Short- and long-term plant and microbial uptake of 15N-labelled urea in a mesic tundra heath, West Greenland

• Published in: Polar Biology
• Main Authors: Barthelemy, Hélène, Nobel, Liv Alexa, Stark, Sari, Väisänen, Maria, Olofsson, Johan, Michelsen, Anders
• Format: Article in Journal/Newspaper
• Language: English
• Published: Umeå universitet, Institutionen för ekologi, miljö och geovetenskap 2024
• Subjects: 15N labelling; Arctic tundra; Ecosystem N retention; Microbial N immobilization; Plant nitrogen uptake; Urine; Ecology; Ekologi; Arctic; Greenland; Polar Biology; Tundra
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-216900; https://doi.org/10.1007/s00300-023-03209-6

Terrestrial animals are key elements in the cycling of elements in the Arctic where nutrient availability is low. Waste production by herbivores, in particular urine deposition, has a crucial role for nitrogen (N) recycling, still, it remains largely unexplored. Also, experimental evidence is biased toward short-term studies and Arctic regions under high herbivore pressure. In this study, we aimed to examine the fate of N derived from urine in a nutrient poor tundra heath in West Greenland, with historical low level of herbivory. We performed a pulse labelling with 15N-urea over the plant canopy and explored ecosystem N partition and retention in the short-term (2 weeks and 1 year) and longer-term (5 years). We found that all vascular plants, irrespective of their traits, could rapidly take up N-urea, but mosses and lichens were even more efficient. Total 15N enrichment was severely reduced for all plants 5 years after tracer addition, with the exception of cryptogams, indicating that non-vascular plants constituted a long-term sink of 15N-urea. The 15N recovery was also high in the litter suggesting high N immobilization in this layer, potentially delaying the nutrients from urine entering the soil compartment. Long-term 15N recovery in soil microbial biomass was minimal, but as much as 30% of added 15N remained in the non-microbial fraction after 5 years. Our results demonstrate that tundra plants that have evolved under low herbivory pressure are well adapted to quickly take advantage of labile urea, with urine having only a transient effect on soil nutrient availability. Published online: 12 November 2023