Ecosystem responses to differing ratios of reduced and oxidised nitrogen inputs

Stevens, Carly and Manning, P. and van den Berg, L. and Lamers, L. and de Graaf, M.C.C. and Wamelink, W. and Boxman, A. and Bleeker, A. and Vergeer, P. and Arroniz-Crespo, M. and Limpens, J. and Bobbink, R. and Dorland, E. (2011) Ecosystem responses to differing ratios of reduced and oxidised nitrogen inputs. Environmental Pollution, 159 (3). pp. 665-676. ISSN 0269-7491

Abstract

While it is well established that ecosystems display strong responses to elevated nitrogen deposition, the importance of the ratio between the dominant forms of deposited nitrogen (NHx and NOy) in determining ecosystem response is poorly understood. As large changes in the ratio of oxidised and reduced nitrogen inputs are occurring, this oversight requires attention. One reason for this knowledge gap is that plants experience a different NHx:NOy ratio in soil to that seen in atmospheric deposits because atmospheric inputs are modified by soil transformations, mediated by soil pH. Consequently species of neutral and alkaline habitats are less likely to encounter high NH4+ concentrations than species from acid soils. We suggest that the response of vascular plant species to changing ratios of NHx:NOy deposits will be driven primarily by a combination of soil pH and nitrification rates. Testing this hypothesis requires a combination of experimental and survey work in a range of systems.