THE MICROBIAL LOOP AT THE SURFACE OF A PEATLAND - STRUCTURE, FUNCTION, AND IMPACT OF NUTRIENT INPUT

The aim of this study was to assess the structure and function of the microbial loop in a peatland of the French Massif central, and the imp act of fertilization on the different microbial communities. In terms of biomass, testate Amoeba (48% of the total microbial biomass), heter otrophic bacteria (15%), cyanobacteria (14%) and Bacillariophyceae (13 %) were the dominant groups of microorganisms. Other microalgae (7%), ciliates (2%) and heterotrophic flagellates (1%) accounted for only a low proportion of total microbial biomass. The relative importance of heterotrophic microorganisms was higher than in marine or lacustrine e nvironments. In addition, ciliates and heterotrophic flagellates only constituted a small proportion of the total protozoan biomass, which w as heavily dominated by testate amoeba. Thus, the structure of the pro tist community in the subaquatic peatland was completely different fro m that reported for lakes or marine environments. In other aspects, th e supply of nutrients (PKCa and NPKCa) resulted in increases of the re lative biomasses of heterotrophic bacteria, Bacillariophyceae, and cil iates and by a decrease in the relative proportion of testate amoeba a nd of other microalgae.