Abstract
We applied a 15N dilution technique called “Integrated Total Nitrogen Input” (ITNI) to quantify annual atmospheric N input into a peatland surrounded by intensive agricultural practices over a 2-year period. Grass species and grass growth effects on atmospheric N deposition were investigated using Lolium multiflorum and Eriophorum vaginatum and different levels of added N resulting in increased biomass production. Plant biomass production was positively correlated with atmospheric N uptake (up to 102.7 mg N pot−1) when using Lolium multiflorum. In contrast, atmospheric N deposition to Eriophorum vaginatum did not show a clear dependency to produced biomass and ranged from 81.9 to 138.2 mg N pot−1. Both species revealed a relationship between atmospheric N input and total biomass N contents. Airborne N deposition varied from about 24 to 55 kg N ha−1 yr−1. Partitioning of airborne N within the monitor system differed such that most of the deposited N was found in roots of Eriophorum vaginatum while the highest share was allocated in aboveground biomass of Lolium multiflorum. Compared to other approaches determining atmospheric N deposition, ITNI showed highest airborne N input and an up to fivefold exceedance of the ecosystem-specific critical load of 5–10 kg N ha−1 yr−1.
Highlights
One of the main threats to the diversity, functioning, and species composition of most natural and semi-natural aquatic and terrestrial ecosystems is increasing nitrogen (N) input via atmospheric deposition (Rockstro€m et al 2009).Atmospheric N is deposited as sedimenting and nonsedimenting particles and gases in both dry and wet processes on soil and plant surfaces
The determined total airborne N input in both years exceeded the defined ecosystem-specific critical load of 5–10 kg N haÀ1 yrÀ1 at least two- to fivefold
The high share of NH3 on total N input might lead to an increased sensitivity of ombrotrophic vegetation to, for example, frost, growth reduction, and toxic effects such as necrosis when atmospheric N deposition increases
Summary
Atmospheric N is deposited as sedimenting and nonsedimenting particles and gases in both dry and wet processes on soil and plant surfaces (see VDI 4320, Part 1). Gaseous NOx and NH3, as well as NHþ4 and NOÀ3 , are taken up from the atmosphere through stomata and cuticles. Depending on the stomatal compensation point (function of NHþ4 concentration and pH value of plant apoplasts), NH3 can be either taken up or emitted by plants (Mattsson and Schjørring 2003). Both soilborne NHþ4 and NOÀ3 are assimilated into amino acids and are transported to the plant leaves and shoots.
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