The effects of temperature and nitrogen and sulfur additions on carbon accumulation in a nutrient‐poor boreal mire: Decadal effects assessed using 210 Pb peat chronologies

Boreal peatlands are a major long‐term reservoir of atmospheric carbon (C) and play an important role in the global C cycle. It is unclear how C accumulation in peatlands responds to changing temperatures and nutrients (specifically, nitrogen and sulfur). In this study, we assessed how the C input rate and C accumulation rate in decadal old peat layers respond to increased air temperatures (+3.6°C) during the growing season and the annual additions of nitrogen (N) and sulfur (S) (30 and 20 kg ha −1  yr −1 , respectively) over 12 years of field treatments in a boreal mire. An empirical mass balance model was applied to 210 Pb‐dated peat cores to evaluate changes in C inputs, C mass loss, and net C accumulation rates in response to the treatments. We found that (i) none of the treatments generated a significant effect on peat mass loss decay rates, (ii) C input rates were positively affected by N additions and negatively affected by S additions, (iii) the C accumulation rate in the uppermost (10 to 12 cm) peat was increased by N additions and decreased by S additions, and (iv) only air temperature significantly affected the main effects induced by N and S additions. Based on our findings, we argue that C accumulation rates in surface peat layers of nutrient‐poor boreal mires can increase despite the predicted rise in air temperatures as long as N loads increase and acid atmospheric S remains low.