Nitrogen cycling and the spread of shrubs control changes in the carbon balance of arctic tundra ecosystems

Decomposition in the Arctic has been slower than plant growth, causing an accumulation of detritus in tundra soils. Climate warming may result in carbon (C) loss by accelerating the decomposition of soil organic matter (SOM). Nitrogen (N) release from SOM may also enhance plant growth, which is limited by N availability in tundra ecosystems. Since N acquisition varies by plant species, changes in plant community composition resulting from climate change may alter carbon cycling in tundra soils. Shrubs are growing in predominance in tundra communities in response to warming. Since they are the woodiest plants in the tundra, this may increase ecosystem C storage, because wood has the highest C:N ratio of any plant tissue and decomposes slowly. Whether net ecosystem C storage increases or decreases will depend on the balance of (a) C losses from SOM and (b) C storage in plant pools due to higher primary productivity and changes in plant community composition.