| The effects of environmental perturbations on microbial community structure may strongly influence ecosystem functioning, as microorganisms play a dominant role in nutrient and carbon cycling. Vernal pools are an interesting model system for studying environmental effects on microbial structure and function, due to a physicochemical environment that is highly variable in space and time. In a field study, we found that changes in eukaryotic microbial communities of vernal pools were correlated with differences in a number of parameters, including dissolved oxygen, conductivity, urban land-use, and substrate quality. These results indicated that both landscape-level influences on vernal pool chemistry as well as local inputs of leaf litter are important for structuring microbial communities and further suggested that microbes may respond to multiple levels of environmental change.;In a microcosm study, we investigated the relationship between microbial community structure and function under different levels of environmental change: pH manipulation and nitrate (NO3-) addition. We found that bacterial and fungal communities were altered by pH, which corresponded with differences in respiration and suggested that broad changes can affect both structure and function. Denitrification, a microbial process which utilizes NO3- as an electron acceptor, was not detected in the absence of NO3-. This large change in function was independent of community structure hanges, as NO3- addition had little effect on community structure of bacteria, fungi, or denitrifying organisms or on denitrifier relative abundance or population size, indicating that narrow changes may not affect community dynamics, even of functional groups. The microbial communities in the microcosms were further characterized with a metagenomic approach, which showed no difference in bacterial richness or diversity with NO3- addition and reaffirmed previous conclusions that changes in denitrification could occur without altered microbial community structure. The metagenomes further revealed high metabolic diversity, suggesting that denitrifiers and other groups of vernal pool microbes may rely on physiological plasticity for growth when certain resources are limiting. Overall, our results suggest that microbial community stability and effects on function are highly context-dependent, driven by the nature of the environmental perturbation and the physiological plasticity of the communities affected. |
