Responses of a C3and a C4perennial grass to elevated CO2and temperature under different water regimes

摘要

AbstractAn experiment was carried out to determine the effects of elevated CO2, elevated temperatures, and altered water regimes in native shortgrass steppe. Intact soil cores dominated byBouteloua gracilis, a C4perennial grass, orPascopyrum smithii, a C3perennial grass, were placed in growth chambers with 350 or 700 μL L−1atmospheric CO2, and under either normal or elevated temperatures. The normal regime mimicked field patterns of diurnal and seasonal temperatures, and the high‐temperature regime was 4 °C warmer. Water was supplied at three different levels in a seasonal pattern similar to that observed in the field.Total biomass after two growing seasons was 19 greater under elevated CO2, with no significant difference between the C3and C4grass. The effect of elevated CO2on biomass was greatest at the intermediate water level. The positive effect of elevated CO2on shoot biomass was greater at normal temperatures inB. gracilis, and greater at elevated temperatures inP. smithii.Neither root‐to‐shoot ratio nor production of seed heads was affected by elevated CO2.Plant tissue N and soil inorganic N concentrations were lower under elevated Co2, but no more so in the C3than the C4plant. Elevated CO2appeared to increase plant N limitation, but there was no strong evidence for an increase in N limitation or a decrease in the size of the CO2effect from the first to the second growing season. Autumn samples of large roots plus crowns, the perennial organs, had 11 greater total N under elevated CO2, in spite of greater N l