Abstract
Northern permafrost soils contain important carbon stocks. Here we report the long-term response of carbon stocks in high Arctic dwarf shrub tundra to short-term, low-level nutrient enrichment. Twenty years after experimental nitrogen addition, carbon stocks in vegetation and organic soil had almost halved. In contrast, where phosphorus was added with nitrogen, carbon storage increased by more than 50%. These responses were explained by changes in the depths of the moss and organic soil layers. Nitrogen apparently stimulated decomposition, reducing carbon stocks, whilst phosphorus and nitrogen co-stimulated moss productivity, increasing organic matter accumulation. The altered structure of moss and soil layers changed soil thermal regimes, which may further influence decomposition of soil carbon. If climate warming increases phosphorus availability, any increases in nitrogen enrichment from soil warming or expanding human activity in the Arctic may result in increased carbon sequestration. Where phosphorus is limiting in tundra areas, however, nitrogen enrichment may result in carbon loss.
Highlights
It is well established that metabolic processes in Arctic plants and soils are often nutrient limited, by nitrogen (N) or by N and phosphorus (P)
The changes in the depth of the moss and soil layers were the primary drivers of C stock responses to nutrient treatments, with 99% of the variation in total organic carbon stocks across treatments being explained by the combined depth of the two layers (Figure 1B)
This study demonstrates that short-term N enrichment of high Arctic dwarf shrub tundra has a longterm influence on ecosystem C stocks, with the outcome depending on P availability
Summary
It is well established that metabolic processes in Arctic plants and soils are often nutrient limited, by nitrogen (N) or by N and phosphorus (P) (for example, Shaver and Chapin 1995). Potential increases in the availability of nutrients, whether through anthropogenic inputs or soil warming, may result in increased vegetation productivity (Shaver and Chapin 1995) and/or increased microbial activity and soil organic matter (SOM) decomposition (Hartley and others 2010). The balance between plant growth and SOM decay largely determines net C storage, which in the Arctic has global significance. It is imperative that we understand how the processes governing ecosystem C balance respond to nutrient availability, as these processes will be critical in determining the global impact of rapid Arctic climate change
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