| The increasing concentration of greenhouse gases in the atmosphere, such as CO2, CH4 and N2O has been paid much attention due to their substantial contribution to global warming and ozone depletion, the two severest impacts on the global climate. Agroecosystem plays an important role in the budget of atmospheric greenhouse gases. It is important to investigate the effect of management regime on greenhouse gases emission from agroecossytems, as the information is the base of compiling the inventory of greenhouse gases emission and the precondition of drawing relevant policies to mitigate greenhouse gases emission.In order to examine the effect of management regime, such as nitrogen application, planting regime and plowing method, on soil respiration, N2O and CH4 emissions from farmland, the static opaque chamber-gas chromatograph method was used to simultaneously measure CO2, N2O and CH4 fluxes in situ. The field measurement was carded out for three years. The effect of nitrogen application on soil respiration, N2O and CH4 emissions was investigated during 2002-03 rice-wheat rotation period. The effect of planting regime and plowing method on soil respiration, N2O and CH4 emissions was investigated during 2003-04 maize/soybean/rice-wheat rotation period. And the effect of plowing depth and planting regime on soil respiration, N2O and CH4 emissions was investigated during 2004-05 maize/rice-wheat rotation period.Root regression technique was used to partitioning the components of soil respiration in a wheat-planted soil for examine the factors influencing root respiration.By compiling the in-situ measurement data of soil respiration and relevant climate and soil information, the temporal and spatial variations in soil respiration from Chinese terrestrial ecosystems and their controlling factors were investigated. Based on a stepwise regression analysis, annual soil respiration was modeled by the climate and soil factors.The results are as follows:1. Fertilizer nitrogen application enhanced soil respiration and N2O emission, while it decreased CH4 emission. Soil respiration increased in fertilizer-applied treatments compared with no fertilizer treatment after three times of fertilizer application on 9 November 2002, 14 February and 26 March 2003. And the most obvious increase was found following the third fertilizer application. No significant difference in soil respiration was found among several fertilizer application treatments. Direct N2O emission factors for wheat farmland and rice paddy were 1.68% and 1.10%, respectively. The relationship between annual N2O emission and nitrogen input could be explained by a linear regression function, with a direct N2O emission factor of 1.22%. Significant higher CH4 emission was found in a rice paddy where 150 kg N.hm-2 was applied compared with that in the treatment where 450 kg N'hm-2 was applied.2. There is significant difference (P<0.001) not only in soil respiration but also in N2O emission among three farmlands planting maize, soybean and rice. The highest soil respiration rate was appeared in maize plot, while the soil respiration was lowest in rice paddy. The seasonal mean soil respiration rates for maize plot, soybean plot and rice paddy were 168.3,123.6,72.6 mg C.m-2.h-1, respectively. These is also significant difference (P<0.001) in N2O emission among three farmlands planting maize, soybean and rice, while the highest to lowest N2O emission was for maize plot>rice palddy>soybean. The seasonal mean N2O fluxes for maize plot, soybean plot and rice paddy were 59.4,231.9,68.3μg N.m-2.h-1, respectively. In the plot planting winter wheat, seasonal N2O emission could be simulated with wheat yield with an exponential function (R2=0.84, P<0.001, n=18). Moreover, the relationship between seasonal N2O emission and above ground biomass could also be modeled with an exponential function (R2=0.87, P<0.001, n=18).3. Deep plowing (25 cm) increased soil respiration compared with no plowing (0 cm) and there is no significant difference of N2O emission among different plowing treatments. Field observations indicate that in each cropping season the seasonal variation of soil respiration was developed with the similar pattern for different treatments. In the plots where preceding cropping practice was rice paddy, deep plowing (25 cm) greatly enhanced CO2 evolution from soil compared with no-till treatment in 2004-05 wheat season. Generally, for our investigation, soil respiration was not significantly different for the shallow plowing (12 cm) and no-till (0 cm) practice. No significant difference of N2O emission between different plowing practices, when the same preceding cropping practice was considered. It can also be found that crop yield was generally higher for shallow plowing (12 cm) treatments.4. Soil respiration and gross nitrification in wheat field generally decreased with the increase of soil depth, and the viriation of soil respiration and gross nitrification could be well explained by root biomass. Plowing practice enhanced soil respiration in surface soil of 0～7 cm but had no significant effect on gross nitrification and denitrification. Cropping system affected soil gross nitrification. Gross nitrification in the plot with preceding crop of paddy rice was higher than that with maize. Nitrification rather than denitrification played a key role in nitrogen transformation and N2O production in wheat field where urea was used as nitrogen fertilizer. The variations of soil respiration and gross nitrification rates can be quantitatively described by root mass with exponential functions.5. Soil temperature and moisture were the two main factors controlling the seasonal variations in soil respiration from dry farmland and in N2O emission from soybean and maize lands. A statistical function involving the two factors explained about 54.1% seasonal variations in soil respiration. Root growth enhanced soil respiration. The variation of root nitrogen content and soil moisture could explain about 96.6% variation in root respiration coefficient. The seasonal variations of N2O flux were mainly drived by soil moisture and temperature in maize and soybean plots, while soil temperature, moisture and leaf are index (LAI) were the three main factors influencing the seasonal variations of N2O flux in winter wheat-planted farmland.6. Our statistical analysis of reported data indicated that temporal and spatial variations in soil respiration rates from terrestrial ecosystems in china were controlled by annual mean air temperatures, annual precipitation and surface (20 cm) soil organic carbon (SOC) content. Annual precipitation tended to be the single best predictor of annual soil CO2 flux when all the measurements were used for statistical analysis (R2=0.44, P<0.001, n=86). And annual mean air temperature could explain about 30% variations in soil respiration (R2=0.30, P<0.001, n=86). Soil nitrogen tended to be a key factor of influencing soil respirtation in farmland or grassland ecosystem, while this phenomenon was not obvious for forest ecosystem. A stepwise linear regression model (R2=0.67, P<0.001, n=86) including annual total precipitation, annual mean air temperature and surface SOC well explained the temporal and spatial variation of soil respiration across different ecosystems.For our study, seasonal N2O emission correlated not only with nitrogen application but also with crop production, as crop yield and biomass increased with nitrogen application and also influenced by management regime. In the winter wheat farmland, crop production tended to be better index to simulate seasonal N2O emission than nitrogen application. From our study we can also found that in the wheat farmland where preceding cropping practice was rice paddy, conservation tillage practice (0 cm plowing) reduced soil CO2 emission compared with deep plowing (25 cm plowing), but not increase N2O emission. Furthermore, our investigation confirmed that not only climate factors of precipitation and temperature but soil organic carbon content influenced the temporal and spatial variations in soil respiration from Chinese terrestrial ecosystems.In conclution, fertilizer nitrogen application enhanced soil respiration and N2O emission, while it decreased CH4 emission. There is significant difference not only for soil respiration but also for N2O emission among three farmlands planting maize, soybean and rice. Deep plowing increased soil respiration compared with no plowing, and there is no significant difference of N2O emission among different plowing treatments. Soil respiration and gross nitrification in wheat field generally decreased with the increase of soil depth. Annual mean air temperatures, annual precipitation and surface soil organic carbon contentcontrolled the temporal and spatial variations of soil respiration rate from terrestrial ecosystem in china.
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