Atmospheric CO2 Enrichment Increases Plant Water Acquisition
Lack of water poses a significant limitation to vegetative growth and development, especially in arid regions, but rising atmospheric CO2 concentrations are making it ever easier for plants to cope with this stress.

In a review of 55 experiments, one team of researchers found that the growth enhancement caused by a 300-ppm increase in atmospheric CO2 jumped from 31% when water supplies were optimal to 63% when they were less than optimal; while for a CO2 increase of 600 ppm, the CO2-induced growth enhancement jumped from 51% to 219% when water availability went from adequate to less-than-adequate.  This beneficial response occurs because, during times of water stress, atmospheric CO2 enrichment often stimulates plants to develop larger-than-usual and more robust root systems to probe greater volumes of soil for scarce and much-needed moisture.

Atmospheric CO2 enrichment thus increases plant water acquisition, by stimulating root growth, while it also reduces plant water loss by constricting stomatal apertures; and these dual effects typically enhance plant water-use efficiency, even under conditions of less-than-optimal soil water content.  And just as in the case of other extreme environmental stresses such as light deprivation or high temperatures, atmospheric CO2 enrichment can sometimes mean the difference between even a mature plant's living or dying at very low levels of soil moisture.