Changing sub-Arctic tundra vegetation upon permafrost degradation: impact on foliar mineral element cycling

Abstract

Abstract. Arctic warming and permafrost degradation are modifying northern ecosystems through changes in microtopography, soil water dynamics, nutrient availability, and vegetation succession. Upon permafrost degradation, the release of deep stores of nutrients such as nitrogen and phosphorus from newly thawed permafrost stimulates Arctic vegetation production. More specifically, wetter lowlands show an increase in sedges (as part of graminoids), whereas drier uplands favor shrub expansion. In turn, shifts in the composition of vegetation may influence local mineral element cycling through litter production. In this study, we evaluate the influence of permafrost degradation on mineral element foliar stocks and potential annual fluxes upon litterfall. We measured the foliar elemental composition (Al, Ca, Fe, K, Mn, P, S, Si, and Zn) on ~500 samples of typical tundra vegetation species from two contrasting Alaskan sites, i.e., under experimental (CiPEHR) and ambient (Gradient) warming. The foliar concentration of these mineral elements was species specific, with sedge leaves having relatively high Si concentration, and shrub leaves having relatively high Ca and Mn concentrations. Therefore, changes in the species biomass composition of the Arctic tundra in response to permafrost thaw are expected to be the main factors that dictate changes in elemental composition of foliar stocks and maximum potential foliar fluxes upon litterfall. We observed an increase in the mineral element foliar stocks and potential annual litterfall fluxes, with Si increasing with sedge expansion in wetter sites (CiPEHR), and Ca and Mn increasing with shrub expansion in drier sites (Gradient). Consequently, we expect that sedge and shrub expansion upon permafrost thaw will lead to changes in litter elemental composition, and affect nutrient cycling across the sub-Arctic tundra, with potential implications for further vegetation succession.

Plant foliar nutrient response to active layer and water table depth in warming permafrost soils

“…Betula nana was found to increase near-surface long-lived fine root biomass in a fertilization experiment (Sullivan et al, 2007), which could partially explain its successful eventual replacement of E. vaginatum (which has an annual root system) in long-term Arctic fertilization experiments (Shaver and Chapin, 1995;Shaver et al, 2001). Recent studies have suggested that initial uptake of nutrients by fast-growing graminoids and other deeply rooted forbs may move nutrients above-ground in the form of more quickly decomposing litter, where shrubs may then access it over longer time-scales (Wookey et al, 2009;Hewitt et al, 2019;Mauclet, Agnan, et al, 2021).…”

Quantifying stocks in exchangeable base cations in permafrost: a reserve of nutrients about to thaw

“…Non-vascular plant cover is dominated by mosses (mainly Sphagnum spp., Dicranum spp., and feather mosses including Hylocomium splendens and Pleurozium schreberi) and lichen species (e.g., Nephroma spp., Cladonia spp., and Flavocetraria cucullata) (Deane-Coe et al, 2015;Natali et al, 2012;Schuur et al, 2007). Since the start of the thermokarst development, vegetation cover changed with the evergreen and deciduous shrubs (as V. uliginosum and R. tomentosum), and forbs (as R. chamaemorus) being dominant at the expense of the sedges (Jasinski et al, 2018;Mauclet et al, 2021;Schuur et al, 2007;Villani et al, 2022).…”