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. These 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) of ∼ 500 samples of typical tundra plant species from two contrasting Alaskan tundra sites, i.e., an experimental 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 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 therefore 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).…”

A snap-shot assessment of carbon emission and export in a pristine river draining permafrost peatlands (Taz River, Western Siberia)

“…Such an approach has been successfully used in western Siberia (Frey and Smith, 2005) to model the possible future changes in small (Krickov et al, 2018) and medium-size rivers, lakes (Manasypov et al, 2022), soil waters (Raudina et al, 2018) and permafrost ice (Lim et al, 2021). Indeed, with permafrost boundary shift northward (Romanovsky et al, 2010) and tundra greening over next decades as it is observed generally through the Arctic and subarctic regions (Tape et al, 2006;Garcia Criado et al, 2020;Mauclet et al, 2022), the northern part of the Taz River (tundra and forest-tundra of continuous to discontinuous permafrost) can be entirely transformed into southern part-like territory of taiga and forest-tundra biome with discontinuous to sporadic permafrost. Given that the CO 2 flux in the upper (southern) 400 km of the river main stem and tributaries is a factor of 2-3 higher than that in the lower (northern) part of the basin, one can expect a 2 to 3-fold increase in the CO 2 emission from the Taz River basin due to on-going climate warming and permafrost thaw.…”

Hydrochemistry of Medium-Size Pristine Rivers in Boreal and Subarctic Zone: Disentangling Effect of Landscape Parameters across a Permafrost, Climate, and Vegetation Gradient

“…Such an approach has been successfully used in western Siberia since the pioneering work of Frey and Smith [12] to model possible future changes in small rivers [13,59], lakes [61], soil waters [23], and permafrost ice [21]. Indeed, with permafrost and forest boundary shift northward over next decades [9,[63][64][65], the northern part of the Taz River (tundra and forest-tundra of continuous to discontinuous permafrost) can be entirely transformed into southern part-like territory of taiga and forest-tundra biome with discontinuous to sporadic permafrost, whereas the entire Ket River basin can be used as a surrogate for hydrochemistry for the southern part of the Taz River. The mean element concentrations in the main stem and tributaries in the two subbasins of the Taz and Ket River are illustrated in Figure 8.…”