Development of water stress under increased atmospheric CO2 concentration

The increase in water use efficiency (the ratio of photosynthetic to transp iration rates) is likely to be the commonest positive effect of long-term e levation in CO2 concentration (CE), This may not necessarily lead to decrea se in long-term water use owing to increased leaf area. However, some plant species seem to cope better with drought stress under CE, because increase d production of photosynthates might enhance osmotic adjustment and decreas ed stomatal conductance and transpiration rate under CE enable plants to ma intain a higher leaf water potential during drought. In addition, at the sa me stomatal conductance, internal CO2 concentration might be higher under C E which results in higher photosynthetic rate. Therefore plants under CE of the future atmosphere will probably survive eventual higher drought stress and some species may even be able to extend their biotope into less favour able sites.