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

摘要

It has repeatedly been shown that increased nitrogen (N) deposition results in dramaticudshifts in vegetation composition. The sources of N-deposition vary from agricultureud(mainly NH3 and NH4) to industry and traffic (mainly NOx).udEffects of these different N forms on the vegetation and biogeochemistry of anudombrotrophic peat bog, Whim Moss (~15km southwest of Edinburgh), have beenudinvestigated since April 2002, by employing an automate N manipulation system. Thisudfield experiment, uniquely, offers the possibility to investigate the effects of the different Nudforms at the same site and at application rates and deposition scenarios simulatingudnatural variation in rainfall. Within the manipulation system there are two N manipulations:udDry, where gaseous NH3 is released over a 60 m transect at concentrations that simulateuda 100,000 bird poultry unit (0.4-200 μg m-3), and Wet, as soluble nitrate or ammonium,udcovering the full range of UK wet N-deposition (8 – 64 kg N ha-1yr-1).udThe effects of dry N deposition on the vegetation and biogeochemistry at differentuddistances from the NH3 source have been analysed. In the wet N deposition experiment, 5udtreatments were followed, ranging from 8-64 kg N ha-1yr-1 and differing in N form as eitherudoxidised or reduced N.udSamples of soil water were obtained using mini-rhizon samplers and were tested for pH,udNH4, NO3, P and base cations. Young (1 year old) shoots of Calluna vulgaris L. (Hull),udErica tetralix L. and Sphagnum capillifolium Ehrh. (Hedw.) were harvested and tested forudchlorophyll concentrations, aminoacids and P and base cation concentrations in aciduddigests.udThe preliminary results show differences between treatment N forms and N doses andudalong the NH3 gradient. In this presentation we will focus on the plant responses to theudchanges in the biochemistry.udCAPER Conference