Greenhouse Gases Emissions From Different Land Use Types And Their Global Warming Potential At Xianning, Hubei, China

Greenhouse Gases (GHGs) emissions from agroecosystem had attracted more attention nowadays. To better understand the influence of GHGs from agroecosystem on global environment and provide the basis for reasonable management of agroecosystem, Carbon dioxide, Methane and Nitrous oxide fluxes and their influence factors were studied by closed chamber-Gas Chromatography method under different land use types (Upland, Forest, Orchard and Paddy fields) at Xianning, Hubei. The results were as follows:1. With the mean flux from 55.99 to 85.58mgC·m^-2·h^-1, soil CO₂ flux under four land use types ranged from 6.37 to 230.74 mgC·m^-2·h^-1, which showed the same seasonal fluctuations, with the highest in summer, higher in spring and autumn and lower in winter except for paddy soil. The order of average soil CO₂ flux was: Paddy field＞Orchard＞Upland＞Forest. Soil CO₂ flux was highly correlated with temperature in 5cm soil depth and there were no significant correlations between soil CO₂ fluxes and soil moisture.2. Soil CH₄ flux ranged from-0.16 to 23.26 mgC·m^-2·h^-1, with the mean flux from-0.02 to 3.64 mgC·m^-2·h^-1. The order of annual soil CH₄ flux was: Paddy field＞Upland＞Orchard＞Forest. Upland, Forest, Orchard and Rape fields absorbed CH₄ and Paddy fields emitted CH₄. There were no significant correlations between soil CH₄ fluxes and soil temperature in 5cm depth, soil moisture.3. Soil N₂O flux ranged from-0.75 to 88.95μgN·m^-2·h^-1, with the mean flux from 10.07 to 20.85μgN·m^-2·h^-1. The order of average soil N₂O flux was: Paddy field＞Orchard＞Upland＞Forest. Soil N₂O flux from different land use types showed the same seasonal variations,with the highest in summer, higher in spring and autumn and lower in winter. Even Soil could absorb N₂O in winter. There were correlations between soil N₂O flux and soil temperature in 5cm depth except Paddy fields but soil N₂O flux had no correlations with soil moisture.4. The different Nitrogen treatments experiments at rape fields showed that: The more nitrogen fertilizer applied, the more soil CO₂ flux increased apparently. However, soil CO₂ flux was not linear increase. In addition, the more nitrogen fertilizer applied, the less CH₄ absorbed and the more N₂O emitted for the rape fields.5. The order of total Global Warming Potential (GWP) of different land use types was: Paddy field＞Orchard＞Upland＞Forest. And the Global Warming Potential was 1.8×10⁴, 1.7×10⁴, 2.1×10⁴, 3.5×10⁴kg eCO₂·hm^-2·a^-1, respectively. The more fertilizer applied, the more total GWP was.6. Xining area will get warmer in future due to the variations of GWP by land use changes or soil management.