Soil and plant CO ₂ emission in response to variations in soil moisture and temperature and to amendment with nitrogen, phosphorus, and carbon in northern Scandinavia

High-latitude ecosystems contain large soil carbon stocks. Climate change scenarios predict higher temperatures and changed precipitation pattern in the Arctic, which is likely to alter the ecosystem carbon (C) balance. With few exceptions most studies of the ecosystem C balance in the Arctic have taken place in wet ecosystems, and it has been shown that the CO ₂ efflux is likely to increase if the moisture level declines. However, large areas in the Arctic contain dry tundra, which is likely to make a different contribution to the C fluxes than wet tundra. In this study we examined the seasonal variations in ecosystem CO ₂ emission in a dry subarctic heath in northern Scandinavia. Soil moisture level during most of the season was below 250% dry weight of the soil, which is a moisture level below which previous research has shown that microbial activity becomes increasingly moisture limited. Along with measurements throughout the season of CO ₂ emission from plants and soil, soil temperatures, and moisture levels, we added N, P, sugar, and cornstarch. Except for a strong response to sugar addition, the short-term effect of soil temperature and moisture on seasonal CO ₂ emission was much stronger than the responses to the additions. A regression model showed that respiration rates also in this relatively dry tundra are strongly controlled primarily by soil moisture conditions. However, the CO ₂ efflux is likely to increase with increased moisture levels and decrease with drying, which is contrary to expected responses in wet tundra.