Does Size Matter? Atmospheric CO2 May Be a Stronger Driver of Stomatal Closing Rate Than Stomatal Size in Taxa That Diversified under Low CO2.

Caroline Elliott-Kingston,Matthew Haworth,Sven P Batke,Tracy Lawson,Jennifer C Mcelwain,Jon M Yearsley

doi:10.3389/fpls.2016.01253

Caroline Elliott-Kingston, Matthew Haworth + Show 4 more

Open Access

https://doi.org/10.3389/fpls.2016.01253

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Abstract

One strategy for plants to optimize stomatal function is to open and close their stomata quickly in response to environmental signals. It is generally assumed that small stomata can alter aperture faster than large stomata. We tested the hypothesis that species with small stomata close faster than species with larger stomata in response to darkness by comparing rate of stomatal closure across an evolutionary range of species including ferns, cycads, conifers, and angiosperms under controlled ambient conditions (380 ppm CO2; 20.9% O2). The two species with fastest half-closure time and the two species with slowest half-closure time had large stomata while the remaining three species had small stomata, implying that closing rate was not correlated with stomatal size in these species. Neither was response time correlated with stomatal density, phylogeny, functional group, or life strategy. Our results suggest that past atmospheric CO2 concentration during time of taxa diversification may influence stomatal response time. We show that species which last diversified under low or declining atmospheric CO2 concentration close stomata faster than species that last diversified in a high CO2 world. Low atmospheric [CO2] during taxa diversification may have placed a selection pressure on plants to accelerate stomatal closing to maintain adequate internal CO2 and optimize water use efficiency.

Highlights

Stomata are microscopic pores on aerial surfaces of land plants, surrounded by guard cells that adjust turgor in order to regulate pore size, controlling gas exchange between the plant interior and atmosphere
The second fastest responder was the cycad L. peroffskyana, which had the largest stomata of all species studied (SPL: 35.6 ± 5.5 μm; Table 1)
Using current knowledge on the date of diversification of the seven species studied, and estimated atmospheric composition at that time, we showed that the five species that diversified under low or declining atmospheric CO2 concentration (280– 805 ppm) had faster stomatal closing response times than the two species that diversified under high atmospheric CO2 concentration (912–2280 ppm; median halfclosure time 25.27–78.69 min; mean half-closure time 30.13– 105.49 min; Figures 2 and 3; Table 1)

Summary

Introduction

Stomata are microscopic pores on aerial surfaces of land plants, surrounded by guard cells that adjust turgor in order to regulate pore size, controlling gas exchange between the plant interior and atmosphere. Cooling and is determined by density and size of stomata along with functional responses such as rate of aperture change. Stomatal density (SD) and size determine maximum gas diffusion rate (Brown and Escombe, 1900; Parlange and Waggoner, 1970; Raschke, 1976; Wong et al, 1979; McElwain and Chaloner, 1995; Hetherington and Woodward, 2003; Franks and Beerling, 2009; McElwain et al, 2016). Density and size are linked and both are often correlated with atmospheric carbon dioxide concentration ([CO2]atm; Hetherington and Woodward, 2003; McElwain et al, 2005; Franks and Beerling, 2009)

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