| Improving the efficiency of nutrient absorption and utilization,especially the nitrogen fertilizer in rice,and increasing the biomass have been the hot topics for breeding scientists to improve the yield of rice.In addition,it is also a common method to increase the yield of rice by increasing the application of nitrogen fertilizer.However,the continuous increase of nitrogen fertilizer application,on the one hand,it will lead to soil compaction and acidification,on the other hand,it will cause resource waste and environmental pollution,and induce greenhouse gas emissions.To improve the efficiency of nitrogen absorption and utilization of rice and broaden the transfer channels of nutrients from source to storage not only can guarantee the safety of food production,but also reduce greenhouse gas emissions and bring environmental benefits,which responds to the national policy call of green agriculture.Therefore,it is of great significance to study the effect of nitrogen efficient rice on greenhouse gas emissions in paddy fields.Previous studies of our laboratory,already found the preliminarily molecular mechanism of OsNAR2.1 in affecting the absorption and utilization of nitrogen fertilizer,and the overexpression material pOsNAR2.1:OsNAR2.1 has been created,which has confirmed the phenotypic characteristics of its high efficient absorption and utilization of nitrate.This study will combine the previous research results to explore the characteristics of the influence of overexpression of OsNAR2.1 gene in rice on greenhouse gas emissions in the field.In addition,according to relevant literature reports,greenhouse gas emissions are closely related to microorganisms,aerenchyma and other factors.Therefore,we studied the effects of rice overexpression of OsNAR2.1 gene on rhizosphere soil-related functional microorganisms,root aerenchyma and soil physical and chemical properties,and elucidated the role mechanism of pOsNAR2.1:OsNAR2.1 overexpression material affecting greenhouse gas emissions in rice fields.In addition,we also introduced the rice mutant line osnar2.1,with OsNAR2.1 gene knockout to further clarify the relationship between overexpression and mutant lines affecting greenhouse gas emissions and related factors.In summary,the main research results are as follows:Research for three consecutive years showed that,in the field growth condition,compared with the wild type,the methane emission flux and total cumulative seasonal emission volume were reduced,and reached a significant level under the low-nitrogen controlled water treatment in pOsNAR2.1:OsNAR2.1 overexpression line.Compared with the wild type,the cumulative methane emissions of overexpression line were reduced by 70.6%,40.0%,41.1%,and 22.0%,respectively,under the four treatments of low nitrogen controlled water,low nitrogen flooded,high nitrogen controlled water,and high nitrogen flooded.Compared with the wild type,the methane emission flux and total seasonal cumulative emission of OsNAR2.1 gene mutant materials increased,which was significant under medium nitrogen controlled water treatment.Compared with the wild type,the cumulative methane emissions of the mutants increased by 25.2%and 21.6%,respectively,under medium nitrogen controlled water and medium nitrogen flooded treatment.Compared with the wild type,The carbon dioxide emission flux of the overexpression line was not significantly different from wild type,and the total cumulative emissions of the overexpressed material were significantly increased under controlled water treatment,but the difference was not significant under flooded treatment.Compared with the wild type,the cumulative carbon dioxide emissions of overexpression line increased by 17.5%,4.6%,19.0%,and 36.2%,respectively,under the four treatments.There was no significant difference in the carbon dioxide emission flux between the mutant material and the wild type.But cumulative emissions decreased significantly.Compared to the wild type,the cumulative carbon dioxide emissions of the mutants were reduced by 19.5%and 10.8%,respectively,under the two treatments.Compared with the wild type,the emission flux of nitrous oxide has not significantly different in overexpression line.Compared with the wild type,the total nitrous oxide emissions of the overexpressed material decreased by 59.1%under the low nitrogen controlled water treatment,increased by 222.8%under the low nitrogen flooded treatment,increased by 27.6%under the high nitrogen controlled water treatment,and decreased by 3.9%under the high nitrogen flooded treatment.Furthermore,compared with the wild type,the total cumulative emission of nitrous oxide of mutant was significantly reduced under controlled water treatment and significantly increased under flooded water treatment.Compared with the wild type,the nitrous oxide emission of the mutants was reduced by 41.0%under the medium nitrogen controlled water treatment,and increased by 207.0%under the medium nitrogen flooded treatment.In conclude,by the results of experiments of the overexpression and mutant material which are showed opposite results to the wild type.Overexpression and knockout of OsNAR2.1 gene in rice material can significantly influence the emission of greenhouse gases,as demonstrated.In the field,the observation of root aerenchyma of overexpressed material and wild type material showed that the aerenchyma development of the overexpression material lagged behind wild type,and the aerenchyma formation area was significantly lower than wild type.The aerenchyma of mutant material was formed earlier than wild type,and the aerenchyma area was significantly higher than wild type.Therefore,it is concluded that overexpression and knockout of OsNAR2.1 gene in rice material can affect the development of aerenchyma and may affect the transportation of greenhouse gases,especially methane,to affect the emission of greenhouse gases.The results of correlation analysis between the greenhouse gas flux and the influencing factors of overexpressed line are as follows:methane emission flux is mainly positively correlated with AK、WC、NH4+-N、TN、mcrA、archaeal-amoA、bacteria-amoA and nirS,while negatively correlated with pmoA and nirK.The emission flux of nitrous oxide was positively correlated with WC、NO3--N、nirS and nosZ,but negatively correlated with bacteria-amoA.Carbon dioxide emissions had positive correlation with AP、NO3--N、mcrA、pmoA and nirK,but negative correlation with pH、AK、WC、TOC and nosZ.The results of soil-related functional microorganisms in greenhouse gas emissions from rice fields showed that,compared with wild type,the abundance of methanogens in the rhizosphere of the overexpressed material was significantly reduced,while the abundance of methanogens was significantly increased.Also,the abundance of methanogens in the rhizosphere of the mutant material was significantly increased,and that of methanogens was significantly decreased.It is concluded that overexpression and knockout of OsNAR2.1 gene in rice material can regulate methane emission by affecting the abundance of rhizosphere microorganisms.In summary,our results indicate that overexpression or knockout of OsNAR2.1 gene can regulate greenhouse gas emissions,especially methane,by influencing the number of rhizosphere functional microorganisms,especially the abundance of mcrA and pmoA,and the development of root aerenchyma,thus providing a theoretical basis for the development of green and high-yield rice. |
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