title: Forest and grassland cover types reduce net greenhouse gas emissions from agricultural soils.
abstract: Western Canada's prairie region is extensively cultivated for agricultural production, which is a large source of greenhouse gas emissions. Agroforestry systems are common land uses across Canada, which integrate trees into the agricultural landscape and could play a substantial role in sequestering carbon and mitigating increases in atmospheric GHG concentrations. We measured soil CO2, CH4 and N2O fluxes and the global warming potential of microbe-mediated net greenhouse gas emissions (GWPm) in forest and herbland (areas without trees) soils of three agroforestry systems (hedgerow, shelterbelt and silvopasture) over two growing seasons (May through September in 2013 and 2014). We measured greenhouse gas fluxes and environmental conditions at 36 agroforestry sites (12 sites for each system) located along a south-north oriented soil/climate gradient of increasing moisture availability in central Alberta, Canada. The temperature sensitivity of soil CO2 emissions was greater in herbland (4.4) than in forest (3.1), but was not different among agroforestry systems. Over the two seasons, forest soils had 3.4% greater CO2 emission, 36% higher CH4 uptake, and 66% lower N2O emission than adjacent herbland soils. Combining the CO2 equivalents of soil CH4 and N2O fluxes with the CO2 emitted via heterotrophic (microbial) respiration, forest soils had a smaller GWPm than herbland soils (68 and 89kgCO2ha(-1), respectively). While emissions of total CO2 were silvopasture>hedgerow>shelterbelt, soils under silvopasture had 5% lower heterotrophic respiration, 15% greater CH4 uptake, and 44% lower N2O emission as compared with the other two agroforestry systems. Overall, the GWPm of greenhouse gas emissions was greater in hedgerow (88) and shelterbelt (85) than in the silvopasture system (76kgCO2ha(-1)). High GWPm in the hedgerow and shelterbelt systems reflects the greater contribution from the monoculture annual crops within these systems. Opportunities exist for reducing soil greenhouse gas emissions and mitigating climate change by promoting the establishment of perennial vegetation in the agricultural landscape.
authors.affiliation: Department of Renewable Resources, University of Alberta, 442 Earth Science Building, Edmonton, Alberta T6G 2E3, Canada.
authors.forename: Mark
authors.initials: M
authors.lastname: Baah-Acheamfour
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, 410 Agriculture/Forestry Centre, Edmonton, Alberta T6G 2P5, Canada.
authors.forename: Cameron N
authors.initials: CN
authors.lastname: Carlyle
authors.affiliation: Department of Renewable Resources, University of Alberta, 442 Earth Science Building, Edmonton, Alberta T6G 2E3, Canada.
authors.forename: Sang-Sun
authors.initials: SS
authors.lastname: Lim
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, 410 Agriculture/Forestry Centre, Edmonton, Alberta T6G 2P5, Canada.
authors.forename: Edward W
authors.initials: EW
authors.lastname: Bork
authors.affiliation: Department of Renewable Resources, University of Alberta, 442 Earth Science Building, Edmonton, Alberta T6G 2E3, Canada,. Electronic address: scott.chang@ualberta.ca.
authors.forename: Scott X
authors.initials: SX
authors.lastname: Chang
mesh_terms: D000383:Agriculture / Q000379:methods; D000393:Air Pollutants / Q000032:analysis*; D000416:Alberta; D058448:Biota; D002245:Carbon Dioxide / Q000032:analysis; D004784:Environmental Monitoring; D016468:Forestry / Q000379:methods*; D065928:Forests; D065948:Grassland; D000074382:Greenhouse Gases / Q000032:analysis*; D008697:Methane / Q000032:analysis; D009609:Nitrous Oxide / Q000032:analysis; D018517:Plant Roots / Q000378:metabolism; D012987:Soil / Q000737:chemistry
chemical_list: D000393:Air Pollutants; D000074382:Greenhouse Gases; D012987:Soil; D002245:Carbon Dioxide; D009609:Nitrous Oxide; D008697:Methane
keywords: Agriculture; Agroforestry; Canada; Climate change; Hedgerow; Shelterbelt; Silvopasture; Temperature sensitivity