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

Abstract

The effect of elevated UV-B radiation on CO 2 exchange of a natural flark fen was studied in open-field conditions during [2003][2004][2005]. The experimental site was located in Sodankylä in northern Finland (67122 0 N, 26138 0 E, 179 m a.s.l.). Altogether 30 study plots, each 120 cm  120 cm in size, were randomly distributed between three treatments (n 5 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 2 exchange (NEE) and dark respiration (R TOT ) were measured during the growing season using a closed chamber method. The wintertime CO 2 emissions were estimated using a gradient technique by analyzing the CO 2 concentration in the snow pack. In addition to the instantaneous CO 2 exchange, the seasonal CO 2 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 R TOT was significantly lower under elevated UV-B in the third study year. The modeled seasonal (June-September) CO 2 balance varied between the years depending on the ground water level and temperature conditions. During the driest year, the seasonal CO 2 balance was negative (net release of CO 2 ) in the ambient control and the UV-B treatment was CO 2 neutral. During the third year, the seasonal CO 2 uptake was 43 AE 36 g CO 2 -C m À2 in the ambient control and 79 AE 45 g CO 2 -C m À2 in the UV-B treatment. The results suggest that the long-term exposure to high UV-B radiation levels may slightly increase the CO 2 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 2 balance of fen ecosystems in future.

Plant‐mediated effects of elevated ultraviolet‐B radiation on peat microbial communities of a subarctic mire

“…Lower carbohydrate content or extractability, among other UV‐induced changes in litter quality, have been observed to reduce the decay rate (Gehrke et al , 1995; Pancotto et al , 2005) or to accelerate it, possibly due to an altered decomposer community (McLeod et al , 2007). Field measurements over the growing seasons 2003–2005 at the peatland site of the present work have shown that elevated UVB radiation significantly decreased dark ecosystem respiration, possibly due to slower decomposition processes and microbial respiration (Haapala et al , submitted). Based on the results of the present paper, we suggest that the reduced respiration owed partly to the lower bacterial growth rate and partly to the possibly slower litter decay rate due to altered tissue quality.…”

Supplemental UV‐B induced changes in leaf morphology, physiology and secondary metabolites of an Indian aromatic plantCymbopogon citratus(D.C.) Staph under natural field conditions

“…Relying on the work of the Goddard Institute for Space Studies (GISS), Finnish researchers have estimated that relative to conditions from 1979 to 1992, in the Northern Hemispheric zone (Russia, China, India, Sri Lanka) the maximum increase in the annual UV dose would be 14% in 2010-2020, but there would be a 40% enhancement for the same period in the Southern Hemisphere (Brazil) [75][76][77]. So, the UV-B level in the lemongrass producer countries is predicted to rise in the near future.…”

Effects of UVB radiation on freshwater biota: a meta‐analysis

“…This implies that UVB, as one of the main global change factors, could result in a decline, or even the extinction, of some freshwater species. The Goddard Institute for Space Studies (GISS) predicted that the maximum increase in the annual Northern Hemispheric UVB dose will be 14% in 2010-20, while a 40% enhancement is expected in the Southern Hemisphere, compared with conditions from 1979-92 (Haapala et al, 2009). Hence, the underlying threats to freshwater organisms, especially to zooplankton, maybe further aggravated with the continuous increases in UVB in the future.…”