Effect of drought-rewetting cycles on the diversity and functioning of bacterial metacommunities

Background/Question/Methods

Drought-rewetting cycles are one of the most prevelant natural disturbance episodes of temporary water bodies that might change in frequency and intensity due to climate change. However, little is known about the ecological relevance of this process for bacterial diversity and function at the metacommunity scale. Hence the main purpose of this study was to address changes in taxonomic and functional alpha- and beta diversity and ecosystem functions in a bacterial metacommunity during the drying and re-wetting period. We hypothesize that droughts are harsh environmental stressors that will reduce taxonomic beta-diversity and lead to concomitant decreases in functional diversity and ecosystem process rates, and that dispersal has the potential to mitigate these effects. To test this we implemented an experimental study where sets of freshwater metacommunities consisting of 3 different patches were dried and rewetted under controlled conditions. Dispersal was applied before drying and after rewetting at an early and late stage of the community re-assembly process to test its effect on the compositional and functional resistance and resilience of the metacommunities. Respiration rates and functional diversity (measured as substrate utilization profiles using Biolog Ecoplates) and bacterial community diversity and composition (high throughput sequencing of the 16S rRNA gene) were measured at various time points before during the drying and rewetting period.

Results/Conclusions

Functional beta-diversity and respiration rates increased during the drying process. After rewetting, respiration remained altered compared to pre-drying values, substrate utilization profiles changed, beta-diversity decreased and shifts in the identity of dominant phyla were induced. Dispersal always lowered both taxonomic and functional beta-diversity but had no effect on respiration rates. Hence, there were no indications of rapid recovery to pre-disturbance conditions, neither in metacommunities with or without dispersal. Our results therefore show that drought-rewetting processes have significant effects on both the diversity and function of bacterial metacommunities and therefore need to be considered when the effects of climate change on aquatic ecosystems are evaluated.