摘要：We used the chamber method to measure growing season ecosystem carbon exchange and ecosystem respiration in Finnish alpine tundra. The average ecosystem respiration in the sites was 0.8–0.9 µmol m −2 s −1 and the daytime net ecosystem exchange (NEE) was around −0.4 to −0.5 µmol m −2 s −1 . There were no detectable differences in cuvette-based net ecosystem exchange or ecosystem respiration between grazed fell areas and long term reindeer exclosure. Further analysis showed that net carbon exchange as well as ecosystem respiration were significantly correlated with the dwarf shrub cover, while the proportion of lichen cover ( Cladina sp.) was not correlated with ecosystem carbon exchange. Clipping experiments showed that about half of the measured ecosystem respiration was heterotrophic. Plots that had been protected from reindeer grazing had almost two times higher above-ground plant biomass than grazed plots. The reason for this was 86% lower lichen biomass on the grazed side of the fell, while the biomass of Ericaceous dwarf shrubs did not differ even though there were changes in species composition. Surprisingly, the proportion of bare ground did not differ due to grazing pressure, but the reduction in biomass lead to a less stratified vegetation cover.
