PARENT SESSION
Contributed Oral Session 121: Freshwater Wetlands
Thursday, August 11, 8:00 AM - 11:30 AM, Meeting Room 520 C, Level 5, Palais des congrès de Montréal
Successional change in seasonal dynamics of photosynthesis during primary paludification.
Hietala, Mirva *,1, Laine, Jukka 2, Tuittila, Eeva-Stiina3, 1 The Finnish Forest Research Institute, Muhos2 The Finnish Forest Research Institute, Parkano3 University of Helsinki, Helsinki
ABSTRACT- Mire succession from fen to ombrotrophic bog includes gradual change in vegetation composition. Typically grasses and sedges dominate the early stages of mire succession, while the abundance of mosses and shrubs increases during the succession. The phenological variation in the photosynthesis of grasses and sedges is partly controlled by inherited autogenic factors in addition to climatic control. Instead, the seasonal variation in the photosynthesis of evergreen shrubs and mosses is mainly influenced by the climatic factors. The aim of the study was to link the successional replacement of different functional plant groups to the change in seasonal variation of mire carbon fixation. We postulated that a shift from grass and sedge dominance to arboreal leads to more moderate seasonal variation in carbon fixation. In order to test our postulate, we studied vascular plant phenology and gross photosynthesis over a growing season in five mires that form a chronosequence at a land-uplift coast of Bothnian Bay, Finland. The youngest sites (ages appr. 100 and 150 yrs) are meadow like and dominated by Carex nigra, Agrostis canina and Warnstorfia exannulata. The intermediate sites (appr. 500 and 1065 ± 70 yrs) are fens which are dominated by Carex chordorrhiza and Sphagnum. The oldest site (age 2520 ± 50 yrs) is in transition phase from fen to bog. The vegetation is characterized by Sphagnum and shrubs (Empetrum nigrum, Vaccinium oxycoccos). The peat depth of the sites ranges between 0.1 to almost two meters. All of the sites have 6-10 sample plots that cover the variation in moisture and vegetation characteristic to each site. The dominance of grasses and sedges decreases from the young mires towards older ones. Along the gradient there was a decrease in the strength of seasonal variation in plant community, measured as leaf area dynamics. Our preliminary results supported the postulate: the seasonal variation in photosynthesis became more moderate with the increasing successional stage. ±
Key words: succession, paludification, photosynthesis, peatland