Effects of increased deposition of atmospheric nitrogen on an upland Calluna moor: N and P transformations

Pilkington, Michael G., Caporn, Simon J.M., Carroll, Jacqueline A., Cresswell, Neil, Lee, John A., Emmett, Bridget A. and Johnson, David (2005) Effects of increased deposition of atmospheric nitrogen on an upland Calluna moor: N and P transformations. Environmental Pollution, 135 (3). pp. 469-480. ISSN 0269-7491

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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 N2O 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 N2O 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. ©2005 Elsevier Ltd. All rights reserved.