Methane Emission From Paddy Field In Different Rice Cultivars And Its Possible Mechanisms

Rice is one of the most important crops in China. Continuously increasing the rice yield has been one of the main objectives of grain production in China. At the same time, the methane emission from paddy field plays an important role in the global methane emission, and has an important contribution to the global greenhouse effect Study on the methane emission difference in different rice cultivars and elucidate the microbiological mechanism is vital to rice high yielding cultivation and methane reduction.In the present study, the methane emission difference and the effect of N fertilizer on methane production, oxidation and emission, the variations of methanogenic and methanotroph, and the microbiological mechanism of methane produce and oxidation were investigated using Guihuaqiu, Xudao2 and Yanjing2 as materials. The main results were as follows:（1） The methane emission from different rice cultivars had significant difference. Total methane emission during the whole growth stage, Guihuaqiu is the highest (1423 kg ha^-1), Xudao2second (1010 kg ha^-1), Yanjing2 is minimum (923 kg ha^-1). Low nitrogen fertilizer could reduce the methane emission significantly from rice paddy.（2） Different rice cultivars had significant difference in plant level. The plant dry matter, leaf area index, stem and tiller number, leaf chlorophyll content, root dry weight, root shoot ratio, root length and grain yield in Yanjing 2 and Xudao 2, were significantly higher than those in Guihuaqiu. The methane emission flux was negatively correlated with grain yield, grain number per spike and dry matter weight The correlation was not significant with the factors such as spike number, seed setting rate and thousand kernel weight（3） The rice rhizosphere soil bacteria, methanogenic and methanotroph community structure and size were studied with high-throughput sequencing and real-time PCR technology. The results showed that the microbial species difference in rhizosphere soil in different cultivars were not significant, and the proportion of dominant bacteria group was significantly different. The relative abundance of dominant methanogenic of different rhizosphere soil, methanobacterium and methanosarcina accounted for 60%-70%, and high methane emissions of Guihuaqiu rhizosphere soil in this two dominant methanogenic are higher than that of Yanjing 2 and Xudao 2. The dominant species of the methanotroph in the rhizosphere is methylosarcina and methylomonas, which is occupy 60% of the whole community. The richness of these two kinds of methanotroph in rhizosphere soil of Yanjing 2 and Xudao 2 were higher than that of Guihuaqiu. That is to say, there is a positive correlation between the abundance of methanogenic advantage group and methane emission, and the advantage methanotroph group abundance negative correlation with methane emission. The difference of bacterial communities in the soil of different cultivars were not significant The number of Yanj ing 2 rhizosphere soil of methanogenic and methanotroph were lower than that of Guihuaqiu. The number of four species of methanogenic, methanosarcina mazei, methanosarcina barkeri, methanobacterium formicium and methanobrevibacter arboriphilusare were very important for methane emission. Methane emission flux was significantly positively correlated with the size of the methane producing bacteria, and was negatively correlated with the number and activity ofthe methane oxidizing bacteria.（4） The effect of rice roots and steam ventilation system on methane emission were observed with the resin slice technique. The area of the root aerenchyma and methane release has significant negative correlation, and rhizosphere soil redox was significantly positively related, and negatively correlated with the number of methanogenic and was significantly positively related to the number of methanotroph and the activity. Stem ventilation system in the internode chamber near the ground, especially the area of gas chamber and medullary cavity had a significant effect on methane emission. the methane released greater with more area ofthe ventilation system.（5） Root to secrete substances to soil and exchange material, energy and information with soil environment, and influence the soil microbial activities, in turn, control the growth of plants. In this study, the tow molecular weight organic acids in root exudates were studied, the results showed that:the malic acid and total organic acid in root exudates were significantly positively correlated with the number of methanogenic, that is to say, malic acid promoted the activity of methanogenic archaea. The number and oxidation activity of methanotroph were significantly positive correlation with tartaric acid and citric acid, and positive correlation with lactic, and was negatively correlated with total organic acid.（6） The effect o N fertilizer on oxidation activity of methanotroph was analyzed by adding exogenous nitrogen fertilizer. The results showed that different nitrogen had double effect on the activity of methanotroph. The methanotroph activity was inhibited with the contration of 200 μg g^-1 DWS in NH₄HCO₃ and NH₄Cl and 400 μg g^-1 DWS KNO₃. The inhibition effect of Urea on methanotroph activety is slighter.