Do earthworm and litter inputs promote decomposition or stabilization of cryoturnated organic matter from melted permafrost?

As global climate change progresses, Artic permafrost melts. Deeper layers of permafrost contain organic matter which can migrate into deeper soil by a process called cryoturbation. While this organic matter does not decompose in frozen soils, it decomposes rapidly in melting permafrost. Warming soils may experience increased litter input and earthworm colonization. The effects of litter addition and earthworm colonization on the decomposition and condition of permafrost remain unclear. This study used laboratory experiments to compare effects of willow litter (Salix caprea) addition and earthworm activity (Aporectodea caliginosa) on cryogenic organic matterfrom permafrost soils mixed in mineral soil and mineral soil itself. Respiration and stability of organic matter was monitored over two years with new litter added three times once litter in the soil with earthworms had disappeared from the soil surface. After a two-year period, treatments with litter addition and with earthworms alone showed increased system respiration, but effects were non-cumulative. The soil samples receiving earthworms showed higher proportions of organic matter stabilized in the mineral fraction by the end of the experiment. These preliminary lab results suggest that litter supply and earthworm colonization may both stabilize and speed up mineralization of organic matter released from melting permafrost.