Effects of dry and wet N deposition on vegetation and biogeochemistry of an ombrotrophic bog

It has repeatedly been shown that increased nitrogen (N) deposition results in dramatic shifts in vegetation composition. The sources of N-deposition vary from agriculture (mainly NH3 and NH4) to industry and traffic (mainly NOx). Effects of these different N forms on the vegetation and biogeochemistry of an ombrotrophic peat bog, Whim Moss (~15km southwest of Edinburgh), have been investigated since April 2002, by employing an automate N manipulation system. This field experiment, uniquely, offers the possibility to investigate the effects of the different N forms at the same site and at application rates and deposition scenarios simulating natural variation in rainfall. Within the manipulation system there are two N manipulations: Dry, where gaseous NH3 is released over a 60 m transect at concentrations that simulate a 100,000 bird poultry unit (0.4-200 μg m-3), and Wet, as soluble nitrate or ammonium, covering the full range of UK wet N-deposition (8 – 64 kg N ha-1yr-1). The effects of dry N deposition on the vegetation and biogeochemistry at different distances from the NH3 source have been analysed. In the wet N deposition experiment, 5 treatments were followed, ranging from 8-64 kg N ha-1yr-1 and differing in N form as either oxidised or reduced N. Samples of soil water were obtained using mini-rhizon samplers and were tested for pH, NH4, NO3, P and base cations. Young (1 year old) shoots of Calluna vulgaris L. (Hull), Erica tetralix L. and Sphagnum capillifolium Ehrh. (Hedw.) were harvested and tested for chlorophyll concentrations, aminoacids and P and base cation concentrations in acid digests. The preliminary results show differences between treatment N forms and N doses and along the NH3 gradient. In this presentation we will focus on the plant responses to the changes in the biochemistry. CAPER Conference