| Climate warming is a global environment issue today, the main reason for this issue is the increasing concentration of greenhouse gases in atmosphere, and CO2 and N2O has been paid much attention due to their substantial contribution to global warming. The contribution of CO2 to climate warming is 65%. Although the contribution of N2O is only 5%, less than CO2 significantly, then the single molecule warming potential of N2O is 296 times than CO2. Meanwhile, the retention time of N2O in atmosphere is 120-150 years. In addition, the photolysis products of N2O in stratosphere can affect the photochemical process of O3. Therefore, N2O in atmosphere have a double bad effect and this impact has become increasingly evident.The main sources of CO2 are fossil fuel use and land-use change, while the main source of N2O is agricultural activity. It is easily find that agricultural production activity has enormous effect on the concentration of CO2 and N2O in atmosphere. Tillage is an important part of agricultural activity, and there is a significant difference of the emission of CO2 and N2O from farm ecosystem under different tillages. Compared with conventional tillage, no-tillage could optimize soil structure, increase soil moisture, reduce soil erosion, reduce farming costs and improve water use efficiency, etc. However, the effect of no-tillage on CO2 and N2O emission from farm has not clear.Based on the observation of CO2, and N2O emission from soil-crop ecosystems, seasonal variation characteristic, influences factors and seasonal change of NEE in rape season were discussed in this paper. CO2 and N2O emission were measured by static chamber-gas chromatographic techniques. The tillage experiment was established in the Key Field Station for Monitoring of Eco-Environment of Purple Soil of the Ministry of Agriculture of China, located in the farm of Southwest University (30°26′N,106°26′E), Chongqing. Four tillage treatments including conventional tillage with rice only system (DP), conventional tillage with rotation of rice and rape system (SH), no-till and plain culture with rotation of rice and rape system (XM), no-till and ridge culture with rotation of rice and rape system (LM)were selected as research objectives. Results were as following:(1) In rape season, the main CO2 source in farm ecosystem was soil respiration in DP which has no plant in this season, and the respiration rate was maintained at a low level. The change trend of respiration rate in other three treatments for the first and then decreased. With the rape growth, temperature recovery and the strength of other factors which could cause the strengthening of the ecosystem respiration, ecosystem respiration rate gradually increased. In the whole rape season, farmland ecosystem respiration under different tillage systems has no significant difference. At different growth stages of rape growth period, the total respiratory trends were similar under different tillage systems, the emissions order was flowering> pod maturity> seedling> moss bud.In rice seeding and tillering stage, the respiration rate under every tillage treatment was low and only increased in a small range. The respiration rate showed a rapid increase when entering the jointing stage when the rice growth rapid. The respiration rates of each treatment reached to the maximum value in flowering stage, the order was LM(2212.1±157.8)> XM(1909.9±402.2)> SH(1899.8±390.2)>DP (1760.7±62.8 mg CO2·m-2·h-1)。At last, the respiration Tage of each treatment declined due to the plants matured and leaves withered. There had no significant difference of the total ecosystem respiration rate in different treatments. In different rice growth stages, the total ecosystem respiration rate order was mature stage> heading and flowering> tillering> jointing> turning green stage.(2) NEE (net ecosystem CO2 exchange) seasonal change under different treatments had similar trend. Every treatment had different dynamics of above-ground biomass and root/shoot ratio and NEE with the rape growth. The amount order of carbon sequestration from atmosphere to crop ecosystem was LM(1.29±0.05)>XM(1.27±0.02)>SH (1.26±0.03 t C·hm-2),and carbon sequestration mainly occurred in the rape-growing stage.(3) The N2O emission mainly occurred in rice season in DP all year. Although the time percent of rice season only 27.35%, the amount percent of N2O emission reached to 54.47%. The N2O emission in each treatment in rape growth period had no significant difference. The amount of N2O emission in different growth stage showed "V" type, mainly concentrated in seedling stage and pod maturity.The N2O emission flux in every treatment fluctuations significantly strengthened in rice stage. The reduction effect of XM on N2O emission had been a marked expression in this stage. The cumulative emission order of N2O throughout rice stage was DP (3.81±1.64)>LM (3.73±1.43)> SH(2.58±2.31)>XM(1.17±1.72kg N2O·hm-2).(4) The application of no-tillage accelerated the total ecosystem respiration, the order of annual total respiration was XM(48.17±6.36)>LM(44.46±4.16)>SH(38.78±4.68)>DP(31.63±2.78 t CO2·hm-2). However, XM had a strong inhibitory effect on N2O, the annual emission order of N2O was SH(10.72±3.94)>LM(10.01±2.28)>DP(7.06±0.70)>XM(6.60±2.63 kg N2O·hm-2).(5) Temperature is an important effect factor on ecosystem respiration, while the effect on N2O emission is no significant. While the WFPS in rape season and the water depth in rice season had a certain influence on ecosystem respiration and N2O emission. The impact of a varoius factors on ecosystem respiration and N2O emission are not independent, but the result of joint action. Therefore, only consider the variety of factors at the same time, the effect of tillage on the change of CO2 and N2O could be estimated better.
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