Carbon dioxide balance of a fen ecosystem in northern Finland under elevated UV-B radiation

摘要

The effect of elevated UV-B radiation on CO exchange of a natural flark fen was studied in open-field conditions during 2003-2005. The experimental site was located in SodankylcT in northern Finland (67p22'N, 26p38'E, 179 m a.s.l.). Altogether 30 study plots, each 120 cm x 120 cm in size, were randomly distributed between three treatments (n=10): ambient control, UV-A control and UV-B treatment. The UV-B-treated plots were exposed to elevated UV-B radiation level for three growing seasons. The instantaneous net ecosystem CO exchange (NEE) and dark respiration (RTOT) were measured during the growing season using a closed chamber method. The wintertime CO emissions were estimated using a gradient technique by analyzing the CO concentration in the snow pack. In addition to the instantaneous CO exchange, the seasonal CO balances during the growing seasons were modeled using environmental data measured at the site. In general, the instantaneous NEE at light saturation was slightly higher in the UV-B treatment compared with the ambient control, but the gross photosynthesis was unaffected by the exposure. The RTOT was significantly lower under elevated UV-B in the third study year. The modeled seasonal (June-September) CO balance varied between the years depending on the ground water level and temperature conditions. During the driest year, the seasonal CO balance was negative (net release of CO) in the ambient control and the UV-B treatment was CO neutral. During the third year, the seasonal CO uptake was 43pl36 g CO-C mpo in the ambient control and 79pl45 g CO-C mpo in the UV-B treatment. The results suggest that the long-term exposure to high UV-B radiation levels may slightly increase the CO accumulation to fens resulting from a decrease in microbial activity in peat. However, it is unlikely that the predicted development of the level of UV-B radiation would significantly affect the CO balance of fen ecosystems in future.