Study On The Ecological Diversity Of Cyanobacteria In Rice Fields And The Nitrogen-fixing Cyanobacteria Promotion Effect On Rice

Nitrogen-fixing cyanobacteria are a microbial resource with important agricultural value,but there are obvious regional differences in cyanobacteria community composition,structure and diversity.It is of great practical importance to clarify the distribution of soil cyanobacteria in different ecological regions and to search for efficient nitrogen-fixing cyanobacteria strains for the development and application of indigenous nitrogen-fixing cyanobacteria resources.At present,there is still a gap in the research on the composition,structure and diversity of soil cyanobacteria communities in the wetlands of Jilin Province,which is located in the inland climate of Northeast Asia.Therefore,in this study,the composition,structure,diversity and environmental drivers of soil cyanobacteria communities in paddy fields from six different regions of Jilin Province were investigated using 16S sequencing technology combined with morphological observations.The soil nitrogen-fixing cyanobacteria from each region were also isolated and identified.In this study,a total of five nitrogen-fixing cyanobacteria were isolated and purified from paddy soils in Jilin Province,and the effects of nitrogen-fixing cyanobacteria on rice seedling growth,soil fertility and soil microbial community were investigated by pot experiments under the premise of elucidating their growth and nitrogen-fixing characteristics.The main research results were as follows:1.16S r DNA high-throughput sequencing detected a total of 16 classes,33 orders,60families and 113 genera of cyanobacteria in Jilin paddy soils.Among them,Cyanobium＿PCC-6307 and Nodosilinea＿PCC-7104 were the dominant cyanobacteria populations in the soil of rice fields in Jilin Province.Microscopic examination revealed the presence of a considerable proportion of filamentous cyanobacteria Planktothrix,Anabaena,Leptolyngbya and Nostoc in each soil sample.2.The cyanobacteria community composition,structure and diversity showed regional differences.Alkaline soils S1,S2 and S5 had higher diversity than acidic soils S3,S4 and S6,with S5 having the highest cyanobacteria diversity.PCo A（Principal Co-ordinates Analysis）analysis showed that soil cyanobacteria communities in different regions were clustered and showed regional differences in distribution.The effects of p H and organic carbon（SOC）on cyanobacteria communities were most significant.The correlation coefficients for the effects on cyanobacteria communities were 0.8948 and 0.8370,respectively.3.Five silk-shaped fixing nitrogen-fixed-nitrogen cyanobacteria GD2,GD8,GD9 and GD10 are separated from the paddy field soil.Through research on the growth characteristics of algae,the growth rate and growth status of GD2 are significantly better than other algae plants.GD2 biomass weight accumulation and chlorophyll content is high,reaching 0.48 mg·L^-1,11.79mg·L^-1,respectively.The content of carbon nitrogen is also significantly higher than other algae plants,which are 27.71%and 1.75%,respectively.At the same time,GD2 and GD8 have a good phosphorus-dissolving ability,and the maximum phosphorus dissolved amount reaches 46.27mg·L^-1,39.65 mg·L^-1.4.Algae plant GD2 and GD8 have the highest nitrogen enzymes,with 68.23 U·mg^-1and40.12 U·mg^-1,respectively.The changes in temperature,p H,and light will affect the nitrogen enzyme activity of each algae.Between 22℃and 30℃,the algae plant fixing enzyme activity increased with the temperature rising.Between p H=5-10,algae solid azonase activation shows the trend of increased first and then decrease with the increase of the p H value.Each algae has the largest nitrogen enzyme activity between p H=7-8,which are 72.22 U·mg^-1,21.18 U·mg^-1,42.08 U·mg^-1,9.3 U·mg^-1,7.56U·mg^-1.The changes in light darkness have a greater impact on the nitrogen enzyme activity of GD2,and the response of the remaining algae plant fixing enzymes has less response to the change of light darkness.GD2’s nitrogen enzyme activity under dark conditions is significantly higher than light conditions.Given that GD2 and GD8have good growth characteristics and nitrogen fixation ability,the results of molecular identification of the two algae plants indicate that the GD2 is Nostoc sp.,GD8 is Anabaena sp..5.Applying nitrogen-fixed-nitrogen algae can improve the growth of rice.After applying nitrogen-fixed-nitrogen algae,the content of rice root,plant height,SPAD and rice blades,soluble proteins,ammonia nitrogen,and nitrate nitrogen content have improved to varying degrees.Among them,the height of rice plants after GD2 and SPAD is the largest.Except for GD10,other algae plants can significantly increase the roots of rice.The content of the soluble protein and the total nitrogen content of rice leaves after GD2 is the highest,the ammonia nitrogen content treated with GD8 is the highest,and the nitrogen nitrogen content treated with GD10 is the highest.Treatment of nitrogen algae can increase the activity of rice blades NR,GS,and GOGAT.The GD2 processing of rice blades NR and GS still show the highest activity,which increased by 498.64%and 56.22%,respectively.GD3 has the largest GOGAT activity.In summary,it is found that the promotion of GD2 and GD8 pairs is better.6.The number of soil bacteria after applying nitrogen-fixed-nitrogen has increased by133%-366%.In addition to nitrogen fixation and phosphorus bacteria,the number of other functional microorganisms has increased significantly,and the number of soil microorganisms in the root is increasing.The PLFAS analysis also results in the same results.The total PLFAS content in the root soil increases,but the GD8 and GD10 will reduce the content of Gram-negative bacteria and Gram-positive bacteria PLFAS.Nitrogen-fixed-nitrogen algae will enhance the use of carbon sources soil microorganisms.In addition,after applying nitrogen-fixed-nitrogen algae,it can also increase the content of soil nitrogen and increase the activity of soil enzymes,sugarase,phosphatase,and peroxide enzymes.