Abstract
Soil emissions of NO and N2O from typical land uses across Lowland and Highland Scotland were simulated under climate change conditions, during a short-term laboratory study. All locations investigated were significant sources of N2O (range: 157–277 µg N2O–N m−2 h−1) and low-to-moderate sources of NO emissions (range: 0.4–30.5 µg NO–N m−2 h−1), with a general tendency to decrease with altitude and increase with fertiliser and atmospheric N inputs. Simulated climate warming and extreme events (drought, intensive rainfall) increased soil NO pulses and N2O emissions from both natural and managed ecosystems in the following order: natural Highlands < natural Lowlands < grazed grasslands < natural moorland receiving high NH3 deposition rates. Largest NO emission rates were observed from natural moorlands exposed to high NH3 deposition rates. Although soil NO emissions were much smaller (6–660 times) than those of N2O, their impact on air quality is likely to increase as combustion sources of NO x are declining as a result of successful mitigation. This study provides evidence of high N emission rates from natural ecosystems and calls for urgent action to improve existing national and intergovernmental inventories for NO and N2O, which at present do not fully account for emissions from natural soils receiving no direct anthropogenic N inputs.
Highlights
Managed soils, including grazed grasslands (GGs), receiving high nitrogen (N) input are known to be significant sources of the atmospheric pollutant ammonia (NH3); nitrous oxide (N2O), a powerful greenhouse gas (GHG) in the troposphere and a strong stratospheric ozone depletion agent; and nitric oxide (NO), an atmospheric pollutant and a precursor of tropospheric ozone [1, 2]
It is well documented that N deposition may increase carbon sequestration in forest ecosystems until N saturation status is reached [6]; thereafter forests may turn into a significant source of NO and to a lesser extend N2O emissions [7,8,9]
Drivers controlling soil NO and N2O emissions under drought with increased temperature in different land uses In this short incubation study, we have shown that typical land use categories in the Lowland and Highland regions responded differently to soil NO emissions, compared to N2O emissions when subjected to simulated drought conditions and changes in temperature (figures 1(b) and (c))
Summary
Managed soils, including grazed grasslands (GGs), receiving high nitrogen (N) input are known to be significant sources of the atmospheric pollutant ammonia (NH3); nitrous oxide (N2O), a powerful greenhouse gas (GHG) in the troposphere and a strong stratospheric ozone depletion agent; and nitric oxide (NO), an atmospheric pollutant and a precursor of tropospheric ozone [1, 2]. Natural and semi-natural ecosystems located in the vicinity of agricultural activities may be exposed to increased deposition rates of N gases and aerosols [3,4,5]. It is well documented that N deposition may increase carbon sequestration in forest ecosystems until N saturation status is reached [6]; thereafter forests may turn into a significant source of NO and to a lesser extend N2O emissions [7,8,9]. Excessive N deposition to a typical peatland ecosystem (Whim Bog, South East Scotland) altered bryophyte growth, species dominance, and enhanced Sphagnum decomposition rates [11], while dry deposition of NH3 led to increased soil water nitrates and N2O emissions [12, 13]
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