During transpiration, water vapor is released from the leaves through small pores or openings called stomates. (scientificamerican.com)
However, more atmospheric CO2 is predicted to increase crop biomass and subsequent yields, and reduce water use by allowing plant stomates to open over shorter periods, thus assimilating the same amount of atmospheric CO2 while conserving moisture (Cutforth et al. 2007). (montanaclimate.org)
It could be that we have reached a level of background tropospheric ozone that is intolerable to vegetation — or it could be the recently mandated addition of ethanol to gasoline, since trees are dying at a rapidly accelerating rate, annual crop yieldsare markedly reduced, and even ornamentals planted in good soil in pots with regular watering exhibit the characteristic damaged stomates on foliage indicative of exposure to ozone. (realclimate.org)