| Nowdays, global warming and stratosphere ozone depletion caused by the increasing concentrations of atmospheric greenhouse gases are the globlal emvironmental issues. Beside CO2,.CH4 and N2O are considered as the other two most important GHGs, and their emissions are the results of production, consumption and transformation in soil profile. Therefore, the concentrations of CH4 and N2O in soil profiles are characterised by temporal and spatial heterogeneity. Paddy ecosystem has been recognized as the major sources of these GHGs, and different paddy-upland rotation systems are adopted. Thus, an investigation of GHGs effluxes in soil profiles under different rotation systems is of great importance.In this study, the concentrations of CH4 and N2O in the soil profile at four different depths (7cm,15cm,30cm and 50cm) were monitored through in situ gas collection system under different rice-upland crop rotation systems, and the objective was to investigate the temporal and spatial variations of the concentrations of CH4 and N2O and their efflux patterns. Two different rotation systems, single rice-wheat (R-W) and double rice-rape rotation (D-R), were estbalished as the main factor. For each rotation regime, four treatments with three replications were included, namely, control (N0S0), N fertilizer without straw (N1S0), N fertilizer with low level straw (N1S1) and N fertilizer with high level straw (N1S2).Results showed that CH4 in the soil profile mainly produced in the rice growing season under flooded conditions, while was substanitially small during both the wheat and rape growing seasons across all the depths. CH4 concentrations in the subsoil (30 cm and 50 cm) were much higher than in the surface soil during the wheat growing season. During the rape growing season, CH4 concentrations were dependent on soil depths. During the rice growing season, CH4 mainly produced in the surface soil (7cm and 15cm), and decreased with increasing soil depth with the order of 7cm?15cm?30cm?50cm.N fertilization significantly increased CH4 concentrations in single and double rice seasons as well as the rape season (p<0.05), while marginally increased CH4 concentrations in the wheat season. N fertilization combined with straw application increased CH4 concentrations across all layers during the wheat seasons, as well as significantly increased in the subsoil during the single rice season (p<0.05). High level straw application contributed to significantly enhanced the CH4 concentrations across all layers during both the double rice and rape season.The CH4 fluxes appeared positive peak in the 0-7cm, but negative peaks in 7-15cm during the rice growing season, respectively. During the rice growing season, the diffusion of CH4 mainly occurred in the surface soil (0-7cm and 7-15cm) with the direction from production zone to the deeper layer. Seasonal dynamics of the CH4 fluxes in the 0-7cm varied significantly, and both the positive and negative values of CH4 were recorded in 0-7cm and 7-15 cm, respectively. In the 0-7cm CH4 fluxes were positive, but were negative in other soil profiles, which were mainly caused by the value of CH4 concentrations in the two soil layers.Over the two cycles of rice-upland crop rotation sysytems, N2O concentrations in the soil profile showed significant spatial and temporal distribution patterns across all treatments. The peaks of N2O concentration occurred during the early growth stages for all the crops, and N fertilization significantly increased the value of the peak. while straw application reduced the size of the peak, but did not affect the dynamics. N2O production mainly focused in the subsoil (7cm and 15cm) during the rice season, being in the sequence of 15cm?7cm?30cm?50cm, while it was mainly ocurred in the near subface at the depths of 30cm and 50cm during the upland crop season. N fertilization significantly increased the N2O concentrations across all layers during all the corp seasons (p<0.05). In contrast, N fertilization combined with high level straw application significantly reduced N2O concentrations in the near surface soil layers during all the crop seasons (p<0.05).Seasonal dynamics of the fluxes of N2O exihited greater fluctuation in the surface soil (0-7cm and 7-15cm), while it was gentle. The N2O fluxes in the 0-7cm were much higher than in the 7-15 cm. Straw application can reduce the surface N2O flux across all crop seasons.There was a significantly positive correlation between the CH4 fluxes in the 0-7cm and CH4 fluxes from the surface (flux from the soil surface to the atmosphere) in the rice crop season, while the CH4 fluxes in the 0-7cm were slightly lower than CH4 fluxes from the surface in both years. In addition to the growth of rape in 2010 year, the N2O fluxes in the 0-7cm and N2O fluxes from the surface also showed a significantly correlated relationship during the rice-upland crop rotation sysytem. The N2O fluxes in 0?7cm were significantly higher than the fluxes from the surface in both the rice and rape seasons, while it was oppsite during the wheat season. |
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