| The forests in mid-and high-latitudes experience a long non-growing season, during which the emission or consumption of such greenhouse gases as CO2, CH4 and N2O by the forest soils plays an important role in ecosystem carbon and nitrogen budgets. However, quantification of these trace gases in non-growing seasons has been scarcely conducted. In this study, we examined temporal dynamics of soil CO2, CH4 and N2O effluxes and their controlling factors for four representative temperate forests in northeastern China with a static closed chamber and gas chromatograph technique. These forests were Korean pine (Pinus koraiensis) plantation, Dahurian larch (Larix gmelinii) plantation, Mongolian oak (Quercus mongolica) forest and hardwood broadleaved forest (dominated by Fraxinus mandshurica, Juglans mandshurica, and Phellodendron amurense). Six static chambers (40cm×50cm×50cm) were randomly installed in each forest type. From early November of 2008 to May of 2009, gas samples were collected and analyzed every 1-2 weeks in non-growing(16 times in total non-growing seasons), and once a month in growing seasons(6 times in total growing seasons) The results showed that all forest soils were overall atmospheric CO2 source, N2O source and CH4 sink during the non-growing season. The mean values of soil CO2 efflux in the non-growing season were 65.5±8.1 mg m-2h-1(mean±standard deviation),70.5±10.2 mg m-2h-1,77.1±8.0 mg m-2h-1, and 80.5±23.5 mg m-2h-1 for the pine plantation, larch plantation, oak forest, and hardwood forest, respectively; those of soil CH4 efflux were-17.2±4.6μg m-2h-1 (negative values represent sink),-15.4±4.2μg m-2h-1,-31.5±4.5μg m-2h-1,and-23.6±4.1μg m-2h-1,respectively; and those of N2O efflux were 19.3±5.1μg m-2h-1,11.5±2.5μg m-2h-1,16.4±4.0μg m-2h-1, and 14.4±5.4μg m-2h-1, respectively. The soil CO2 efflux remained fairly low until the spring soil thawing started when the soil CO2 efflux increased with soil temperature increasing. Also we observed a spike of soil CO2 emission during the vernal soil thawing period in all forest types except for the hardwood forests. There was a significant exponential relationship between soil CO2 efflux (P<0.001). The soil CH4 efflux was negatively correlated with soil temperature (P<0.001). The soils were a net CH4 source in the mid-winter for all forests, but the source strength, occurring time and duration changed with forest types. The largest mid-winter CH4 source was observed in the Korean pine plantation (43.6μg m-2h-1). The temporal variability of soil N2O efflux was relatively great among the forest types. All forest soils emitted N2O during the spring soil thawing period, but the maximum efflux and its occurring time varied with the forest types. The soil N2O efflux was positively correlated with soil water content between 0-10 cm depth for all forests except for the pine plantation(P<0.01). All forest soils were overall atmospheric CO2 source and CH4 sink during the growing season. The mean values of soil CO2 efflux in the growing season were 213.9±24.5 mg m-2h-1 (mean±standard deviation),216.5±18.1 mg m-2h-1,293.2±23.1 mg m-2h-1,and 349.8±25.8 mg m-2h-1 for the pine plantation, larch plantation, oak forest, and hardwood forest, respectively; those of soil CH4 efflux were-66.0±4.8μg m-2h-1 (negative values represent sink),-84.2±6.8μg m-2h-1,-81.6±5.0μg m-2h-1, and-76.0±5.4μg m-2h-1, respectively. There was a significant correlated positive relationship between soil CO2 efflux (P<0.05). The soil CH4 efflux was negatively correlated with soil temperature (P<0.05).This study illustrated that the significant contribution of soil CO2, CH4 and N2O effluxes in non-growing seasons to annual emission or consumption of these greenhouse gases in the temperate forests, and calculated the annual flux of CO2, CH4 in these four temperate forests.
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