| CH4 is one of the main greenhouse gases, with importance second only to CO2. Ricepaddies are an important human-made ecosystem for the global CH4 budget. Methane transportcan occur via diffusion, gas bubble release and via the aerenchyma of rice plants. Of the threepathways, Over 90％CH4 emitted to the atmosphere through aerenchyma transport, which isconsidered the most important when rice plants are involved in the ecosystem. Therefore, it iscrucial to research the correlation between methane emission from paddy soil and plantaerenchyma tissues. To understand the relationship is useful for breeding rice varieties with highyielding and low methane emission, as well as by culture measures influence rice plantaerenchyma to reduce methane emission from paddy soil. In addition, with the area of directsowing rice and high yielding rice cultivars increasing, especially super hybrid rice cultivarsbreed and spread quickly, it is vital to measure their methane emission flux and it is full of praxissignification to provide the environmental basis for direct sowing rice and super hybrid ricedevelopment.CH4 of 39 rice cultivars, including the conventional rice, hybrid rice and super hybrid ricewere determined using the static chamber technique and calculated the amount of methaneemission in the whole season and averaged seasonal methane emission flux. Then methaneemission from the different culture methods were conducted, including translating rice (TR),broadcast sowing rice (BSR), drill rice (DR) and hole sowing rice (HSR) and the differences ofmethane emission were analyzed. In the rice-duck complex ecosystem, the optimal number ofducks was confirmed to gain the objective of increasing the economic benefits and reducing theenvironmental cost on the base of comprehensive consideration the rice production, economicand environmental benefits. The main results were as follows.1. The differences of methane emission among rice cultivars were significant. Methane ofthe conventional early rice Xiangzaoxian No.12 was 1.42 times higher than that of ChenzaonuNo.1 and for hybrid early rice, Jinyou No.706 was 1.17 times higher than that of Weiyou No.402.The highest methane emission of late rice cultivars was Yuchi231-8, which was 1.35 timeshigher than that of Xiangwanxian No. 12, and for hybrid late rice, Tyou259 was 1.24 times higherthan that of Jinyou No.207. Methane emission differences were significant between theconventional rice and hybrid rice as the same as between non-glutinous rice and Indicia type rice. Methane emission amount of early and late conventional rice were by 3.66g/m2, 0.68 g/m2 morethan that of hybrid rice, respectively. Therefore, CH4 emission of hybrid rice is lower than that ofthe conventional rice.2. Aerenchyma tissues of plant culms above ground were observed and the correlationshipsbetween aerenchyma characteristics and methane emission were analyzed. The results showedthat the significant relativities existed in methane emission and many quantitative indexes ofplant tissues, such as the highest internodes plant diameter, stem vascular bundles area, stem wallthickness and the area ratio of sheath transverse section and internodes transverse section of thesecond internodes during early rice season. During late rice season, the correlation between plantheight and methane emission was significant at 0.001 level. The area ratio of sheath transversesection and internodes transverse section, the area ratio of stem vascular bundle and stem walltransverse section of the third internodes, the area ratio of all vascular bundles and internodestransverse section of the second internodes, the area ratio of all the vascular bundles and stemwall transverse section, the area ratio of all the sheath vascular bundles and stem wall transversesection of the highest internodes, which were significant correlation with methane emission at0.01 levels. In addition, 17 quantitative indexes from the highest internodes to the fifthinternodes were significant with methane emission at 0.05 levels.With above mentioned correlative indexes, fuzzy clustering analysis method was applied tothe methane emission amount of rice cultivars of early and late rice. The consistent degrees ofclustering results with measured results of early and late rice were 87.5％, 90％, respectively. Itwas showed the clustering indexes were appropriate in distinguishing methane emission of ricecultivars to high, medium and low type. The principal component analysis method was applied tothe correlation factors of plant tissues and methane emission, the main factors of plant height,vascular bundles, air chambers and stem wall were determined and by the four main factors,clustering