Seasonal dynamics of CO2 exchange during primary succession of boreal mires as controlled by phenology of plants

Seasonal dynamics in vegetation and carbon dioxide (CO2) exchange were studied at 5 small mire basins along a chronosequence from the initial stages of paludification through to the bog stage in the Bay of Bothnia region in Finland. Precipitation and mean temperature during the summer 2004 study season were measured at a nearby meteorological station. Plant community composition was determined by estimating the projection cover of each species. Subplots in each of the study sites were established to count the number of living leaves of all vascular plant species. Sample plots were surrounded by aluminum collars in order to facilitate CO2 exchange measurements. Infrared gas analyzers were used to measure CO2 concentrations. Seasonal estimates of CO2 exchange dynamics were modelled in order to quantify the importance of different functional plant groups during the mire successions. Results of the study showed that seasonal variations in plant phenology and ecosystem respiration decreased in older sites along a mire chronosequence. Photosynthetically effective groups such as sedges and graminoids determined most of the seasonal CO2 dynamics. The higher level of gross photosynthesis combined with lower ecosystem respiration made the younger successional stages the largest sinks of atmospheric CO2. Results suggested that autogenic factors controlled both the level and variation of CO2 exchange during mire succession. It was concluded that changes in vegetation must be considered when developing dynamic carbon models for mires of different ages, peat depths, and successional stages. 61 refs., 3 tabs., 8 figs