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Abstract Retrogressive thaw slumps (RTS)—thermal erosion of soil and vegetation after ground ice thaw—are increasing. Recovery of plant biomass after RTS is important for maintaining Arctic carbon (C) stocks and is regulated by nutrient availability for new plant growth. Many RTS are characterized by verdant shrub growth mid-succession, atypical of the surrounding nutrient-limited tundra. Here, we investigated the potential for internal and external sources of nitrogen (N) and phosphorus (P) to support mid-successional shrub growth at three Alaskan RTS chronosequences. We assessed patterns of soil and microbial CNP, soil NP cycling rates and stocks, N inputs via biological N2-fixation, and thaw leachate over time after disturbance. We found a clear transfer of P stocks from mineral to organic soils with increasing site age, yet insufficient N from any one source to support observed shrub growth. Instead, multiple mechanisms may have contributed to mid-successional shrub growth, including sustained N-cycling with reduced plant biomass, N leaching from undisturbed tundra, uninvestigated sources of N2-fixation, and most promising given the large resource, deep mineral soil N stocks. These potential mechanisms of N supply are critical for the regulation of the Arctic C cycle in response to an increasingly common climate-driven disturbance.
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Changing sub-Arctic tundra vegetation upon permafrost degradation: impact on foliar mineral element cycling
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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- Award ID(s):
- 1636476
- PAR ID:
- 10399367
- Date Published:
- Journal Name:
- Biogeosciences
- Volume:
- 19
- Issue:
- 9
- ISSN:
- 1726-4189
- Page Range / eLocation ID:
- 2333 to 2351
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/bg-19-2333-2022
