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Abstract. Arctic warming and permafrost degradation are modifying northernecosystems through changes in microtopography, soil water dynamics, nutrientavailability, and vegetation succession. Upon permafrost degradation, therelease of deep stores of nutrients, such as nitrogen and phosphorus, fromnewly thawed permafrost stimulates Arctic vegetation production. Morespecifically, wetter lowlands show an increase in sedges (as part ofgraminoids), whereas drier uplands favor shrub expansion. These shifts inthe composition of vegetation may influence local mineral element cyclingthrough litter production. In this study, we evaluate the influence ofpermafrost degradation on mineral element foliar stocks and potential annualfluxes upon litterfall. We measured the foliar elemental composition (Al,Ca, Fe, K, Mn, P, S, Si, and Zn) of ∼ 500 samples of typicaltundra plant species from two contrasting Alaskan tundra sites, i.e., anexperimental sedge-dominated site (Carbon in Permafrost Experimental Heating Research, CiPEHR) and natural shrub-dominated site(Gradient). The foliar concentration of these mineral elements was species specific, with sedge leaves having relatively high Si concentration andshrub leaves having relatively high Ca and Mn concentrations. Therefore,changes in the species biomass composition of the Arctic tundra in responseto permafrost thaw are expected to be the main factors that dictate changesin elemental composition of foliar stocks and maximum potential foliarfluxes upon litterfall. We observed an increase in the mineral elementfoliar stocks and potential annual litterfall fluxes, with Si increasingwith sedge expansion in wetter sites (CiPEHR), and Ca and Mn increasing withshrub expansion in drier sites (Gradient). Consequently, we expect thatsedge and shrub expansion upon permafrost thaw will lead to changes inlitter elemental composition and therefore affect nutrient cycling acrossthe sub-Arctic tundra with potential implications for further vegetationsuccession.
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Permafrost Thaw Accelerates Old Soil Carbon Release, Outpacing New Plant Inputs During a 13‐Year Tundra Warming Experiment
ABSTRACT Massive stores of ancient soil organic carbon (SOC) in permafrost can decompose with Arctic warming and accelerate global climate change. Declining SOC stocks are central to the permafrost carbon feedback, but direct measures of SOC loss are extremely rare due to methodological challenges related to subsidence in the Arctic. To fully capture changing SOC dynamics during thaw, we directly measured SOC stock and bulk soil radiocarbon (14C) changes, while accounting for subsidence, during 13 years of permafrost thaw in a warming experiment in Interior Alaska. We found significant declines in SOC stocks: 14% (± 6%) in ambient plots that experienced regional warming and 23% (± 5%) in snow fence warmed plots, entirely in deep, mineral soil layers. Losses were largely driven by winter soil warming but were mediated by changing soil moisture and vegetation conditions. Plots with low shrub biomass had greater SOC losses, suggesting that vegetation community composition may play an important role in SOC storage. Surface soil14C measurements suggest that carbon inputs were three times greater in warming plots compared to ambient plots, but that decomposition increased proportionally leading to no detectable change in surface organic layers. We observed significant SOC losses of 5.2–8.1 kg C m−2from deeper soil layers where carbon was sequestered ~2400 to ~4500 years ago. Our findings indicate that warmer soils in the winter will accelerate SOC losses, but that increasing density of shrub species through shrub expansion could help to mitigate SOC losses in deep soils. The significant loss of SOC from deep, mineral soils observed over just 13 years of ambient and experimental permafrost thaw highlights the vulnerability of this old C pool as it enters the active global carbon cycle.
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- Award ID(s):
- 2224776
- PAR ID:
- 10665543
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 31
- Issue:
- 12
- ISSN:
- 1354-1013
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/gcb.70609
