PS 15-143 - Shifting habitat-use by arctic small mammals and effects on soil biogeochemical cycling

Background/Question/Methods

As structure builders, arctic small mammals have important effects on soil biogeochemical cycling and resulting influences on bottom-up regulation of arctic ecosystem function. However, shifts in their habitat-use due to climate change will likely alter the role they play in the Arctic. Our aim was to determine how brown lemming (Lemmus trimucronatus) structures and shifts in lemming distributions may alter tundra biogeochemical cycling. Specifically, we compared the impacts of brown lemming structures (nests, burrows, latrines, and runways) on soil nutrient cycling in traditional brown lemming habitat and in habitat currently dominated by collared lemmings (Dicrostonyx groenlandicus), into which brown lemmings may expand their range into due to climate change. We collected soil organic-layer samples beneath various brown lemming structures and control sites within each habitat and analyzed them for a variety of biogeochemical variables: soil inorganic nutrients (NH₄⁺, NO₃^-, PO₄^3-), extractable organic nutrients (EOC, ETN, EON), microbial biomass (MBC, MBN, MBP), and the activity of ten soil exo-enzymes (eight hydrolytic and two oxidative enzymes).

Results/Conclusions

The few effects we observed of brown lemming structures on soil nutrients were only observed within their traditional habitat. We found that soil from burrows had higher PO₄^3-, lower EOC, and a trend for lower MBC concentrations compared to control sites. These increases in soil PO₄^3- and decreases in soil C pools were likely due to reduced vegetation at burrow entrances. Differences in burrow effects between habitats may have important effects on biogeochemical processes. As tundra systems may show P limitation, increases in PO₄^3- may increase productivity at burrow-adjacent sites. Additionally, decreases in soil C at burrows suggest that burrows may represent areas of C loss from tundra ecosystems. Our findings suggests that the importance of brown lemming structures (e.g., burrows) in regulating nutrient availability will decrease as brown lemmings move into collared lemming habitats. Additionally, as burrows have generally long persistence times and can cover ca. 1% of the landscape, they may have long-term effects on tundra ecosystem function. We conclude that the difference in effects of structures between habitat types may have important feedbacks on biogeochemical cycling and ecosystem function if herbivore species adjust their habitat-use due to climate change.