Study On The Differences In Root And Rhizosphere Soil Properties Of Double Seasonal Rice Varieties With Different Methane Emissions

Methane is an important greenhouse gas,and rice paddy is one of the main sources of methane.It is important to study the formation mechanism of methane emission differences among rice varieties.In this study,three varieties of early and late rice with high,medium and low methane emission were used as the target.Through the field experiment,the root-shoot ratio,root volume,root porosity and root activity of different rice varieties were observed.The activities of sucrase,urease and methanogens in rhizosphere soil of rice were studied.The differences in root and rhizosphere soil characteristics between rice varieties were compared,and the main factors affecting methane emissions from different rice varieties were analyzed.The main findings are as follows:（1）Methane emission fluxes in early and late rice showed consistent changes in seasonal variation,The highest emission flux during the tillering period.As the rice grows,the methane emission flux gradually decreases,and there is almost no methane emission in the late growth stage（milk ripening stage）.Among them,the methane emission fluxes of three early rice varieties were in the order of Xiangzaoxian 24,Luliangyou 996,and Zhuliangyou 819.The average methane emission flux of Xiangzaoxian 24 at the tillering stage was significantly larger than that of Luliangyou 996 and Zhuliangyou 819,with differences of 36.23%and 23.46%,respectively.The methane emission fluxes of three late rice varieties were in the order of Xiangwanxian 17,Taiyou 390,and Y Liangyou 1.The average methane emission flux of Xiangwanxian 17 was significantly higher than that of Taiyou 390 and Y Liangyou 1 at the tillering stage,with differences of 55%and 54.95%,respectively.In the filling stage,Xiangwanxian 17 was significantly larger than Y Liangyou1,but there was no significant difference between Taiyou 390 and Y Liangyou 1.（2）The results of the comparison of root characteristics of early rice are,the root-shoot ratio of Xiangzaoxian 24 in Full heading period was significantly higher than that of Luliangyou 996 and Zhuliangyou 819.There was no significant difference in root volume between the three varieties.Significant differences in root porosity.The root injury flow of Luliangyou 996 was significantly greater than that of Xiangzaoxian 24 in the milk ripening period.The root-shoot ratio of Y Liangyou 1 in the late rice was significantly greater than that of Xiangwanxian 17 at the heading stage,Taiyou 390 in milk ripening period is significantly larger than Y Liangyou 1.The root volume of Y Liangyou 1 at the heading stage was significantly larger than that of Xiangwanxian 17 with a range of 19.68 ml·strain^-1.Root porosity ranges from 0.142 to 0.364,there are significant differences among the three varieties in each period.The root injury flow rate of Taiyou 390 in the tillering period was significantly greater than that of Xiangwanxian 17 and Y Liangyou 1.（3）The invertase activity of early rice was expressed in the milk ripening stage,Luliangyou 996 was significantly larger than Zhuliangyou 819,and the urease activity of Xiangzaoxian 24 at the heading stage was significantly greater than that of Zhuliangyou 819.The invertase activity and urease activity of late rice were the highest in the late tillering stage and the milky stage.The number of methanogens in the rhizosphere soil was the highest in the early rice Xiangzaoxian 24（in the peak period）.The number of methanogens in late rice at the peak of tillering was Taiyou 390>Xiangwanxian 17>Y Liangyou 1.（4）The main factors affecting early rice methane emission are root-shoot ratio.Late rice is root-shoot ratio and root porosity,which are significantly positively correlated with methane emission flux.There is a positive correlation between the methane emission flux of early rice varieties and the number of methanogens in rhizosphere soil;There was a significant positive correlation between the methane emission fluxes of late rice Taiyou 390and Xiangjingjing 17 and the number of methanogens in rhizosphere soil（p<0.05）.There was a negative correlation between Y Liangyou 1 and the number of methanogens in rhizosphere soil,but it was not significant.Therefore,among the tested varieties in this test,reducing the root-shoot ratio of early rice varieties and root-shoot ratio and root porosity of late rice can reduce methane emissions;reducing the activity of invertase in rhizosphere soil and reducing the number of methanogens in rhizosphere soil can also reduce methane emissions.