Background
The authors write that "predicting future ecosystem functioning requires a mechanistic understanding of how plants cope with different stressors under future climate conditions with elevated CO2 concentrations and warmer temperatures." However, they say that "studies of stress responses under combined elevated CO2 and warming remain scarce."

What was done
In a study designed to reduce this experimental scarcity, Naudts et al. "assembled grassland communities in sunlit, climate-controlled greenhouses and subjected these to three stressors (drought, zinc toxicity, nitrogen limitation) and their combinations," where "half of the communities were exposed to ambient climate conditions (current climate) and the other half were continuously kept at 3°C above ambient temperatures and at 620 ppm CO2 (future climate)."

What was learned
In the words of the nine researchers, "across all stressors and their combinations, future climate-grown plants coped better with stress, i.e. above-ground biomass production was reduced less in future than in current climate." They also state that "among several tested potential biochemical and ecophysiological stress-relief mechanisms, we found three mutually non-exclusive mechanisms underpinning an improved stress protection under future climate conditions: (i) altered sugar metabolism; (ii) up-regulated levels of total antioxidant capacity and polyphenols; and (iii) more efficient use of ascorbate and glutathione as antioxidants."

What it means
As for what this all means, Naudts et al. say "there could be worldwide implications connected to the alleviation of the stress impact on grassland productivity under future climate conditions," noting as an example that "enhanced protection against drought could mitigate anticipated productivity losses in regions where more frequent and more intense droughts are predicted."