title: Nitrogen accumulation and partitioning in a High Arctic tundra ecosystem from extreme atmospheric N deposition events.
abstract: Arctic ecosystems are threatened by pollution from recently detected extreme atmospheric nitrogen (N) deposition events in which up to 90% of the annual N deposition can occur in just a few days. We undertook the first assessment of the fate of N from extreme deposition in High Arctic tundra and are presenting the results from the whole ecosystem (15)N labelling experiment. In 2010, we simulated N depositions at rates of 0, 0.04, 0.4 and 1.2 g Nm(-2)yr(-1), applied as (15)NH4(15)NO3 in Svalbard (79(°)N), during the summer. Separate applications of (15)NO3(-) and (15)NH4(+) were also made to determine the importance of N form in their retention. More than 95% of the total (15)N applied was recovered after one growing season (~90% after two), demonstrating a considerable capacity of Arctic tundra to retain N from these deposition events. Important sinks for the deposited N, regardless of its application rate or form, were non-vascular plants>vascular plants>organic soil>litter>mineral soil, suggesting that non-vascular plants could be the primary component of this ecosystem to undergo measurable changes due to N enrichment from extreme deposition events. Substantial retention of N by soil microbial biomass (70% and 39% of (15)N in organic and mineral horizon, respectively) during the initial partitioning demonstrated their capacity to act as effective buffers for N leaching. Between the two N forms, vascular plants (Salix polaris) in particular showed difference in their N recovery, incorporating four times greater (15)NO3(-) than (15)NH4(+), suggesting deposition rich in nitrate will impact them more. Overall, these findings show that despite the deposition rates being extreme in statistical terms, biologically they do not exceed the capacity of tundra to sequester pollutant N during the growing season. Therefore, current and future extreme events may represent a major source of eutrophication.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, UK; Management School, University of Sheffield, Conduit Road, Sheffield S10 1FL, UK. Electronic address: S.Choudhary@sheffield.ac.uk.
authors.forename: Sonal
authors.initials: S
authors.lastname: Choudhary
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, UK.
authors.forename: Aimeric
authors.initials: A
authors.lastname: Blaud
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, UK; School of Applied Sciences, RMIT University, PO Box 71, Bundoora, VIC 3083, Australia.
authors.forename: A Mark
authors.initials: AM
authors.lastname: Osborn
authors.affiliation: School of Biosciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK; Manchester Metropolitan University, Manchester, M15 6BH, UK.
authors.forename: Malcolm C
authors.initials: MC
authors.lastname: Press
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, UK.
authors.forename: Gareth K
authors.initials: GK
authors.lastname: Phoenix
mesh_terms: D001110:Arctic Regions; D001272:Atmosphere / Q000737:chemistry; D018533:Biomass; D004784:Environmental Monitoring; D004785:Environmental Pollutants / Q000032:analysis*; D009584:Nitrogen / Q000032:analysis*; D012987:Soil / Q000737:chemistry; D013538:Svalbard; D065929:Tundra
chemical_list: D004785:Environmental Pollutants; D012987:Soil; D009584:Nitrogen
keywords: (15)N tracer; Arctic tundra N pools; Ecosystem N dynamics; Extreme nitrogen deposition; N immobilisation; Plant–soil interactions