Abstract
(Englisch)
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The primary objective of the 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. These objectives further include the quantification of the impact of elevated CO2 and N, specifically: 1) on the population dynamics of different species of peatmoss and selected vascular plants; 2) on the growth of dominant species in the bog ecosystem; 3) on the organochemical and structural properties of dominant mire plants; 4) on the decomposability of litter from mire plants; and 5) on the emission of CH4 from the bogs. Quantification will facilitate the objective to develop process-oriented models that describe responses of botanical composition, C-sequestration and CH4 emission in bogs in Europe in response to possible scenarios of future changes in atmospheric CO2 , N deposition and climate.
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.
The following five Sphagnum bog research sites were selected for BERI: 1) Sweden, Kopparasmyren, 2) Finland, Salmisuo in Ilomantsi, 3) United Kingdom, The Migneint, NorthWales, 4) The Netherlands, Peat from Dwingelo transplanted to Wageningen, 5) Switzerland, Les Chaux-des-Breuleux.
The field research takes place in ombrotrophic lawn communities (S. magellanicum, S.balticum, or S. papillosum) and associated vascular plants. At each site the following four treatments are replicated five times: elevated atmospheric CO2 (target concentration 560 ppm) in Mini-FACE rings; ambient CO2 controls: Mini-FACE rings that vent ambient air; small (2-3 m2) plots receiving extraNitrogen, weekly NH4NO3 (5 g N m-2yr-1); control N-plots receiving a similar volume of distilled water.
Each Mini-FACE ring consists of a circular (1.0 m ) arrangement of about 70 venting pipes that blow CO2 -enriched air. An IR gas analyzer and PC maintain a target CO2 concentration of 560 ppm after mixing with ambient air inside the ring. The measurement program includes, as core protocols, the following: abundance of species and relative cover by the 'point quadrats' method; primary production by a modified 'cranked-wire' method; litter bag decomposition experiments; 14C labelling 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 and environmental variables. Supplementary protocols are: 1) Effects of CO2 and N elevation on the testaceans assemblage (Protozoa; Rhizopoda) and 2) Biomass allocation of Eriophorum vaginatum seedlings under the different treatments. A simulation model will be developed to test the hypotheses and to account for the different climates. The ultimate aim is to describe relevant processes in a deterministic model, so that the effects of different global change scenarios can be evaluated.
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