Climatic factors alone would seem to sufficiently explain limited plant growth on the arctic tundra, but experiments using inorganic fertilizers have demonstrated that arctic vegetation is well-adapted to the cold itself. Instead, the limiting factor on primary production in the Arctic is lack of nutrients due to slow decomposition of previous years’ growth. Tundra plants are therefore battling for essential elements—primarily nitrogen (N). The tussock-forming sedge Eriophorum vaginatum thrives under these conditions. The ability to use organic N seems key. Rates of N mineralization in Alaskan arctic soils are insufficient to provide the N needed for observed net primary production, suggesting that tundra plants make use of other sources of N. It has since been demonstrated that E. vaginatum not only takes up, but prefers the amino acid glycine as a source of N as compared to the mineralized N forms ammonium (NH4+) or nitrate (NO3-) in laboratory settings. We therefore hypothesize that amino acids provide a significant proportion of E. vaginatum’s annual N uptake. Using microdialysis, a minimally invasive membrane-based technique of collecting dissolved molecules, we measured amino acid concentration, supply, and uptake for E. vaginatum tussocks.
Results/Conclusions
We found that tundra soil provides small quantities of glutamate, glycine, serine, lysine, and alanine over a single hour. The total amino acid supply was greater than or equal to the supply of ammonium, and nitrate was undetectable. E. vaginatum can take up glycine and alanine; other amino acids remain to be tested. Our results confirm that the N budget for Alaskan tussock tundra is incomplete if small organics are not included in the plant-available pool.