Elevated CO(2) can modify the response to a water status gradient in a steppe grass: from cell organelles to photosynthetic capacity to plant growth

BACKGROUND: The atmospheric CO(2) concentration is rising continuously, and abnormal precipitation may occur more frequently in the future. Although the effects of elevated CO(2) and drought on plants have been well reported individually, little is known about their interaction, particularly over a water status gradient. Here, we aimed to characterize the effects of elevated CO(2) and a water status gradient on the growth, photosynthetic capacity, and mesophyll cell ultrastructure of a dominant grass from a degraded grassland. RESULTS: Elevated CO(2) stimulated plant biomass to a greater extent under moderate changes in water status than under either extreme drought or over-watering conditions. Photosynthetic capacity and stomatal conductance were also enhanced by elevated CO(2) under moderate drought, but inhibited with over-watering. Severe drought distorted mesophyll cell organelles, but CO(2) enrichment partly alleviated this effect. Intrinsic water use efficiency (WUE(i)) and total biomass water use efficiency (WUE(t)) were increased by elevated CO(2), regardless of water status. Plant structural traits were also found to be tightly associated with photosynthetic potentials. CONCLUSION: The results indicated that CO(2) enrichment alleviated severe and moderate drought stress, and highlighted that CO(2) fertilization’s dependency on water status should be considered when projecting key species’ responses to climate change in dry ecosystems. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12870-016-0846-9) contains supplementary material, which is available to authorized users.