Effects of atmospheric CO2 concentration on transpiration and leaf elongation responses to drought in wheat, perennial ryegrass and tall fescue
We studied the effects of atmospheric CO2 concentration ([CO2]) on the leaf growth response to drought in perennial ryegrass, tall fescue and wheat. Plants were grown in growth chambers at either 200 or 800 ppm of CO2. At leaf 6-7 unfolding, half of the plants were subjected to severe drought. Leaf elongation rate (LER) was measured daily, while plant transpiration was continuously recorded gravimetrically. Water-soluble carbohydrate concentration, water and osmotic potentials in the leaf growing zone were measured at drought onset, at mid-drought and at the time of leaf growth cessation. [CO2] caused stomata closure and therefore reduction of instantaneous transpiration rate and water loss. As a result, CO2 mitigated the impacts of drought on LER and delayed growth cessation for all three species. For ryegrass, LER and soil relative water content (SRWC) relation was improved with CO2, presumably due to a better stomatal regulation. CO2 did not affect nighttime water potential nor osmotic potential of the growing zone. Related to leaf growth, we observed the main effect of CO2 on tillering but no effect on the plant development. In total, water consumption was similar (wheat, tall fescue) or greater (ryegrass) with CO2.