CO2 and stomatal conductance

Chapter 4.04 – Effects of Carbon Dioxide Enrichment on Plants

Taub D. R., Wang X. (2013)

Southwestern University, Georgetown, TX, USA / Indiana University-Purdue University Indianapolis, Indianapolis, IN, USA

in Reference Module in Earth Systems and Environmental Sciences – Climate Vulnerability – Understanding and Addressing Threats to Essential Resources 4: 35-50 – https://doi.org/10.1016/B978-0-12-384703-4.00404-4 –

https://www.sciencedirect.com/science/article/pii/B9780123847034004044

Abstract

Increasing concentrations of atmospheric CO₂ over the next decades can be expected to have important implications for plants. Many plant species are likely to exhibit higher rates of photosynthesis and growth, decreased water consumption and changes in tissue chemistry, including decreased concentrations of protein and minerals. The most likely threats to ecosystem services as a result of increased atmospheric CO₂ are (1) decreased crop and forage food values due to decreased concentrations of protein and minerals and (2) undesirable changes in plant community composition, including increases in populations of some major weed species.

4.04.2.1.2 Transpiration and Water Use

Atmospheric concentrations of CO₂ can also affect plant water use. Carbon dioxide concentrations play a central role in controlling the aperture of stomata, small pores on the surfaces of plants, particularly on the underside of leaves. Open stomata provide a pathway for CO₂ to diffuse into leaves for photosynthesis, but also a pathway for water to diffuse out from leaves. Stomatal aperture (closely related to a physiological measure known as stomatal conductance) is therefore regulated to balance the goals of maintaining CO₂ assimilation and minimizing water loss. At higher concentrations of atmospheric CO₂, plants are able to achieve high rates of photosynthesis with relatively low stomatal conductance. In FACE experiments, elevated CO₂ decreases stomatal conductance by an average of 22% (Ainsworth and Rogers 2007).

Effects of elevated CO₂ on water use by whole plants or plant communities will depend not only on effects on stomatal conductance and leaf-level transpiration, but also on other potential effects of elevated CO₂, such as changes in plant size and morphology. For example, increased growth of plants may lead to increased numbers of leaves, offsetting decreased transpiration per leaf (Warren et al. 2011). Nonetheless, the overall effect of elevated CO₂ appears to be a decrease in total plant and ecosystem water usage, by approximately 5–20% in FACE experiments (Kimball 2010; Leakey et al. 2009). This can lead to alterations of ecosystem hydrology, including an increase in soil moisture and perhaps runoff (Leakey et al. 2009; Norby and Zak 2011).