Mid-season gas exchange of an alpine grassland under elevated CO2.
Ecosystem net CO2uptake, evapotranspiration (ET) and night-time CO2efflux were measured in an alpine grassland dominated by Carex curvula, treated with doubled ambient partial pressure of CO2via open-top chambers. One quarter of the plots were treated with mineral nutrients to simulate the effect of lowland nitrogen deposition rates. Depending upon fertilizer supply, ecosystem net CO2uptake per ground area in full sunlight (NCEmax) was 41-81% higher in open-top chambers supplied with doubled ambient partial pressure (pa) of CO2than in plots receiving ambient CO2. Short-term reversals of the CO2level suggest that the extent of downward adjustment of canopy photosynthesis under elevated CO2was 30-40%. ET tended to decline, while water use efficiency (WUE), expressed as the NCEmax:ET ratio, increased more than twofold under elevated CO2. Night-time ecosystem CO2efflux did not respond to changes in CO2pa. NCEmaxand night-time CO2efflux were more responsive to mineral fertilizer than the doubling of CO2. This suggests that in these alpine plant communities, atmospheric nutrient input may induce equal or greater effects on gas exchange than increased CO2.
Botanisches Institut der Universität Basel, Schönbeinstrasse 6, CH-4056, Basel, Switzerland.
Matthias W
MW
Diemer
Altitude; Carbon dioxide; Climate change; Photosynthesis; Water loss