correction, involving total pore area. This measurement was not available in the present study so instead the model was calibrated against the data of Van Gardingen et al (1989) and corrections applied at small ( ^ 3 /<m) aperture widths.…”

“…This measurement was not available in the present study so instead the model was calibrated against the data of Van Gardingen et al (1989) and corrections applied at small ( ^ 3 /<m) aperture widths. The depth of the diffusive pathway was estimated by sectioning the fresh Scottish leaves (mean = 13 + 1 /im).…”