Influence of Thawing Permafrost on Soil-Plant Mineral Element Transfer: Case Study in Interior Alaska

Abstract:

Current climate warming strongly affects the Arctic region by increasing thaw depths and modifying water table depths in soils. Exposing newly thawed permafrost at depth unlocks mineral nutrients that can boost plant growth, thereby contributing to modify the balance between carbon input and output from permafrost regions. In this changing Arctic environment, how will active layer deepening affect plant mineral nutrient availability, plant mineral nutrient uptake and soil-plant nutrient cycling via litter degradation?

Studies have highlighted that upon thawing, deep-rooted plants benefit from a newly exposed pool of essential nutrients (e.g., N). It is hypothesized that during plant growth, additional mineral elements (e.g., Ca, K, Mg) are also bio-lifted and recycled in surface soil horizons through litter production, providing a potential source of nutrients for shallower rooted plants.
To address this hypothesis and investigate mineral element distribution in plants and soils upon permafrost thaw, we determine the mineral element content (Ca, K, Mg, Na, P, Si, Mn) (i) in plant species from three different plant functional types (sedges, deciduous and evergreen shrubs) and (ii) in the corresponding soil profiles. The plant selection includes species with shallower (e.g., Vaccinium spp.) and deeper (e.g., Carex spp.) rooting depth, across a permafrost thaw gradient at Eight Mile Lake, Central Alaska. In soils, we also determine the availability of Ca, Mg, K, Na for plants from the soil exchange complex.

Plant leaves and soil samples were collected in August – September 2019, corresponding to the maximal thaw depth. The sampling transect (vegetation and related soil profiles) encompasses a wide range of thaw depth (from -48 cm to –96 cm) and water table depth (from 0 cm to –40 cm). Results are discussed considering mineral element distribution in soils, plant rooting depth, and active layer depth to evaluate whether vegetation may access mineral elements from deeper soil horizons, related to the active layer deepening.