Physiological framework for adaptation of stomata to CO 2 from glacial to future concentrations

Abstract

In response to short-term fluctuations in atmospheric CO 2 concentration, c a , plants adjust leaf diffusive conductance to CO 2 , g c , via feedback regulation of stomatal aperture as part of a mechanism for optimizing CO 2 uptake with respect to water loss. The operational range of this elaborate control mechanism is determined by the maximum diffusive conductance to CO 2 , g c(max) , which is set by the size ( S ) and density (number per unit area, D ) of stomata on the leaf surface. Here, we show that, in response to long-term exposure to elevated or subambient c a , plants alter g c(max) in the direction of the short-term feedback response of g c to c a via adjustment of S and D . This adaptive feedback response to c a , consistent with long-term optimization of leaf gas exchange, was observed in four species spanning a diverse taxonomic range (the lycophyte Selaginella uncinata , the fern Osmunda regalis and the angiosperms Commelina communis and Vicia faba ). Furthermore, using direct observation as well as flow cytometry, we observed correlated increases in S , guard cell nucleus size and average apparent 1C DNA amount in epidermal cell nuclei with increasing c a , suggesting that stomatal and leaf adaptation to c a is linked to genome scaling.