How beavers are changing Arctic pond and stream microbiology

Findings indicate that bacteria and archaea found in Arctic beaver ponds are different from those of tundra lakes and streams. Beaver ponds may provide favorable conditions for plant-associated fungi, while tundra lakes and streams display particularly high relative abundances of fungal parasites.

The North American beaver has moved into tundra regions of Alaska in recent decades as a result of more favorable habitat and population rebound from overtrapping in previous centuries. On the tundra, beavers create/engineer ponds, changing how water flows, carbon and nutrient cycling, and the rate of permafrost thawing. Our study compares the microbiology of Alaskan tundra beaver pond sediments to that of pristine tundra lakes and streams in an Arctic region still undisturbed by beavers. Our findings indicate that bacteria and archaea found in Arctic beaver ponds are different from those of tundra lakes and streams, yet dominant fungal lineages were not different between these settings. Based on the types of microbes found, beaver ponds may provide favorable conditions for plant-associated fungi, nitrogen- and sulfur-cycling bacteria, and aerobic bacteria, while tundra lakes and streams display particularly high relative abundances of fungal parasites and pathogens and anaerobic bacteria and archaea that are usually attributed with fermentative, methanogenic, and syntrophic or cooperative metabolisms. Our data provides a first look at the microbiology of far northern beaver ponds, an ecological setting that's unique to a drastically changing Arctic.

Also see: Beavers Are Remaking Microbial Ecosystems in the Arctic - Eos

Comparing sediment microbial communities of Arctic beaver ponds to tundra lakes and streams

Abstract

In recent decades the habitat of North American beaver (Castor canadensis) has expanded from boreal forests into Arctic tundra ecosystems. Beaver ponds in Arctic watersheds are known to alter stream biogeochemistry, which is likely coupled with changes in the activity and composition of microbial communities inhabiting beaver pond sediments. We investigated bacterial, archaeal, and fungal communities in beaver pond sediments along tundra streams in northwestern Alaska (AK), USA and compared them to those of tundra lakes and streams in north-central Alaska that are unimpacted by beavers. β-glucosidase activity assays indicated higher cellulose degradation potential in beaver ponds than in unimpacted streams and lakes within a watershed absent of beavers. Beta diversity analyses showed that dominant lineages of bacteria and archaea in beaver ponds differed from those in tundra lakes and streams, but dominant fungal lineages did not differ between these sample types. Beaver pond sediments displayed lower relative abundances of Crenarchaeota and Euryarchaeota archaea and of bacteria from typically anaerobic taxonomic groups, suggesting differences in rates of fermentative organic matter (OM) breakdown, syntrophy, and methane generation. Beaver ponds also displayed low relative abundances of Chytridiomycota (putative non-symbiotic) fungi and high relative abundances of ectomycorrhizal (plant symbionts) Basidiomycota fungi, suggesting differences in the occurrence of plant and fungi mutualistic interactions. Beaver ponds also featured microbes with taxonomic identities typically associated with the cycling of nitrogen and sulfur compounds in higher relative abundances than tundra lakes and streams. These findings help clarify the microbiological implications of beavers expanding into high-latitude regions.

Shannon, K. C., N. R. Christman, B. C. Crump, M. P. Carey, J. Koch, L. L. Lapham, J. A. O'Donnell, B. A. Poulin, K. D. Tape, J. A. Clark, and F. S. Colwell. 2023. Comparing sediment microbial communities of Arctic beaver ponds to tundra lakes and streams. JGR Biogeosciences 128(8): e2023JG007408.