Soil bacterial communities and ecosystem functioning change more strongly with season than habitat in a restored floodplain

- Dynamic floodplains offer an ideal setting to study soil bacterial communities.
- We test the idea that soil bacterial communities change with space and time.
- The seasonal variability was substantially higher than the habitat variability.
- The ratio of seasonal vs. habitat variability decreased from the most dynamic to the most stable habitat.

Soil bacterial community structures and associated ecosystem functions are known to vary both in space and time but spatial and temporal patterns are rarely studied simultaneously. Dynamic floodplains offer an ideal setting to study these spatio-temporal patterns and to determine the relative importance of habitat diversity and seasons in shaping soil bacterial communities.We studied the differences between habitats and seasonal patterns of soil bacterial communities (T-RFLPs) and soil environmental conditions (temperature, moisture and time elapsed since last inundation) and ecosystem functioning proxies (basal respiration, enzymatic activity, microbial C and N) over one year in seven habitats of a restored floodplain.Soil bacterial community structures in the two habitats closest to the river were most divergent from the others. However, although bacterial community structures differed between habitats at all sampling times, their seasonal variability was substantially higher than the habitat differences. Most of the ecosystem functioning proxies were lowest in the most dynamic habitat (gravel bar). Furthermore, while both bacterial community structure and ecosystem functions varied in relation to environmental conditions, the two were not directly correlated, and the link between communities and functions was seasonally inconsistent. The ratio of seasonal vs. habitat variability of soil bacterial communities decreased from the most dynamic to the most stable (forest) habitat. Thus in dynamic ecosystems such as floodplains also external factors (flood disturbance, seasonally changing climatic conditions) might influence ecosystem functions and bacterial communities independently - possibly because of species functional redundancy - and are keys in maintaining floodplain taxonomical and functional diversity.