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

Abstract

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 À1 yr À1, 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.

Mercury evasion from a boreal peatland shortens the timeline for recovery from legacy pollution

“…The vertical distribution of Hg in surface peat might however also result from decay of organic matter and cannot be interpreted only as a result of changes in Hg deposition and GEM evasion 57 . The surface peat decay rate constant at Degerö Stormyr is 0.0158 yr −1 58 resulting in a vertical THg profile similar to the ones observed. However, our results indicate that besides changes in peat mass production and decay processes, GEM evasion has the potential to alter the signal in the vertical peat profile from atmospheric Hg deposition.…”

Nitrogen limitation of heterotrophic biofilms in boreal streams

“…Our study is the first to demonstrate N limits microbial biofilms in boreal streams and fills an important knowledge gap regarding nutrient limitation in the boreal landscape. Furthermore, our results add to a growing body of evidence that the productivity of northern boreal landscapes, not subject to high rates of atmospheric N deposition, is principally constrained by N, as indicated by similar patterns following experimental N enrichment of trees (Högberg et al ., ), soils (Hasselquist, Metcalfe & Högberg, ), lake phytoplankton (Jansson et al ., ; Bergström et al ., ) and mire vegetation (Olid et al ., ). The degree to which N serves as the principal constraint to biofilm metabolism throughout the year is, however, still unknown.…”

Long-term macronutrient stoichiometry of UK ombrotrophic peatlands

“…A key characteristic of ombrotrophic bogs is that N, P and other elements (e.g., Ca, K, Mg) vital to their biogeochemical functioning (Bridgham et al, 1998;Bubier et al, 2007;Damman, 1986) and plant assemblage structure (Baker and Boatman, 1990;Fritz et al, 2012;Gotelli et al, 2008) are almost exclusively supplied via the atmosphere (Damman, 1990;Kellogg and Bridgham, 2003;Malmer, 1988). Such inputs of N and P are estimated to be low (Tipping et al, 2014;Turunen et al, 2004), suggesting that their availability should limit peat bog primary production (Schlesinger and Bernhardt, 2013), an effect that has been demonstrated experimentally (Aerts et al, 1992;Aerts et al, 2001;Olid et al, 2014). Although they are both supplied from the atmosphere, N and P differ in the mechanisms by which this supply takes place.…”