Marcel R. Hoosbeek1 (firstname.lastname@example.org), Nico Van Breemen1,
Bo Wallen2, Hakan Rydin3, John A. Lee4, Jouko Silvola5, Harri Vasander6,
Frank Berendse7, Edwin Van Der Heijden8 & Philippe Grosvernier9
1 Dept. of Soil Science and Geology, Wageningen Agricultural University, The Netherlands.
2 Department of Plant Ecology, Lund University, Sweden.
3 Department of Ecological Botany, Upsala University, Sweden.
4 Department of Environmental Biology, University of Sheffield, United Kingdom.
5 Department of Biology, University of Joensuu, Finland.
6 Department of Forest Ecology, University of Helsinki, Finland.
7 Dept. of Terrestrial Ecology and Nature Mgmt, Wageningen Agricultural University, The Netherlands.
8 Department of Plant Biology, University of Groningen, The Netherlands.
9 Laboratory for Plant Ecology and Phytosociology, University of Neuchâtel, Switzerland.
The primary objective of the Bog Ecosystem Research Initiative (BERI) project is to study, at five climatically different sites across Europe, the effects of elevated CO2 and N deposition on the net exchange of CO2 and CH4 between bogs and the atmosphere. Secondly, to study the effects of elevated CO2 and N deposition on the plant biodiversity of bog communities.
We hypothesize that even in a nutrient-poor bog environment, elevated CO2 will stimulate plant growth. We expect growth of Sphagnum to be stimulated more than that of vascular plants because increased growth lowers N availability, which affects vascular plants more than Sphagnum. For the same reason, Sphagnum of hummocks will expand at the cost of Sphagnum at hollows. Increased peat growth positively feeds back to Sphagnum itself, but further depresses vascular plants. This sequence of events forms a strong negative feed back of increased sequestration of CO2-C. Increased CO2 would increase CH4 emissions in the short run where peat expands over non-wetland soils. However, it would decrease CH4 emissions in the long run if it stimulates formation of hummocks in existing peats.
Ombrotrophic lawn communities (S. magellanicum, S.balticum, or S. papillosum) and associated vascular plants were sampled at five sites across Europe, and the following four treatments are replicated five times: (1) Elevated atmospheric CO2 (target concentration 560 ppm) in Mini-FACE rings, (2) Ambient CO2 controls: Mini-FACE rings that vent ambient air, (3) Small (2-3 m2) plots receiving extra Nitrogen, weekly NH4NO3 (5 g N m-2 yr-1), and (4) Control N-plots receiving a similar volume of distilled water.
The measurement programme includes the following: abundance of species and relative cover by the "point quadrants" method; primary production by a modified "cranked-wire" method; 14C labeling techniques; biweekly CH4 fluxes; net exchange of CO2 in Finland; organo-chemical and structural changes in Sphagnum due to treatments; and a suite of climatic variables.
At this time only some preliminary results of the first field season and from greenhouse experiments are available. In Finland, Sweden and The Netherlands the elevated CO2 treatment resulted in increased CH4 emissions. The influence of elevated CO2 on Sphagnum is not clear yet: in Sweden and The Netherlands an increase in Sphagnum length growth was observed under elevated CO2, while in the U.K. and Switzerland a relative reduction was observed. However, Sphagnum shoot density increased under elevated CO2 in Sweden and Switzerland, while no effect was observed in the U.K. and The Netherlands.
Earlier growth chamber experiments by the Finnish group suggested that the effect of elevated CO2 on methane emission depends very much on temperature and might be quite small in boreal cool conditions. To identify the possible small effects, CH4 emission was measured 1 to 2 times per week. Elevated CO2 stimulated CH4 emission within a few weeks after the start of the treatment. The increase was about 20 % in the middle of the growing season. In a cold period (weeks 27-31) the effect of CO2 disappeared, but it appeared again in the following warmer period. In cold and dry conditions the effect disappeared again in autumn (weeks 38-42), but came back when heavy rains had raised the water level. In the N-treatment and control plots this seasonal rhythm is very similar, but the effect of added N was not clear during the first year.
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