The influence of stomatal morphology and distribution on photosynthetic gas exchange

Summary

The intricate and interconnecting reactions of C ₃ photosynthesis are often limited by one of two fundamental processes: the conversion of solar energy into chemical energy, or the diffusion of CO ₂ from the atmosphere through the stomata, and ultimately into the chloroplast. In this review, we explore how the contributions of stomatal morphology and distribution can affect photosynthesis, through changes in gaseous exchange. The factors driving this relationship are considered, and recent results from studies investigating the effects of stomatal shape, size, density and patterning on photosynthesis are discussed. We suggest that the interplay between stomatal gaseous exchange and photosynthesis is complex, and that a disconnect often exists between the rates of CO ₂ diffusion and photosynthetic carbon fixation. The mechanisms that allow for substantial reductions in maximum stomatal conductance without affecting photosynthesis are highly dependent on environmental factors, such as light intensity, and could be exploited to improve crop performance.

Significance Statement

Plant photosynthesis relies on diffusion of CO ₂ from the atmosphere to the chloroplasts through the stomatal pores. The distribution and morphological characteristics of stomata influence this and are of particular importance when attempting to understand or improve on rates of carbon fixation. Nonetheless, alterations expected to affect stomatal conductance do not always cause corresponding alterations in photosynthetic carbon assimilation. This review explores the factors that are likely to cause this observed disconnect between maximum stomatal conductance and photosynthesis.