Stomatal area estimation based on stomatal length and width of four Magnoliaceae species: even “kidney”-shaped stomata are not elliptical

Key message

Stomatal area is proportional to the product of stomatal length and width with a proportionality coefficient exceeding π/4 (indicating a deviation from an elliptical shape) for four Magnoliaceae species.

Abstract

Stomatal size is an important factor affecting the photosynthetic and transpiration rates of vascular plants. To examine stomatal morphometrics, we measured the length (L), width (W), and area (A) of 960 stomata from four Magnoliaceae species within two genera (Magnolia and Michelia). Four mathematical models were used to estimate A: (i) A scales as a function of LW, which is referred to as the Montgomery equation (denoted as ME), (ii) A scales as a function of some power of LW, (iii) A scales as a function of L², and (iv) A scales as some power of L. The data show that ME is the best among the four models based on the trade-off between the goodness of fit and model structural complexity, i.e., A is proportional to LW. The ME was verified at the species level and for the pooled data. The proportionality coefficient of ME was affected by stomatal geometry and exceeded the proportionality coefficient predicted for an elliptical shape of stomata (π/4). This study provides a simple and relatively accurate method for measuring stomatal area (e.g., it decreases by 40.1% the root-mean-square error when calculating A using π/4 × LW). In addition, the proportionality coefficient of ME also provides a useful quantitative taxonomic parameter and a method to gauge the response of plants to environmental changes.