Compositional and functional resilience to drought-rewetting events

Background/Question/Methods

Periods of drought and rewetting events are expected to increase in intensity with global climate change, however the implications for these changes on ecosystems are not well understood. As microbes are responsible for nutrient cycling, the effect of these events on microbial communities could be especially important. Examining the changes in microbial community composition and function that occur before, during and after a period of drought will help us to understand the role that resistance, resilience, and functional redundancy play in the microbial community response. In order to characterize the microbial response to drought and rewetting in situ, soil samples were collected monthly in a mixed hardwood forest over a growing season that included a mid-summer drought period, followed by a period of rewetting. DNA fingerprinting techniques and carbon substrate utilization patterns were used to characterize soil microbial community composition and function, respectively. Soil respiration and inorganic nitrogen were measured so that changes in soil nitrogen and microbial activity could be correlated to aspects of environmental and community change.  

Results/Conclusions

Drought reduced microbial activity. Drought also changed the pattern of utilization of different carbon substrates, but carbon utilization eventually returned to the pre-drought pattern. Thus, microbial communities showed functional resilience to drought disturbance. The composition of the soil microbial community changed greatly in the rewetting period immediately following the drought, but eventually microbial community composition recovered to the pre-drought state. This indicates that community composition is also resilient to drought-rewetting events. Overall, results document change in function and composition that occurs during drought and rewetting periods, and indicate a role for functional and compositional resilience in maintaining ecosystem function following drying and rewetting events.