title: Effects of increased deposition of atmospheric nitrogen on an upland Calluna moor: N and P transformations.
abstract: This study determined the effects of increased N deposition on rates of N and P transformations in an upland moor. The litter layer and the surface of the organic Oh horizon were taken from plots that had received long-term additions of ammonium nitrate at rates of 40, 80 and 120 kg N ha(-1) yr(-1). Net mineralisation processes were measured in both field and laboratory incubations. Soil phosphomonoesterase (PME) activity and rates of N(2)O release were measured in laboratory incubations and root-surface PME activity measured in laboratory microcosms using Calluna vulgaris bioassay seedlings. Net mineralisation rates were relatively slow, with net ammonification consistently stimulated by N addition. Net nitrification was marginally stimulated by N addition in the laboratory incubation. N additions also increased soil and root-surface (PME) activity and rates of N(2)O release. Linear correlations were found between litter C:N ratio and all the above processes except net nitrification in field incubations. When compared with data from a survey of European forest sites, values of litter C:N ratio were greater than a threshold below which substantial, N input-related increases in net nitrification rates occurred. The maintenance of high C:N ratios with negligible rates of net nitrification was associated with the common presence of ericaceous litter and a mor humus layer in both this moorland as well as the forest sites.
authors.affiliation: Department of Environmental and Leisure Studies, Manchester Metropolitan University, MMU Cheshire, Crewe Green Road, Crewe, Cheshire CW1 5DU, UK. m.g.pilkington@mmu.ac.uk
authors.forename: M G
authors.initials: MG
authors.lastname: Pilkington
authors.forename: S J M
authors.initials: SJ
authors.lastname: Caporn
authors.forename: J A
authors.initials: JA
authors.lastname: Carroll
authors.forename: N
authors.initials: N
authors.lastname: Cresswell
authors.forename: J A
authors.initials: JA
authors.lastname: Lee
authors.forename: B A
authors.initials: BA
authors.lastname: Emmett
authors.forename: D
authors.initials: D
authors.lastname: Johnson
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D001272:Atmosphere; D029795:Calluna / Q000737:chemistry*; D002980:Climate; D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods; D008903:Minerals; D009584:Nitrogen / Q000032:analysis / Q000737:chemistry*; D009609:Nitrous Oxide / Q000737:chemistry; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry; D010758:Phosphorus / Q000737:chemistry*; D012987:Soil; D012989:Soil Pollutants / Q000032:analysis; D014852:Wales
chemical_list: D000393:Air Pollutants; D008903:Minerals; D012987:Soil; D012989:Soil Pollutants; D010758:Phosphorus; D010744:Phosphoric Monoester Hydrolases; D009609:Nitrous Oxide; D009584:Nitrogen