Effects Of Nitrogen-fixing Cyanobacteria And Promoting-decomposing Agent On On Rice Soil Microorganisms, Yield And Quality

A lot of rice straws were produced in China every year.Unreasonable use of Straw would cause environmental pollutionand waste of resources.Excessive carbon nitrogen ratio(C/N)of straw affect the function of microorganisms decomposing straw.Chemical nitrogen fertilizer is required to adjust the C/N of the decomposed substrate and promote the decomposition of rice straw.Nitrogen-fixing cyanobacteria are photosynthetic autotrophic organisms with nitrogen-fixing ability.It can supply nitrogen for a long time in paddy fields.If nitrogen-fixing cyanobacteria can be used instead of chemical nitrogen fertilizers,it is of great significance in agricultural production.In this study,a nitrogen-fixing cyanobacterial complex system was constructed using restricted culture techniques.The community composition of the nitrogen-fixing cyanobacteria complex system was detected using high-throughput sequencing technology.The ability of 6 commercially available straw promoting-decomposing agent to degrade rice straw combined with nitrogen-fixing cyaobacterial complex system was evaluated.Nitrogen-fixing cyanobacteria and microbial promoting-decomposing agent were applied to potted rice at regular dosages,and the effects of nitrogen-fixing cyanobacteria and promoting-decomposing agent on rice yield and quality were explored.Changes in soil bacterial community,soil enzyme activity,and microbial counts were detected.The purpose of this study was to clarify the effects of nitrogen-fixing cyanobacteria and promoting-decomposing agent on bacterial communities in high-yield and high-quality rice soils.The following research results were as follows:1.After mixing water samples and soil samples from multiple sites,the nitrogen-fixing cyanobacteria flora was richened in a nitrogen-free BG-11 liquid medium.DNA of nitrogen-fixing cyanobacteria complex system was extracted,and high-throughput sequencing was performed based on 16 S rRNA and nifH genes to analyze community composition.There are three main types of cyanobacteria with high abundance in this system: Limnothrix,Leptolyngbya,and Calothrix.Some associated bacteria with cyanobacteria and some nitrogen-fixing bacteria were also detected.2.Using the plate culture method,14 groups of treatments were set up,and the combination of 6 kinds of microbial promoting-decomposing agent and nitrogen-fixing cyanobacteria to degrade rice straw was selected.The results found that all 6 promoting-decomposing agent could promote the decomposition of rice straw.At the end of the cultivation,the straw weight loss rate of QF+L was as high as 30.09%.In the course of plate culture,Yu Qifu is a good promoting-decomposing agent,and the addition of nitrogen-fixing cyanobacteria can promote the degradation of rice straw.3.Under the background of 30% straw return to the field,4 treatments are set up,namely,only the straw return to the field(CK),straw + promoting-decomposing agent(SDS-),straw + nitrogen-fixing cyanobacteria(CS-),and straw + nitrogen-fixing cyanobacteria + promoting-decomposing agent(SDCS-),each treatment was repeated 5 times.The test results found that SDS-increases the chalkiness of rice,reduces the appearance quality of rice.The abundance of stress-resistant bacteria(Methylocystis)and participated in the carbon cycle bacteria(Candidatus_Brocadia)were decreased.Soil urease activity at booting stage was significantly reduced.CS-treatment reduces chalkiness,improves appearance quality of rice.The abundance of biocontrol bacteria(Lysobacter)and microcystin-degrading bacteria(Sphingopyxis)increased in postulation stage.Urease increased significantly during booting and maturity stages.SDCS treatment reduces chalkiness and improves the appearance quality of rice.The abundance of cellulose-degrading bacteria(Cytophaga)and bacteria(Syntrophorhabdus)involved in circulation of materials were increased.Soil urease and invertase activities increased during booting and maturity stages.Based on the analysis of community structure,it was found that the soil bacterial community in SDS,CS and SDCS changed significantly compared with those of the control.4.Under the background of full-volume return to the field,there are 6 treatments,that is,straw return to field(CK),straw + promoting-decomposing agent(SDS),straw + nitrogen-fixing cyanobacteria(CS),and straw + nitrogen-fixing cyanobacteria + promoting-decomposing agent(SDCS),reducing fertilizers by 20%+ straw + promoting-decomposing agent(SDDS),reducing fertilizaters by 20% + straw + nitrogen-fixing cyanobacteria + promoting-decomposing agent(SDCDS),repeated 9 times.The results found that SDS could significantly increase the theoretical yield of rice by 20.38% and reduce the quality of rice under normal fertilization,.Soil samples were subjected to high-throughput sequencing based on 16 S rRNA and nifH genes,and it was found that the promoting-decomposing agent could increase the abundance of Anaerolineaceae that can promote plant growth,Anaerolinea that can promote the decomposition of organic carbon in rice soil,and that of Acidobacteriales that can degrade dead wood.The abundance of some beneficial bacteria in the soil were reduced,such as Geobacter participating in the arsenic cycle,Leptolinea measuring indicators of pesticide residues,and Desulfobulbus that can inhibit methane production in the soil.Soil catalase,invertase and phosphatase activities were significantly increased.CS,SDCS and SCDDS treatments can reduce the chalkiness,improve the appearance quality of rice.The abundance of Azoarcus with nitrogen-fixing ability from nitrogen-fixing cyanobacteria line increased,and the abundance of Algoriphagus,Hoeflea and Pseudodesulfovibrio decreased significantly.SDCDS treatment can reduce the chalkiness and improve the quality under the condition of reducing fertilization by 20%.It can also ensure that the yield of rice is not reduced.The relative abundance of Anaerolineaceae and UTCFX1 in SDCDS treatmentare significantly increased.SDCS and SDCDS treatments can increase soil urease and phosphatase activities.From the analysis of community structure,it was found that the soil bacterial community structure of the treatment group changed based on sequencing results of the 16 SrRNA gene.The soil bacterial community applied with nitrogen-fixing cyanobacteria changed greatly based on sequencing results of nifH gene,and other treatments had little effect on the community structure.In summary,when the full amount of straw is returned to the field and conventional fertilization,tested promoting-decomposing agent can increase the yield and reduce the appearance quality of rice.Nitrogen-fixing cyanobacteria have the ability to improve the quality of rice.Under the condition of fertilizers reduced by 20%,both nitrogen-fixing cyanobacteria and promoting-decomposing agent can ensure that rice does not reduce yield,and alter the growth of rice by affecting the community composition of bacteria in the soil.Some nitrogen-fixing bacteria from the nitrogen-fixing cyanobacteria system have increased their abundances under the application of nitrogen-fixing cyanobacteria.The large-scale application of the two needs further experiments to be promoted.