Abstract
BackgroundThe 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.ResultsElevated 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.ConclusionThe 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0846-9) contains supplementary material, which is available to authorized users.
Highlights
The atmospheric CO2 concentration is rising continuously, and abnormal precipitation may occur more frequently in the future
The soil was retrieved from the local soil surface (0–30 cm), and A. cristatum seeds were collected the year before the experiment from the local steppe—a typical grassland ecosystem in Xilinhot (43°38′N, 116°42′E, 1100 m a.s.l.), Inner Mongolia, China
We found that the increase of WUEt with increases in both water use and plant biomass (Fig. 6), at a high CO2 level, might explain the resource limitation to water use efficiency (WUE); both a water use increase and CO2 enrichment, as increases in available resources, might promote WUE by stimulating photosynthetic capacity and plant growth
Summary
The atmospheric CO2 concentration is rising continuously, and abnormal precipitation may occur more frequently in the future. The effects of elevated CO2 include enhanced net photosynthesis rate (Anet), down-regulated stomatal conductance (gs) [3, 7,8,9], dilution of chemical elements [10], imbalance of sink–source relationships [11, 12], increased plant growth and vegetation productivity [2, 13], changes in species competition interactions and community structure [13,14,15], and lengthened growing seasons [16] These elevated CO2-induced changes might be mediated by other environmental factors,
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