Effects of atmospheric CO2concentration on transpiration and leaf elongation responses to drought in wheat, perennial ryegrass and tall fescue

ABSTRACT We studied the effects of atmospheric CO 2 concentration ([CO 2 ]) 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 CO 2 . 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. [CO 2 ] caused stomata closure and therefore reduction of instantaneous transpiration rate and water loss. As a result, CO 2 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 CO 2 , presumably due to a better stomatal regulation. CO 2 did not affect nighttime water potential nor osmotic potential of the growing zone. Related to leaf growth, we observed the main effect of CO 2 on tillering but no effect on the plant development. In total, water consumption was similar (wheat, tall fescue) or greater (ryegrass) with CO 2 .