Relationship Between Methane Emission From Paddy Field And Rice Root Exudates And Soil Properties

To clarify the mechanism of the rhizosphere environment caused by the methane emission differences of different double-cropping rice varieties,three rice varieties with significant methane emission differences in early and late rice were selected as the test materials for field experiment.we collected greenhouse gas by closed static box method for field experiment,monitored the dynamics of methane emissions from different varieties of early and late rice,determinated the organic acid composition of root exudates,methanogenic bacteria,methane-oxidizing bacteria,catalase,urease activities,water-soluble organic carbon and microbial biomass carbon in rhizosphere soil of different cultivars during the main growth period.The relationship between CH₄emission and enzyme activities was analyzed by linear regression analysis.Aims to explore the different varieties of methane emission in rice growth period of methane emission characteristics,determine the influence of rice rhizosphere key characteristics of methane emissions,and build based on varieties of rice rhizosphere region features indicative of methane emission ability evaluation indexes,so as to construct rice varieties methane emissions intensity evaluation index system provides the basis.The main results were as follows:（1）The greenhouse gas and yield data showed that the cumulative CH₄emission of late rice was significantly higher than that of early rice,and Zhuliangyou 819 and Yliangyou1 with the lowest CH₄emission had the highest yield.The CH₄emission peak of different double cropping rice varieties was mainly at the tillering stage and booting stage,the highest emission peak appeared at the tillering stage,and the CH₄emission of rice was lower after milking stage.The cumulative emission of CH₄and greenhouse effect of early rice varieties were as follows:xiangzaoxian24>luliangyou996>zhuliangyou819（P<0.05）.The cumulative CH₄emission and greenhouse effect of late rice varieties were as follows:xiangwanxian17>taiyou390>Yliangyou1（P<0.05）.The CH₄emission of double cropping rice varieties was significantly different.（2）The total organic acid secretion rate of early rice cultivars was the highest in Xiangzaoxian 24,which was 259.35 ug·（g DW·h）^-1.And the lowest in Zhuliangyou819,which was 194.02 ug·（g DW·h）^-1.The secretion rate of organic acid components in the whole growth period of early rice was:tartaric acid>Acetic acid>Oxalic acid>Malic acid>Malonic acid>Citric acid>Succinic acid.The secretion rate of oxalic acid was the fastest at milking stage and the tillering rate was the fastest at tillering stage except oxalic acid.The total organic acid secretion rate of late rice varieties was the highest in Xiangwanxian 17,which was 328.45 ug·（g DW·h）^-1.And the lowest in Yliangyou 1,which was 266.73 ug·（g DW·h）^-1The secretion rate of organic acid components in the whole growth period of late rice is:Tartaric acid>Malic acid>Acetic acid>Oxalic acid>Succinic acid>Malonic acid>Citric acid.The total organic acid secretion rate of late rice was significantly higher than that of early rice.Early rice in addition to the oxalic acid,six other kinds of organic acids were very significant positive correlation with methane emissions,αup to 0.01,and late rice oxalic acid,tartaric acid,malic acid and malonic acid were very significant positive correlation with methane emissions,αup to 0.01.Acetic acid,citric acid,succinic acid and methane emissions,（P>0.05）.There is no obvious correlation between early rice varieties organic components and the correlation between methane emissions than late rice varieties.（3）There was a significant negative correlation between methane-oxidizing bacteria and methane emission in double cropping rice（P<0.01）,and there was no significant correlation between methanogens and methane emission（P>0.05）.The number of methanogens in different varieties of early rice showed basically the same changing trend,which increased first,then decreased,and then increased again.The methanogens increased first and then decreased,and the differences among different varieties were obvious.The number of methanogens was the lowest in Zhuliangyou 819,and the number of methanogens was the highest in Zhuliangyou 819.There was no obvious consistent change rule of methanogenic bacteria in late rice varieties,but the number of methanogenic bacteria showed a gradually increasing trend.There was no significant difference in the number of methanogenic bacteria among varieties at maturity stage.The number of methanogenic bacteria in Yliangyou 1 was the lowest,and the number of methanogenic bacteria was the highest.（4）The activities of catalase and urease in rhizosphere soil of double cropping rice varieties were different at different growth stages,the catalase activities of early rice were the highest at booting stage,and those of late rice were the highest at tillering stage.The cumulative methane emissions of late rice varieties were significantly higher than that of early rice.Catalase activities of early rice were highest at booting stage,catalase activities of late rice and urease activities of early and late rice rice were highest at tillering stage.The activity of catalase and urease in rhizosphere soil of different early and late rice varieties were different at different growth stages.The positive correlation between methane emission and urease in double-cropping rice field reached an extremely significant level（P<0.01）,and the positive correlation with catalase reached a significant level（P<0.05）.In conclusion,methane emission of rice varieties was closely related to catalase and urease in rhizosphere soil of rice,reduced the activity of catalase and urease in soil was beneficial to reducing methane emission in rice field.（5）The CH₄emission flux of rice cultivars had a positive linear correlation,but had no significant correlation with the WSOC of double cropping rice cultivars.The content of WSOC in the rhizosphere of the three early rice cultivars was the highest at booting stage,ranging from 619.7-714.93 mg·kg^-1,while that of the late rice cultivars was the highest at full heading stage,ranging from 1112.18-1472.9 mg·kg^-1.The microbial biomass carbon content of Xiangzaoxian 24 and Zhuliangyou 819 increased first and then decreased during the whole growth period,and the microbial biomass carbon content was the highest at booting stage.Luliangyou 996 had slight differences,showing a trend of increasing first,then decreasing,and then increasing at milking stage.The microbial biomass carbon content of late rice Yliangyou 1 first decreased with the increase of time,and increased at milking stage.The urease activity of Taiyou 390 and Xiangwanxian 17 had the same variation trend at different stages,which basically decreased first and then increased,and finally decreased at milking stage.（6）The secretion rate of tartaric acid,malic acid and malonic acid,the activities of catalase and urease,the absolute quantity of methane-oxidizing bacteria（pmo A gene）and the content of microbial biomass carbon can be used as indicators to evaluate the methane emission capacity of rice plants.