Tussock microhabitats increase nitrogen uptake by plants in an alpine wetland

Purpose: Tussock microhabitat is a universal phenomenon in wetlands, where soil and plant properties differ from their surrounding lawns. This study aims to investigate the differences of plant nitrogen (N) uptake between tussocks and lawns, which would further affect ecosystem functions. Methods: A 15N labeling experiment was conducted in tussocks and lawns of an alpine wetland where plant growth is limited by soil available N. 15N label was injected as NH4+, NO3− or glycine in tussocks and lawns at 0–10 or 10–30 cm depths and traced in plants after two hours. Results: The mineral N content was two times higher in the tussocks with better aeration than the lawns. The plant biomass and root-to-shoot ratio were much higher in the tussocks than the lawns. The relative contributions of NH4+, NO3− and glycine to total N uptake were similar between tussocks and lawns at each soil depth, but the plants on the tussocks took up three times more N and had twice the 15N recovery of the lawns. Conclusion: N uptake by plants on the tussocks was 2–4 times higher compared to the lawns likely due to higher plant biomass and root-to-shoot ratio as well as higher mineral N contents in soil. Therefore, despite the area of tussocks being five times smaller than that of lawns, tussocks strongly increase the ecosystem productivity, nutrient utilization and cycling in wetlands. © 2021, The Author(s), under exclusive licence to Springer Nature Switzerland AG.