Long-term nitrogen deposition increases heathland carbon sequestration

Chris D Field; Chris D Evans; Nancy B Dise; Jane R Hall; Simon J M Caporn

doi:10.1016/j.scitotenv.2017.03.059

Long-term nitrogen deposition increases heathland carbon sequestration

Sci Total Environ. 2017 Aug 15:592:426-435. doi: 10.1016/j.scitotenv.2017.03.059. Epub 2017 Mar 21.

Authors

Chris D Field¹, Chris D Evans², Nancy B Dise³, Jane R Hall², Simon J M Caporn⁴

Affiliations

¹ School of Science and Environment, Manchester Metropolitan University, John Dalton Building, Chester Street, Manchester, M1 5GD, UK. Electronic address: c.field@mmu.ac.uk.
² Centre for Ecology and Hydrology Bangor, Environment Centre Wales, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK.
³ Centre for Ecology and Hydrology, Edinburgh EH26 0QB, UK.
⁴ School of Science and Environment, Manchester Metropolitan University, John Dalton Building, Chester Street, Manchester, M1 5GD, UK.

PMID: 28340453
DOI: 10.1016/j.scitotenv.2017.03.059

Abstract

The large increases in reactive nitrogen (N) deposition in developed countries since the Industrial Revolution have had a marked impact on ecosystem functioning, including declining species richness, shifts in species composition, and increased N leaching. A potential mitigation of these harmful effects is the action of N as a fertiliser, which, through increasing primary productivity (and subsequently, organic matter production), has the potential to increase ecosystem carbon (C) storage. Here we report the response of an upland heath to 10years of experimental N addition. We find large increases in plant and soil C and N pools, with N-driven C sequestration rates in the range of 13-138kgCkg^-¹. These rates are higher than those previously found in forest and lowland heath, mainly due to higher C sequestration in the litter layer. C sequestration is highest at lower N treatments (10, 20, and 40kgNha^-1yr^-1 above ambient), with evidence of saturation at the highest N treatment, reflecting a physiologically aged Calluna vulgaris (Calluna) canopy. To maintain these rates of sequestration, the Calluna canopy should be managed to maximise it's time in the building phase. Scaling our results across UK heathlands, this equates to an additional 0.77Mt CO2e per annum extra C sequestered into plant litter and the top 15cm of heathland soil as a result of N deposition. The bulk of this is found in the litter and organic soil horizons that hold an average of 23% and 54% of soil C, respectively. This additional C represents around 0.44% of UK annual anthropogenic GHG emissions. When considered in the context of falling biodiversity and altered species composition in heathland, policy focus should remain on reducing N emissions.

Keywords: Carbon sequestration; Heathlands; Nitrogen deposition; Pools; Storage.