Plant response to decreasing soil moisture under rising atmospheric CO₂ levels

Widespread drought driven by global warming is predicted across the 21^st century, just as CO₂ level is projected to as much as double over the same time period. However, the potential interplay between increasing CO₂ and decreasing soil moisture on plant function is uncertain, as previous works have not successfully separated and quantified these two competing effects. Here we evaluated the interaction between soil moisture and CO₂ using stable carbon isotope measurements of Arabidopsis grown under the simultaneous modulation of an exhaustive range of both variables. Results showed that both increasing soil water content and increasing CO₂ increased isotopic discrimination, and that the soil moisture effect was not influenced by the CO₂ level and vice versa. Our data confirm that changes in the carbon isotope record of terrestrial organic matter preserved within the geologic record are best interpreted as deriving from changes in atmospheric CO₂.