In situ nitrogen uptake from inorganic and organic sources by the fine root systems of five alpine woody plant species

Abstract Alpine forests are characterized by cold conditions and poor nutrient availability. Knowledge of nitrogen (N) uptake by fine roots is necessary to understand the survival strategies of plants in these severe environments. We aimed to characterize species-specific inorganic and organic N uptake rates and their root traits in five dominant alpine woody plant species: the ectomycorrhizal (ECM) species Pinus pumila and Alnus maximowiczii , and the ericoid mycorrhizal (ERM) species Empetrum nigrum var. japonicum, Rhododendron aureum , and Vaccinium vitis-idaea . The inorganic and organic N uptake rates from the fine-root systems were measured directly using the solution-depletion method. Root traits, such as diameter, specific root length, root tissue density, and root N concentration, were also determined through morphological and chemical analyses of the incubated roots. Total N uptake rates were higher in ERM species, particularly in Vaccinium vitis-idaea . The proportion of inorganic N uptake was greater in ECM species than in ERM species, while the proportion of organic N uptake was generally higher in ERM species. Root diameter was the best predictor of N uptake rates, and specific root length and root tissue density were linked to preferences for inorganic and organic N, respectively. Thus, alpine woody plants altered N uptake and preference by modifying root traits, potentially promoting N niche acquisition in competition among species or mycorrhizal types, and enhancing plant survival in the alpine zone.