【作者】 张军科；

【导师】 江长胜； 王定勇；

【作者基本信息】 西南大学 ， 环境科学， 2011， 硕士

【摘要】 气候变暖是当今全球性的环境问题,其主要原因之一是由于大气中温室气体浓度的不断增加,其中CO2和N2O被认为是两种非常重要的温室气体,两者对全球变暖的贡献分别为65%和5%。虽然N2O的贡献较低,但其单分子增温潜势却是二氧化碳的296倍,且在大气中的停留时间长达120-150年；同时,N2O在平流层中的光解产物还能影响到O3的光化学过程,对全球环境和气候有着双重危害作用,而且这种影响越来越明显。农业生产活动对这两种温室气体在大气中的含量有着重要影响。其中,耕作方式是农业生产的重要部分,不同耕作方式对农田生态系统中温室气体的产生与排放有着较大差异。相对于传统耕作,免耕具有优化土壤结构、增加土壤水分、减少土壤侵蚀、降低耕作成本和提高水分利用效率等优点,然而,这种耕作方式对农业生产中CO2和N2O排放的影响还没有明确的结论。本研究以位于西南大学农业部重庆紫色土生态环境重点野外科学观测试验站于1989年设立的长期免耕试验田为研究对象,利用静态箱-气相色谱法研究冬水田平作(DP)、水旱轮作(SH)、厢作免耕(XM)和垄作免耕(LM)等不同耕作制度下紫色水稻土种植系统中生态系统总呼吸和N2O的排放进行了研究；对油菜季SH、XM和LM三种耕作方式农田NEE动态进行了考察,并分析了温度和水分两种主要的环境因子对生态系统总呼吸和N2O排放通量的影响。结果表明：(1)在油菜季,没有种植作物的DP处理中,农田生态系统总呼吸始终维持在一个较低水平,且变化不大；而其他三种处理中,油菜季的生态系统总呼吸速率变化总趋势为先升高后降低,随着油菜植株的生长和温度的回升以及其他有利于生态系统呼吸因素的加强,生态系势,排放量顺序都为花期>角果成熟期>苗期>苔蕾期。在水稻季的苗期和分蘖期,由于水稻植株较小且温度相对较低,各耕作方式下生态系统总呼吸速率呈现出较小范围的升高；进入拔节期后,随着水稻的快速生长,农田中生态系统总呼吸速率也呈急剧增长,并在花期达到较大的排放量,各处理的最大呼吸速率分别为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)。随着水稻的成熟和植株的衰老,生态系统总呼吸速率又呈下降趋势。在整个水稻季,各处理的CO2排放量整体上没有显著差异(p>0.05)。在水稻的不同生长阶段,生态系统总呼吸量为灌浆完熟期>抽穗扬花期>分蘖期>拔节期>返青期。(2)对油菜季NEE季节变化动态研究表明,只有在苗期前期和油菜生长的最后阶段表现出净的碳排放,而在大多数时期,油菜-土壤系统表现为净的碳固定。整个油菜生长季,各耕作方式下碳的固定为LM(1.29±0.05)>XM(1.27±0.02)>SH(1.26±0.03 t C·hm-2),免耕方式的应用对油菜-土壤系统的固碳能力有着一定的提高。(3)在DP处理中,全年的N2O的排放主要集中在水稻生长季,虽然水稻期的时间只占总采样期的27.35%,但其总排放量占年总排放量的54.47%。在油菜生长期内,三种种植作物的处理在不同时期分别表现为对N2O的吸收和排放,呈上下波动,但总体上表现为N2O的排放。通过单因素方差分析,各处理在整个油菜季的排放通量没有明显差异(p>0.05)。油菜的不同生长阶段的N2O排放量呈“V”型,主要的排放集中在苗期和角果成熟期。在水稻阶段,各处理N2O的排放通量的波动明显加强,XM处理对N2O的减排作用已经有了明显的体现,在整个研究阶段各处理的N2O累积排放量为DP(3.81±1.64)>LM(3.73±1.43)>SH(2.58±2.31)>XM(1.17±1.72 kg N2O·hm-2)。(4)通过对全年不同耕作方式下农田中生态系统总呼吸和N2O排放量的计算可以得出,免耕方式的应用加速了生态系统总呼吸,各处理全年总呼吸量为XM(48.17±6.36)>LM(44.46±4.16)>SH(38.78±4.68)>DP(31.63±2.78 t CO2·hm-2)；而XM处理对其中N2O的排放有着较强的抑制作用,各处理N2O的年排放量为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)温度是影响生态系统呼吸的重要因素(p<0.05),而对N2O的排放没有较显著的影响(只有极个别的温度与N2O的排放达到显著),同时油菜季的WFPS(土壤充水孔隙度,water-filled porespace,简称WFPS)和水稻季的水深对生态系统呼吸和N2O的排放也有着一定影响；各种影响因子对两种温室气体排放的影响不是独立作用的,而是共同作用的结果,因此,只有将各种影响因素同时考虑,才能更好地解释农田中两种温室气体的变化。更多还原

【Abstract】 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.更多还原