The response of vernal pool microbial communities to environmental fluctuation and land-use patterns

Background/Question/Methods Vernal pools are seasonally flooded water bodies found in many temperate forest ecosystems.  Vernal pools are spatially and temporally dynamic over short periods of time, and may be particularly sensitive to global change phenomenon (e.g., nitrogen deposition, global warming, urban expansion).  In addition, vernal pools may represent significant sites of ecosystem element cycling and energy flow in the forest ecosystem due to microbial processing of allocthonous leaf litter inputs, which affects the resource base of more complex organisms that rely on these habitats.  Consequently, new studies are needed to improve our understanding of the link between environmental processes and microorganisms in these habitats and to better evaluate the functional role of vernal pools at the ecosystem and landscape scale. In a field study, links between eukaryotic microbial community composition and environmental parameters were investigated in 30 vernal pools of the Cuyahoga River watershed.  The environmental parameters measured were pH, dissolved oxygen, temperature, conductivity, depth, and a variety of land-uses of surrounding sub-watersheds (n= 3 pools per sub-watershed).  The eukaryotic microbial community was profiled with Denaturing Gradient Gel Electrophoresis (DGGE) and these profiles were compared between pools using nonmetric multidimensional scaling (NMS). 

Results/Conclusions DGGE revealed 47 operational taxonomic units, of which, 45 were subjected to DNA sequencing.  Of the 45 recovered sequences, 40% matched with fungal species, specifically the groups Ascomycota, Basidiomycota, and Chytridiomycota; 27% matched with protist species, specifically the groups Alveolata, Cercozoa, and Amoebozoa; and 24% matched with algal species, specifically the groups Bacillariophyceae, Chrysophyceae, Synurophyceae, and Xanthophyceae.  The NMS comparison revealed that the eukaryotic community structure was correlated with the water quality parameters of conductivity, temperature, and depth (Pearson correlation coefficients of 0.444, 0.383, and -0.299, respectively, between the parameters and one of the NMS dimensions).  The community structure was also correlated with the percent of the sub-watersheds that was agricultural, urban, or natural land (Pearson correlation coefficients of -0.506, 0.419, and -0.328, respectively, between the land-uses and one of the NMS dimensions).  These results suggest that the eukaryotic microbes of vernal pools are influenced by a variety of interrelated factors of the surrounding landscape.  Further, the predominance of fungal taxa suggests that vernal pool eukaryotic communities are dominated by heterotrophic organisms and may be important sites of nutrient and carbon cycling.