the cultivars with methane emission, the consistent degree was 83.3％comparing withthe observed results.To further analysis on the correlation between methane emission and rice rootcharacteristics, root biomass, volume, number of white roots, root activity, root total absorbingarea and active absorbing area all presented the significant positive correlation with methaneemission. Therefore, it can be concluded that rice root characteristics impacted methane emissionvia rice plant aerenchyma system largely.3. Analyzing on the correlation between rice leaf stoma and methane emission flux, theearly rice flag leaf stomata density and the stomatal number were significant positive correlationwith methane emission flux at the booting stage and for late rice cultivars, the number of thesecond leaf stoma of the conventional rice were significant correlation with average seasonal methane emission flux at 0.05 levels, and the number of the third leaf stoma, with the bootingstage methane emission flux at 0.05 level, the number of up three leaves stoma with bootingstage methane emission flux at 0.01 level.To late rice cultivars, total flag leaf stomata area was significant negative correlation withmethane emission flux at the full heading stage.However, total stomata area of the second leafwas significant positive correlation with methane emission flux at the full heading stage. TheDSR flag leaf stomata density and the total number of stoma presented significant negativecorrelation with methane emission flux at the early heading stage. Therefore, it was affirmativethat rice leaf stomata characters were correlative with methane emission and leaf stomatainfluenced methane emission from paddy field through plant aerenchyma tissues. This resultproved the viewpoint that rice leaf stoma opening and closing impacted the daily variationpattern of methane emission.4. Based on the methane emission from paddy field during rice growth stages,thedifferences of amount methane emission were significant between direct sowing rice(DSR) andtranslating rice(TR), as well as among three direct sowing methods. There existed manydifferences in sowing date, growing days in the field and growth stages between DSR and TR.So, difference of methane emission existed in the same days or in the same stage, which resultedin without comparison in methane emission between DSR and TR at the same time. In thisexperiment, methane emission fluxes of different cultural methods were measured at the intervalof three days and total amount methane emission calculated by the Inner-integral-sum method.Then the average values in the whole season were figured out by the growth days. It was feasibleto compare their amount of seasonal methane emission and average seasonal methane emissionflux of DSR and TR.The results showed that the seasonal average CH4 flux of direct sowing rice were lower thanthat of translating rice. However, amount CH4 emission of DSR was more than that of TR.Amount CH4 emission of TR reduced by 1.24 g/m2 comparing with DSR and by 1.02 g/m2 in2005 early and late rice respectively. Amount CH4 of the conventional early TR was low by 7.5％,and super hybrid TR was reduced by 3.8％in 2006 early rice. Amount CH4 emission of TR werereduced by 28.9％, 54.3％, 34.1％comparing with the broadcast sowing rice with the density of 80seedlings/m2 (BSR), drill rice with the density of 80 seedlings/m2 (DR), hole sowing rice with 2seedlings per hole(HSR), respectively. The significant differences also existed in differentbroadcast rice densities or hole sowing densities, moreover, more density, higher methaneemission flux. In addition, methane emission of unit rice yielding of DSR was more than TR. In2006 late rice, methane emission of unit rice yielding of DSR was 37.62 g CH4/kg rice, andenhanced 17.7％comparing with that of TR. During 2006 early rice, methane emission of unit rice yielding of the conventional DSR enhanced by 4.84 g CH4/kg rice more than that of TR, forsuper hybrid rice, DSR increased by 3.48 gCH4/kg rice higher than that of TR and theconventional rice was higher than the translating rice either DSR or TR method.Based on the methane emission of the DSR and TR in the same area and days, during earlyrice season, Comparing the total amount of methane emission and average CH4 emission, theconventional DSR was the bggest and second to the conventional TR, next to the super hybridDSR and the super hybrid TR was the less.The methane emission of unit rice yielding for DSRwas higher than the TR and the conventional rice was higher than the super hybrid rice.Synthetically considering rice production and methane emission, the density of 80 seedlings/m2and 4 seedlings/hole were