Vegetation composition and soil microbial community structural changes along a wetland hydrological gradient

摘要

Fluctuations in wetland hydrology create an interplay between aerobic andanaerobic conditions, controlling vegetation composition and microbialcommunity structure and activity in wetland soils. In this study, weinvestigated the vegetation composition and microbial community structuraland functional changes along a wetland hydrological gradient. Two differentvegetation communities were distinguished along the hydrological gradient;Caricetum gracilis at the wet depression and Arrhenatheretumelatioris at the drier upper site. Microbial community structural changeswere studied by a combined in situ 13CO₂ pulse labeling andphospholipid fatty acid (PLFA) based stable isotope probing approach, whichidentifies the microbial groups actively involved in assimilation of newlyphotosynthesized, root-derived C in the rhizosphere soils. Gram negativebacterial communities were relatively more abundant in the surface soils ofthe drier upper site than in the surface soils of the wetter lower site,while the lower site and the deeper soil layers were relatively moreinhabited by gram positive bacterial communities. Despite their largeabundance, the metabolically active proportion of gram positive bacterial andactinomycetes communities was much smaller at both sites, compared to that ofthe gram negative bacterial and fungal communities. This suggests much slowerassimilation of root-derived C by gram positive and actinomycetes communitiesthan by gram negative bacteria and fungi at both sites. Ground water depthshowed a significant effect on the relative abundance of several microbialcommunities. Relative abundance of gram negative bacteria significantlydecreased with increasing ground water depth while the relative abundance ofgram positive bacteria and actinomycetes at the surface layer increased withincreasing ground water depth.