13.2.2  Stomatal conductance

Printer-friendly version


Tab le 13.1

Increased CO2 concentration generally reduces stomatal conductance, and this is commonly due to a decrease in stomatal aperture, but in some species stomatal density also declines (Table 13.1). Decreased conductance can reduce transpiration. When water is abundant this is of little consequence for a growth response to elevated CO2 because ci (internal concentration of CO2) is still larger and hence photosynthesis is enhanced. However, when plants experience a water deficit, a reduction in conductance enhances the relative growth response to CO2. Because water use is the immediate price plants pay for carbon acquisition, high CO2 can offset a carbon-fixing penalty due to low water supply. In this way water-stressed C4 species show a growth response to CO2 enrichment. In many glasshouse and growth cabinet experiments in pots, plants can suffer water deficits in between their regular waterings. Anomalously large C4 growth responses to CO2 might be attributable to unrecognised water deficits. CO2 × water interactions are described further in Section 13.4.