Dispersal timing and drought history influence the response of bacterioplankton to drying-rewetting stress

The extent and frequency of drought episodes is expected to increase in the following decades making it a crucial stress factor for smaller water bodies. However, very little is known about how bacterioplankton is affected by increased evaporation and how these communities re-assemble after rewetting. Here we present results from a microcosm experiment that assessed the effect of drying-rewetting stress on bacterioplankton in dependence of the stress history and the rate and timing of dispersal after the rewetting. We found that the drying phase generated primarily functional responses, while the complete desiccation and rewetting processes strongly affected both composition and function, which were, however, dependent on the initial conditions and stress history of the communities. Effects of dispersal were generally stronger when it occurred at an early stage after the rewetting. At this stage selective establishment of dispersed bacteria coupled with enhanced compositional and functional recovery was found, whereas effects of dispersal were neutral, i.e. predictable by dispersal rates, at later stages. Our studies therefore show that both the stress history and the timing of dispersal are important factors that influence response of bacterial communities to environmental change and stress events.