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The microbial communities of lake sediments play key roles in carbon cycling, linking lakes to their surrounding landscapes and to the global climate system as incubators of terrestrial organic matter and emitters of greenhouse gasses, respectively. Here, we amended lake sediments with three different plant leaf litters: a coniferous forest mix, deciduous forest mix, cattails (Typha latifolia) and then examined the bacterial, fungal and methanogen community profiles and abundances. Polyphenols were found to correlate with changes in the bacterial, methanogen, and fungal communities; most notably dominance of fungi over bacteria as polyphenol levels increased with higher abundance of the white rot fungi Phlebia spp. Additionally, we saw a shift in the dominant orders of fermentative bacteria with increasing polyphenol levels, and differences in the dominant methanogen groups, with high CH4 production being more strongly associated with generalist groups of methanogens found at lower polyphenol levels. Our present study provides insights into and basis for future study on how shifting upland and wetland plant communities may influence anaerobic microbial communities and processes in lake sediments, and may alter the fate of terrestrial carbon entering inland waters.

The microbial communities of lake sediments play key roles in carbon cycling, linking lakes to their surrounding landscapes and to the global climate system as incubators of terrestrial organic matter and emitters of greenhouse gasses, respectively. Here, we amended lake sediments with three different plant leaf litters: a coniferous forest mix, deciduous forest mix, cattails (Typha latifolia) and then examined the bacterial, fungal and methanogen community profiles and abundances. Polyphenols were found to correlate with changes in the bacterial, methanogen, and fungal communities; most notably dominance of fungi over bacteria as polyphenol levels increased with higher abundance of the white rot fungi Phlebia spp. Additionally, we saw a shift in the dominant orders of fermentative bacteria with increasing polyphenol levels, and differences in the dominant methanogen groups, with high CH4 production being more strongly associated with generalist groups of methanogens found at lower polyphenol levels. Our present study provides insights into and basis for future study on how shifting upland and wetland plant communities may influence anaerobic microbial communities and processes in lake sediments, and may alter the fate of terrestrial carbon entering inland waters.

Shallow lake sediments harbor methanogen communities that are responsible for large amounts of CH(4) flux to the atmosphere. These communities play a major role in degrading in-fluxed terrestrial organic matter (t-OM)—much of which settles in shallow near-shore sediments. Little work has examined how sediment methanogens are affected by the quantity and quality of t-OM, and the physicochemical factors that shape their community. Here, we filled mesocosms with artificial lake sediments amended with different ratios and concentrations of coniferous and deciduous tree litter. We installed them in three boreal lakes near Sudbury, Canada that varied in trophic status and water clarity. We found that higher endogenous nutrient concentrations led to greater CH(4) production when sediment solar irradiance was similar, but high irradiance of sediments also led to higher CH(4) concentrations regardless of nutrient concentrations, possibly due to photooxidation of t-OM. Sediments with t-OM had overall higher CH(4) concentrations than controls that had no t-OM, but there were no significant differences in CH(4) concentrations with different t-OM compositions or increasing concentrations over 25%. Differences among lakes also explained variation in methanogen community structure, whereas t-OM treatments did not. Therefore, lake characteristics are important modulators of methanogen communities fueled by t-OM.