Effects Of Nitrogen Fertilizer Application And Rice-crab Co-culture System On Paddy Soil Microbiology In Liaohe Delta

The Liaohe Delta region is one of the main rice production bases in northeast China.Large amounts of nitrogen fertilizer was used to ensure grain security,while the rice-crab co-culture system has been widely expended in this aera.Nitrogen fertilizer application and crab rising may affect the soil environment,thus microorganisms may be changed.Based on the long-term location experiment of Liaoning Academy of Agricultural Sciences,the effects of nitrogen fertilizer application and rice-crab co-culture system on microorganisms in paddy soil was studied.The results are presented as follows:1.When increasing the nitrogen fertilizer,soil pH?total C content and C:N increased,while organic matters,A-P and NH₄⁺-N content decreased,the content of organic matter and A-P decreased by 28.63%and 42.59%under N420 treatment;total N and NO₃^--N content first decreased and then increased.The maximum value was reached under N420 treatment.Fertilization increased phosphatase activity and sucrase activity in paddy soil,the phosphatase activity increased significantly,with an increase of 14.71%;the urease activity decreased;the catalase activity firstly increased and then decreased,N420 treatment is lower than N260 treatment.2.The composition and structure of bacterial and fungal communities in the soil changed obviously under the effect of fertilization.Both bacteria and fungi species richness increased when increasing nitrogen content,the diversity of bacterial and fungal communities in N420 treatment increased by 4.98%and 38.92%compared with N0 treatment.After fertilization,the relative abundance of Proteobacteria and unclassified first increased and then decreased.The relative abundance of Chloroflexi and Acidobacteria decreased gradually,while Actinobacteria and Bacteroidetes became the dominant phylum after fertilization.It increases the total carbon content in the soil and promotes the material cycle in the soil.After fertilization,the relative abundance of Ascomycota first increased and then decreased.The relative abundance of Basidiomycota gradually increased.It is beneficial to improve the ventilation of soil;the relative abundance of Unclassified fungi first decreased and then increased.After fertilization,Zygomycota and Chytridiomycota are no longer the dominant phylum.The analysis of ecological network showed that the structure of total microbial ecological network had the best stability in N260 treatment,and the crop yield was the biggest in this treatment,so N260 treatment was the best nitrogen fertilizer.Organic matter is the main environmental factor that causes the change of bacterial and fungal community composition.3.Soil pH,organic matters,total N,NH₄⁺-N content increased,while C/N decreased significantly in rice-crab system.The soil enzyme activities decreased in rice-crab system,the decreases were 40%and 20%respectively.While urease and phosphatase activities decreased significantly.4.In addition,both bacteria and fungi species richness increased in rice-crab system.The diversity of bacterial communities increased,however the diversity of fungal communities decreased.The bacterial diversity increased,while the fungal diversity decreased.The relative abundance of Proteobacteria and Acidobacteria decreased,Proteobacteria decreased by 46.72%.while Chloroflexi,Actinobacteria and Bacteroidetes increased,and increased by 63.26%,64.55%and 48.72%.It is conducive to the decomposition of organic matter and promote the circulation of nutrients.The relative abundance of Ascomycota increased,and increased by 65.53%.While Basidiomycota decreased.Reduce the occurrence of plant diseases.The analysis of ecological network showed that the structure of total microbial ecological network had the best stability and the crop yield was the biggest in this treatment.Soil phosphatase activity is the main factor that affects the composition of soil bacterial community,and TN is the main factor that affects the change of soil fungal community.The composition and structure of soil bacterial community changed obviously under rice-crab co-culture system.