316 MICROBIOLOGICAL SOIL PROPERTIES OF THE FLOODPLAIN FORESTS NEAR GABČÍKOVO. I. POPLAR STANDS OLÍVIA ĎUGOVÁ, ALEXANDRA ŠIMONOVIČOVÁ Institute of Landscape Ecology of the Slovak Academy of Sciences, Štefánikova 3, P.O. Box 254, 814 99 Bratislava, Slovak Republic; e-mail: olivia.dugova@savba.sk Department of Pedology, Faculty of Natural Sciences, Comenius University, Mlynská dolina B2, 842 15 Bratislava, Slovak Republic Abstract Ďugová O., Šimonovičová A.: Microbiological soil properties of the floodplain forests near Gabčíkovo. I. poplar stands. Ekológia (Bratislava), Vol. 27, No. 3, p. 316–325, 2008. Microbiological analyses, establishment of biomass and biological activity of microbial com- munities in the monocultures of poplar stands were carried out. Their age moved from 10 to 40 years (T1–T4). The results show that microbial communities are less stable in variants T1–T2 than in variants T3–T4 (in the year 1994). The comparison of the years 2001–2005 showed that microbial communities are more stable and the differences between stands T1–T2 and T3–T4 are minimum. Key words: microbial biomass, biological activity, poplar stands Introduction Man and his activities cause positive or negative changes in the landscape and character of climate. Their result is also the endangerment of biodiversity of plant and animal commu- nities. Human influences on the pedosphere are more and more intensive. Many problems are of regional to global significance, e.g. amplification of the green-house effect, reduc- tion of the ozone layer, soil acidification, grubbing of rain forests, gradual aridation and desertification of the area, extent soil erosion etc. At present the existing floodplain forest ecosystems are only their remnants not only in Slovakia but in Europe, too. The pressure of man on floodplain forests and landscape near the rivers was intensive even in the past and it was continually increased. First of all water management measures, as e.g. building of flood control dams, drainage, amelioration, flood elimination etc., limited the area of floodplain forest to the minimum. In the 20 th century within these negative phenomena appeared also large change in tree species composition, Ekológia (Bratislava) Vol. 27, No. 3, p. 316–325, 2008