Articles | Volume 13, issue 15
Research article
01 Aug 2016
Research article |  | 01 Aug 2016

Decadal and long-term boreal soil carbon and nitrogen sequestration rates across a variety of ecosystems

Kristen L. Manies, Jennifer W. Harden, Christopher C. Fuller, and Merritt R. Turetsky

Abstract. Boreal soils play a critical role in the global carbon (C) cycle; therefore, it is important to understand the mechanisms that control soil C accumulation and loss for this region. Examining C & nitrogen (N) accumulation rates over decades to centuries may provide additional understanding of the dominant mechanisms for their storage, which can be masked by seasonal and interannual variability when investigated over the short term. We examined longer-term accumulation rates, using 210Pb and 14C to date soil layers, for a wide variety of boreal ecosystems: a black spruce forest, a shrub ecosystem, a tussock grass ecosystem, a sedge-dominated ecosystem, and a rich fen. All ecosystems had similar decadal C accumulation rates, averaging 84 ± 42 gC m−2 yr−1. Long-term (century) C accumulation rates were slower than decadal rates, averaging 14 ± 5 gC m−2 yr−1 for all ecosystems except the rich fen, for which the long-term C accumulation rates was more similar to decadal rates (44 ± 5 and 76 ± 9 gC m−2 yr−1, respectively). The rich fen also had the highest long-term N accumulation rates (2.7 gN m−2 yr−1). The lowest N accumulation rate, on both a decadal and long-term basis, was found in the black spruce forest (0.2 and 1.4 gN m−2 yr−1, respectively). Our results suggest that the controls on long-term C and N cycling at the rich fen is fundamentally different from the other ecosystems, likely due to differences in the predominant drivers of nutrient cycling (oxygen availability, for C) and reduced amounts of disturbance by fire (for C and N). This result implies that most shifts in ecosystem vegetation across the boreal region, driven by either climate or succession, will not significantly impact regional C or N dynamics over years to decades. However, ecosystem transitions to or from a rich fen will promote significant shifts in soil C and N storage.

Short summary
Boreal soils are important to the global C cycle. We need to understand what controls how C accumulates and is lost from this soil. To help we examined C & N accumulation rates for five boreal ecosystems. Most ecosystems were similar. But the rich fen had higher long-term C & N accumulation rates, likely due to differences in nutrient cycling & because it burns less. Therefore, shifts among ecosystems will not change regional C & N dynamics much, unless there is a shift to or from a rich fen.
Final-revised paper