Arctic herbivorous rodents play an important role in determining ecosystem function by acting as ecosystem engineers and altering soil nutrients. The degree of impact of these herbivores on soil nutrient cycles likely varies by the different types of activity displayed by the herbivore. Our aim was to determine how herbivorous rodents affect arctic nutrient cycling. Our specific goal was to examine the influence of different activity types on CNP concentrations in soils. We examined the impact of four brown lemming (Lemmus trimucronatus) activities (nests, latrines, runways, and burrows) on soil nutrient pools. We predicted that soils from nests, latrines, and runways would have increased nitrogen (N) concentrations compared to control sites, while burrows and latrines would have increased phosphorus (P) concentrations. We collected organic soil samples from immediately below each lemming activity type and analyzed them for inorganic nutrients (NH4+, NO3-, PO43-), extractable organic nutrients (EOC, ETN, EOP), microbial biomass (MBC, MBN, MBP), and exo-enzyme activity (eight hydrolytic and two oxidative enzymes).
Results/Conclusions
Lemming activities had the strongest influences on N pools. Nests in particular had increased NH4+, Extractable Total N, and microbial biomass N compared to control plots. Other activity types also affected soil N including increased NH4+ in burrows and higher Extractable Total N in runways and burrows than non-disturbed controls. Additionally, nests and runways showed higher soil C pools compared to controls including higher Extractable Organic C (EOC) and Total % C under nests, and higher EOC under runways. In contrast, we observed no effect of lemming activity on soil P pools.
We conclude that individual activities of herbivores alter nutrient availability in different ways and may regulate nutrient limitation at different scales, from local impacts (runways and burrows) to nutrient transport and concentration on the landscape (nests). The influence of different activities may also vary in duration by having persistent effects (nests) or making nutrients rapidly available (latrines) for use by plants and microbes. Furthermore, our data suggest that while rodent activities may not alter the size of the microbial biomass, they do alter its stoichiometry. The importance of arctic rodents on ecosystem function is likely to vary during different phases of their population cycle, and their indirect effects on the environment may influence ecosystem processes across seasons and years.