Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 12 1 2008 10.5194/hess-12-277-2008 http://www.hydrol-earth-syst-sci.net/12/277/2008/ http://www.hydrol-earth-syst-sci.net/12/277/2008/hess-12-277-2008.html http://www.hydrol-earth-syst-sci.net/12/277/2008/hess-12-277-2008.pdf 277 291 2008-02-26 Vegetation composition and soil microbial community structural changes along a wetland hydrological gradient W. K. Balasooriya wajira.balasooriya@ugent.be K. Denef J. Peters N. E. C. Verhoest P. Boeckx Department of Forest and Water Management, Ghent University, Coupure links 653, 9000 Gent, Belgium Department of Applied Analytical and Physical Chemistry, Ghent University, Coupure links 653, 9000 Gent, Belgium Fluctuations in wetland hydrology create an interplay between aerobic and anaerobic conditions, controlling vegetation composition and microbial community structure and activity in wetland soils. In this study, we investigated the vegetation composition and microbial community structural and functional changes along a wetland hydrological gradient. Two different vegetation communities were distinguished along the hydrological gradient; Caricetum gracilis at the wet depression and Arrhenatheretum elatioris at the drier upper site. Microbial community structural changes were studied by a combined in situ 13CO2 pulse labeling and phospholipid fatty acid (PLFA) based stable isotope probing approach, which identifies the microbial groups actively involved in assimilation of newly photosynthesized, root-derived C in the rhizosphere soils. Gram negative bacterial communities were relatively more abundant in the surface soils of the drier upper site than in the surface soils of the wetter lower site, while the lower site and the deeper soil layers were relatively more inhabited by gram positive bacterial communities. 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