Abstract
Deciduous shrubs are expanding across the graminoid-dominated nutrient-poor arctic tundra. Absorptive root traits of shrubs are key determinants of nutrient acquisition strategy from tundra soils, but the variations of shrub root traits within and among common shrub genera across the arctic climatic gradient are not well resolved. Consequently, the impacts of arctic shrub expansion on belowground nutrient cycling remain largely unclear. Here, we collected roots from 170 plots of three commonly distributed shrub genera (Alnus, Betula, and Salix) and a widespread sedge (Eriophorum vaginatum) along a climatic gradient in northern Alaska. Absorptive root traits that are relevant to the strategy of plant nutrient acquisition were determined. The influence of aboveground dominant vegetation cover on the standing root biomass, root productivity, vertical rooting profile, as well as the soil nitrogen (N) pool in the active soil layer was examined. We found consistent root trait variation among arctic plant genera along the sampling transect. Alnus and Betula had relatively thicker and less branched, but more frequently ectomycorrhizal colonized absorptive roots than Salix, suggesting complementarity between root efficiency and ectomycorrhizal dependence among the co-existing shrubs. Shrub-dominated plots tended to have more productive absorptive roots than sedge-dominated plots. At the northern sites, deep absorptive roots (>20 cm depth) were more frequent in birch-dominated plots. We also found shrub roots extensively proliferated into the adjacent sedge-dominated plots. The soil N pool in the active layer generally decreased from south to north but did not vary among plots dominated by different shrub or sedge genera. Our results reveal diverse nutrient acquisition strategies and belowground impacts among different arctic shrubs, suggesting that further identifying the specific shrub genera in the tundra landscape will ultimately provide better predictions of belowground dynamics across the changing arctic.
Highlights
Plant roots are essential for nutrient acquisition across global biomes
Variations of root traits can exist among the common arctic plants, but whether the complementary variation in root vs. mycorrhizal fungal dependence of nutrient acquisition exists among arctic plants remains to be tested (Iversen et al, 2015)
The normalized difference vegetation index (NDVI) data obtained by the Advanced Very High-Resolution Radiometer (AVHRR) was retrieved from Google Earth Engine’s public catalog using the platform’s JavaScript API
Summary
Plant roots are essential for nutrient acquisition across global biomes. The diversity of root characteristics (“root traits,” e.g., root thickness) among different plant species indicates varying nutrient acquisition strategies (Fitter, 1982; Bardgett et al, 2014; Ma et al, 2018). Studies in tropical and temperate biomes suggest that plant species that mainly rely on the root pathway in nutrient acquisition tend to form thinner roots with higher nitrogen (N) concentrations, which enable them to more rapidly leverage resources for soil exploration. Variations of root traits can exist among the common arctic plants, but whether the complementary variation in root vs mycorrhizal fungal dependence of nutrient acquisition exists among arctic plants remains to be tested (Iversen et al, 2015)
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