Are lemmings driving carbon sequestration in arctic ecosystems?
A delicate balance determines the sink or source character of soils.
Soils may either serve as a sink or as a source for carbon dioxide. They are sinks, when the formation of organic matter by plants dominates. The preponderance of microbial degradation of soil organic matters results in liberation of carbon dioxide; soils then become sources of carbon dioxide. The balance between deposition and decomposition is fragile and depends on many factors like insolation, albedo, temperature, carbon dioxide levels and so forth.
In the long term lemmings support the sink character of soils.
Lara and colleagues studied one of these factors in detail: herbivory. They took advantage of a long-term experiment in the high Arctic, where lemmings had been excluded from specific areas for more than 50 years. In contrast to other, short-term experiment, their data demonstrate that the absence of lemmings can strengthen the source character of soils. Results were particularly significant for the wet tundra, where soils turned from sink to source in the peak growing season. Given the apparent decline of lemming numbers in the Arctic, these results indicate the existence of a further factor afflicting carbon balances in the decades to come.