Differences In The Characteristics Of CH₄Emission And Plant Characteristics Between Super-Rice And Traditional Rice Varieties

Paddy field is one of the most important anthropogenic source of atmospheric methane, which is the mainly greenhouse gas, and China paddies had larger methane emission among the world. The rice plant plays an important role in the production, oxidation and transmission of methane in paddy field. Root exudates and deposits’ composition and content of varieties are different, resulting in diversity of methane production among fields with different varieties. Rice plant influences the oxidation of methane via different root oxygen ability. The root oxygen ability stronger, the methane emissions of rice lower. Most of methane (more than90%) in paddy soil goes into the atmosphere through the aerenchyma of rice plant. Different rice cultivars have differences characteristics in root, plant height, tiller number and leaf physiological, which make diversity transmission and oxygen efficiency of methane production. In general, there were significant differences in the methane emissions among rice varieties. Super-rice varieties will be popularly sown in China due to their higher potential and the shortage of cropland area. Recently, researches about super-rice are focused on breeding, yield and quality formation, and physiological and ecological characteristics. It is important to determine whether the large scale application of super-rice varieties does indeed lead to a general increase in methane emission. Therefore, we conducted a pot experiment with super rice and conventional rice varieties which have representative and popularize area in the three major rice areas to study the differences in plant productivity and CH4emission between the varieties and to provide theoretical reference and technical support for super rice breeding and application, and rice cropping innovation for higher-yield with lower-emission.1. In all of the cultivars, two distinct methane emission peaks were detected; one at the max tillering stage, and the other at the heading stage. Mostly, the peak at the heading stage was lower than the peak at the max tillering stage; the peaks of super rice were lower than conventional rice’s. The cumulative methane emissions at whole growth period from conventional rice:Zhendao11, Fengliangyou6, Liangyou038, Liaojing9and Liaoyou5218was significant higher than that from super rice:Ningjing1, II you084, Wuyou308, Jijing88and Liaoyou1052to ca.35.22%(P<0.05),0.65%,25.68%(P<0.05),45.44%(P<0.05),5.87%, respectively. The difference in CH4emissions of conventional Japonica rice in the lower reaches of Yangtze River and Northeast was most evident. The methane emission differences among cultivars were significant at reproductive stage; and the rice plant has greatest impact on methane emissions at this stage, which were affected by many factors such as plant morphology, biomass, root system, and so on.2. Root was the main factors that made diversity CH4emissions of different varieties of Japonica rice. There was no difference in aboveground biomass, leaf areas and plant height between Japonica super-rice of Yangtze lower reaches Ningjing1and conventional rice Zhendao11, whereas methane emission and dissolved methane concentration from Zhendao11were significant higher than those from Ninjing1, owing to significant difference between root system. Especially at heading stage, the root dry weight were significant higher than that of Zhendao11by44.83%. This study indicated that the cultivar with stronger root system may reduce methane emission. Methane emission from Japonica super-rice Jijing88was lower than that of conventional rice Liaojing9by82.95%(P<0.01) at reproductive stage; while its root dry weight were higher than that of Liaojing9by93.03%(P<0.05). Differences values of root dry weight between the two varieties were significantly higher than that of plant height and leaf area. This study suggested that the reductions of CH4emissions are mainly due to the significant increases in rice root biomass. At the same time strong root system can enhance leaf photosynthesis and dry matter production at ripening stage. The gain yield of Ninjing1and Jijing88was higher than that of Zhendao11and Liaojing9by35.0%(P<0.05) and67.28%(P<0.05), respectively. Therefore, maintaining a strong root system is not only conducive to increasing rice yield, but also to promoting the methane emission reduction.3. Maintaining plant vitality of Indica rice at ripening stage to increased harvest index not only can increase the yield, but also conducive to reducing CH4emission. There’s no differences between total methane emissions of Indica hybrid rice of Yangtze lower reaches:Ⅱ you084and Fengliangyou6, while grain yield, harvest index of Fengliangyou6were significantly higher than those of Ⅱ you084. Finally, the yield-scaled CH4of Fengliangyou6was significantly lower than that of Ⅱ you084by22.00%(P＜0.05). Therefore, under the same yield target, even if area-scaled methane emissions were consistent, CH4emission from higher-yield rice will be reduced. Methane emission from Indica conventional rice of Yangtze upper reaches Liangyou038was significantly higher than that of super rice Wuyou308at vegetative and reproductive stages. Although CH4emission of Wuyou308was a littler higher at ripening stage, its total CH4emission was lower than that of Liangyou038. And grain yield, harvest index of Wuyou308were significantly higher than those of Liangyou038, so the yield-scaled CH4of Fengliangyou6were significantly lower than that of Ⅱ you084by28.81%(P＜0.05). The results indicate that maintaining plant vitality to promote dry matter production and grain filling at later stage, and slowing the aging process, not only can increase the yield, but also reduce CH4emission.