title: Elevated CO2 can modify the response to a water status gradient in a steppe grass: from cell organelles to photosynthetic capacity to plant growth.
abstract: The atmospheric CO2 concentration is rising continuously, and abnormal precipitation may occur more frequently in the future. Although the effects of elevated CO2 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 CO2 and a water status gradient on the growth, photosynthetic capacity, and mesophyll cell ultrastructure of a dominant grass from a degraded grassland.
  
  
  
  Elevated CO2 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 CO2 under moderate drought, but inhibited with over-watering. Severe drought distorted mesophyll cell organelles, but CO2 enrichment partly alleviated this effect. Intrinsic water use efficiency (WUEi) and total biomass water use efficiency (WUEt) were increased by elevated CO2, regardless of water status. Plant structural traits were also found to be tightly associated with photosynthetic potentials.
  
  
  
  The results indicated that CO2 enrichment alleviated severe and moderate drought stress, and highlighted that CO2 fertilization's dependency on water status should be considered when projecting key species' responses to climate change in dry ecosystems.
authors.affiliation: State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Xiangshan, Haidian, Beijing, 100093, China.
authors.forename: Yanling
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Xiangshan, Haidian, Beijing, 100093, China. xuzz@ibcas.ac.cn.
authors.forename: Zhenzhu
authors.initials: Z
authors.lastname: Xu
authors.affiliation: State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Xiangshan, Haidian, Beijing, 100093, China. gszhou@ibcas.ac.cn.|Chinese Academy of Meteorological Sciences, China Meteorological Administration, 46 Zhongguancun South Street, Haidian, Beijing, 100081, China. gszhou@ibcas.ac.cn.
authors.forename: Guangsheng
authors.initials: G
authors.lastname: Zhou
authors.affiliation: State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, 20 Nanxincun, Xiangshan, Haidian, Beijing, 100093, China.|Chinese Academy of Meteorological Sciences, China Meteorological Administration, 46 Zhongguancun South Street, Haidian, Beijing, 100081, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Liu
mesh_terms: D002245:Carbon Dioxide / Q000032:analysis / Q000378:metabolism*; D057231:Climate Change; D055864:Droughts; D017753:Ecosystem; D015388:Organelles / Q000378:metabolism*; D010788:Photosynthesis; D006109:Poaceae / Q000254:growth & development / Q000378:metabolism*; D014867:Water / Q000032:analysis / Q000378:metabolism*
chemical_list: D014867:Water; D002245:Carbon Dioxide
keywords: Elevated CO2; Grassland; Mesophyll cell organelle; Photosynthetic capacity; Plant growth analysis; Water status gradient