Direct inhibition of leaf dark respiration by elevated CO2 is minor in 12 grassland species

Direct inhibition of dark respiration by elevated atmospheric concentration s of CO2 could alter the carbon balance of plants and ecosystems. The short -term response of leaf dark respiration to elevated CO2 concentrations are reported here in 12 grass and forb species of a North American grassland co mmunity. Specific respiration rates at 25 degreesC and a range of measurement CO2 co ncentrations were determined for detached leaves of each species field-grow n in monoculture. On average, respiration rates were 1.8% lower at 700 than at 360 mu mol mol (-1) CO2. Among species, responses ranged from a 6.4% inhibition to a 2.4% stimulation and were generally not statistically significant. Across a rang e of CO2 concentrations from 360 to 1300 mu mol mol(-1), respiration rates declined linearly and were 11% lower at 1300 than 360 mu mol mol(-1) CO2. Direct inhibition of leaf respiration is small compared with other longer-t erm, indirect effects of CO2 on carbon exchange. The direct effects of risi ng atmospheric CO2 concentrations on respiration rates should result in min imal effects on plant carbon exchange in grasslands.