RESPONSE OF HETEROTROPHIC MICROBIAL COMMUNITIES TO AN ENVIRONMENTAL GRADIENT IN THE FLOODPLAIN OF MAPIRE RIVER, VENEZUELA

Abstract Soil physico-chemical characteristics of floodplains, particularly hydrology, influence microbiological activity. As such, each river floodplain system has a unique physico-chemical dynamic that in turn supports the microbial community. The Mapire River floodplain is a complex system in which seasonal flood pulses cause changes in the soil physico-chemical variables. We examined how these temporal and spatial differences are associated with the microbiological activity along a seasonally flooded gradient at the mouth of the Mapire River (Lower Orinoco, Venezuela). Soil samples were collected during three different seasons by a systematic sampling at 4 points of the gradient, defined by the intensity of flooding. The physico-chemical parameters of the soil were determined and related by the density and physiological profile of the microbial community through multivariate permutation analysis and gradient analysis. The results indicate that there is a spatial gradient determined by soil clay content and a temporal gradient influenced by moisture and total organic carbon. Significant differences were found among soil zones and seasons, with the interaction of both factors also significant. It was observed that microbial activity is decisive in phosphorus dynamics, even during flooding. It is concluded that amid the complex interactions between biotic and abiotic factors, microbial communities are able to respond to changes in the physico-chemical soil environment and maintain their activity throughout the hydroperiod.