Soil Greenhouse Gas Fluxes, Environmental Controls, and the Partitioning of N₂O Sources in UK Natural and Seminatural Land Use Types

Abstract

Natural and seminatural terrestrial ecosystems (unmanaged peatlands and forests and extensive and intensive grasslands) have been under‐represented in the UK greenhouse gas (GHG) inventory. Mechanistic studies of GHG fluxes and their controls can improve the prediction of the currently uncertain GHG annual emission estimates. The source apportionment of N2O emissions can further inform management plans for GHG mitigation. We have measured in situ GHG fluxes monthly in two replicated UK catchments and evaluated their environmental controlling factors. An adapted 15N‐gas flux method with low addition of 15N tracer (0.03–0.5 kg 15N ha−1) was used to quantify the relative contribution of denitrification to net N2O production. Total N2O fluxes were 40 times higher in the intensive grasslands than in the peatlands (range: −1.32 to 312.3 μg N m−2 h−1). The contribution of denitrification to net N2O emission varied across the land use types and ranged from 9 to 60%. Soil moisture was the key parameter regulating the partitioning of N2O sources (r2 = 0.46). Total N2O fluxes were explained by a simple model (r2 = 0.83) including parameters such as total dissolved nitrogen, organic carbon, and water content. A parsimonious model with the soil moisture content as a single scalar parameter explained 84% of methane flux variability across land uses. The assumption that 1% of the atmospherically deposited N on natural ecosystems is emitted as N2O could be overestimated or underestimated (0.3–1.6%). The use of land use‐specific N2O emission factors and further information on N2O source partitioning should help constrain this uncertainty.

Nitrogen-rich organic soils under warm well-drained conditions are global nitrous oxide emission hotspots

“…This may have been partially due to the short time span of our measurements per site. However, that is consistent with the meta-analysis of published data in eleven papers showing no correlation between long-term N 2 O fluxes and soil temperature 17 , 24 , 31 , 32 , 34 , 53 – 58 . The test for an upper boundary 59 in our temperature data was negative ( p > 0.05).…”

“…We only included publications that reported time series of at least a year’s duration that reported N 2 O fluxes and simultaneous soil temperature and soil moisture observations (either VWC or WFPS). Eleven papers 17 , 24 , 31 , 32 , 34 , 53 – 58 qualified under these criteria. The study sites were fairly evenly distributed throughout major organic soil regions of the world.…”

“…The study sites were fairly evenly distributed throughout major organic soil regions of the world. Only three of these papers reported soil NO 3 − concentrations 17 , 24 , 58 . We converted the WFPS values to VWC as follows 66 : …”

New Breeding Techniques for Greenhouse Gas (GHG) Mitigation: Plants May Express Nitrous Oxide Reductase

“…Assuming the tobacco yield to be 0.50 tonne/ha [116], the calculated N2O-cracking ability of the nosZ-expressing tobacco could be as high as 600 kg of N2O/ha/day [115], or 60 tonnes/ha/year (100 day growing season). This value surpasses the calculated N2O flux of 0.05-1.98 kg N2O/ha/year [117]. In other words, if every tobacco plant in the world produced N2OR, this industrial crop (6.6 million tonnes were produced worldwide in 2016 [118]) could conceivably crack 785 Tg of N2O (1 Tg = 1 million metric tonnes) during an average growing season of 100 days, far surpassing the estimated ~30 Tg of N2O emitted per year [119].…”

Variations in Greenhouse Gas Fluxes in Response to Short-Term Changes in Weather Variables at Three Elevation Ranges, Wakiso District, Uganda

“…One of the leading mechanisms behind the increased soil CH 4 flux in the soil is decreasing O 2 diffusion [71]. The flooding episodes could have led to poorly drained soils, resulting in CH 4 production [72]. As reported by Chamberlain et al [73], soil CH 4 flux from a flooded ecosystem can be a product of CH 4 production, consumption, and transport within soils and water.…”