Experimental Warming Alters Productivity and Isotopic Signatures of Tundra Mosses

In the tundra, mosses play an important functional role regulating belowground and ecosystem processes, but there is still considerable uncertainty about how tundra moss communities will respond to climate change. We examined the effects of 5 years of in situ air and soil warming on net primary productivity (NPP), carbon (C) and nitrogen (N) isotope signatures (δ¹³C and δ¹⁵N), and C:N in dominant Alaskan tundra mosses. Air warming increased mean air temperatures by up to 0.5°C and resulted in an 80–90% reduction in NPP in the feather moss Pleurozium and the peat moss Sphagnum. Soil warming increased permafrost thaw depth by 12–18%, upper soil water content by 23–27%, and resulted in a threefold increase in Sphagnum NPP. δ¹³C was positively correlated with moss NPP, and increased by 0.5–1‰ in all mosses under soil warming. C:N was reduced in Sphagnum and Pleurozium, due to increases in tissue %N in the soil warming treatment, suggesting that moss N availability could increase as temperatures increases. Higher N availability in warmer conditions, however, may be offset by unfavorable moisture conditions for moss growth. Similar to responses in tundra vascular plant communities, our results forecast interspecific differences in productivity among tundra mosses. Specifically, air warming may reduce productivity in Sphagnum and Pleurozium, but soil warming could offset this response in Sphagnum. Such responses may lead to changes in tundra moss community structure and function as temperatures increase that have the potential to alter tundra C and N cycling in a future climate.