the optimal patterns.5. CH4 emission fluxes among different number of ducks existed significant differences inthe rice-duck ecosystem. Dissolution oxygen content of the water body and soil were increasedas result of ducks activities and looking for food, which resulted in number of methanogenicbacteria lower significantly at the maximum methane emission stage. A t the same time, ducks inthe fields controlled the inefficacy tiller numbers, reduced number of withered leaves. Therefore,methane emission flux reduced significantly with the conventional culture rice. Number ofmethanogenic bacteria under 20 ducks per 667m2 treatment paddy soil was reduced by 38.9％～51.6％in early rice and by 69.8％～90.2％in late rice comparing with that of non-ducks paddysoil. Comparing with the non-ducks paddy soil, during early rice, the redox matter, the activeredox matter and the active organic matter were lower at the range of 0.322～1.118,0.239～0.689, 0.203～0.548 c mol kg-1, and for the late rice 0.171～0.628, 0.220～0.591, 0.157～0.433c molkg-1, respectively. Therefore, amount methane emission of 10ducks per 667m2, 15ducks per667m2, 20ducks per 667m2 were reduced by 18.2％, 26.1％, 28.1％during early rice and for laterice, were17.7％, 27.6％, 34.4％comparing with that of non-ducks rice soil, respectively.Moreover, ducks were more in the field, dissolution oxygen content in the water body werehigher, but number of methanogenic bacteria in paddy soil and soil redox matter content werelower, which resulted in lower CH4 emission flux.Environmental and economic benefits analysis showed that more ducks in the rice-duckecosystem resulted in more economic benefits. The net incomes of 10 ducks per 667m2, 15 ducksper 667m2, 20 ducks per 667m2 increased by 2644 yuan/hm2, 2830 yuan /hm2, 3006 yuan/hm2, respectively and environmental economic benefits increased by 2986 yuan/hm2, 3197yuan/hm2, 3390 yuan/hm2 more than that of non-ducks paddy fields, respectively. Comparingwith the conventional culture rice yielding, the treatment of 20 ducks per 667m2 impacted ricegrowths and development, reduced rice yielding significantly, and that 10 ducks per 667m2treatment enhanced rice yielding. 15 ducks per 667m2 treatment did not influence rice growth and development, at the same time its environmental and economic income was more than 10ducks per 667m2. Rice paddy must give priority to rice production and add other affixationvalues in order to increase economic benefit in the premise of ensuring rice production.Therefore, synthetically considering rice production, environmental and economic benefits, 15ducks per 667m2 was the optimum pattern in the rice-duck ecosystem.6. This thesis was analyzed the correlation between soil characteristics and methaneemission in the rice-duck ecosystem. Firstly, the significant correlation existed between the soilredox matter content and methane emission flux. The linear regression equation between the totalredox matter(X) and methane emission flux(Y) was Y=2.1138X+1.7552 and their relativity weresignificant at 0.05 level(R=0.8397), and for soil active redox matter(X), active organic redoxmatter(X) were Y=3.6161X-0.3435, Y=5.9046X+1.9865, respectively, and their relativities weresignificant at 0.01 levels(R=0.9250, 0.9208), respectively.Secondly, the significant negative correlation between water body dissolution oxygencontent and methane emission flux. The regression equation between methane emission(Y) anddissolution oxygen content(X) was Y=-1.5276X+14.7707, and their relativity were significant at0.001 level (R=-0.9390).Thirdly, the significant positive correlation existed between methane emission flux andnumber of soil methanogenic bacteria. During early rice, the regression equation between CH4emission flux (Y) and number of methanogenic bacteria(X) was Y=11.4949+0.5088X, and laterice was Y=12.9218+0.0558X, and their relativities were significant at 0.001 level (R=0.7798,0.8037, respectively). During early and late rice, the number of soil methanogenic bacteria variedconsistently with methane emission flux variation from paddy soil. Therefore, soil methanogenicbacteria were important factor to control methane production and emission.The results showed that the ducks activities added the dissolution oxygen content of waterbody, reduced number of methanogenic bacteria and soil redox matter content, which resulted inlower methane emission flux significantly. Withal more ducks, higher dissolution oxygen content,lower number of methanogenic bacteria and redox matter content. Therefore, amount of CH4production reduced and methane oxidation increased, then methane emission flux was lower.
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