Does precipitation mediate the effects of elevated CO2 on plant growth in the grass species Stipa grandis?

• Precipitation could adjust the effects of CO2 enrichment on Stipa grandis, the effects of elevated CO2 would be weakened under serious water deficit.
• Increased precipitation promoted total leaf area mainly attributing to the increase of leaf numbers; however, elevated CO2 increased total leaf area by enlarging single leaf area.
• Elevated CO2 limited nocturnal respiration (Rn) by decreasing leaf nitrogen, but precipitation influenced Rn mainly by changing both leaf mass per area (LMA) and nocturnal stomatal conductance (gsn).

Elevated atmospheric CO2 concentrations and the simultaneous change in precipitation patterns jointly affect plant growth directly or indirectly. The temperate grassland in northern China is primarily located in arid and semi-arid regions and is sensitive to climatic change, particularly to changes in precipitation. Understanding the effects of precipitation on temperate grasslands is essential to the development of countermeasures to cope with the negative effects of climate change. In this study, we aimed to quantify the effects of precipitation and elevated CO2 by exploring the eco-physiological mechanisms of Stipa grandis (a dominant species in typical steppe), which included tests of morphological parameters, photosynthetic capacity, dark respiration (Rn) and biomass accumulation, using open-top chambers (OTCs). S. grandis showed a photosynthetic down-regulation under elevated CO2 due to the decrease in leaf nitrogen (N). Rn was limited by elevated CO2 as a result of the dilution of leaf N, but the effect of precipitation change on Rn was primarily attributed to the change in leaf mass per area (LMA) and nocturnal stomatal conductance (gsn). Precipitation increased the total leaf area primarily by increasing leaf numbers; however, elevated CO2 increased the total leaf area by enlarging the single leaf area. Under conditions of either a serious deficit or an abundance of precipitation, the effect of elevated CO2 on plant biomass was weakened. Thus, Precipitation change mediated the effects of elevated CO2 on S. grandis.