Effects Of Rice-Fish Symbiosis Years On Topsoil Nutrients And Microorganism

In recent years,rice-fish co-culture system has attracted extensive attention from society and academic circle because of the economic benefits of "combination of planting and breeding,double harvest in one field" and ecological advantages of "fertilizer and herbicide free".In order to explore the change of paddy soil environment under long-term rice-fish symbiosis system and the impact of application years,this study analyzed the paddy soil under the rice-fish symbiosis system for 2 years(RT2),5 years(RT5)and 8 years(RT8).We measured soil chemical properties(including total nitrogen,alkali-hydrolytic nitrogen,total phosphorus,available phosphorus,total potassium,available potassium,organic matter and p H),and soil enzyme activities(including urease,sucrase and catalase).16 Sr DNA sequencing analysis of soil bacteria were carried out by using high-throughput sequencing technology to compare the soil environment of rice-fish symbiotic fields at different years.The results are as follows:1.The contents of soil total N,alkali-hydrolytic N,total P and available P in RT8 were significantly higher than those in RT2,while the contents of soil total K,available K and organic matter were lower than those in RT2,and the difference of organic matter was significant.The soil available P and total P in RT5 were significantly higher than those in RT2,while the contents of alkali-hydrolysed N and organic matter in RT5 were significantly lower than those in RT2.2.The activities of urease,sucrase and catalase in RT8 were significantly higher than those in RT2,the activities of sucrase and catalase in RT5 were significantly higher than those in RT2,and the activities of urease were significantly lower than those in RT2.3.Correlation analysis showed that there was a significant positive correlation between soil sucrase and total P and total N.Urease was positively correlated with available K and alkali-hydrolyzable N,and was positively correlated with total potassium and total nitrogen.Catalase has a significant positive correlation with available phosphorus.4.16 Sr DNA sequencing result divided the bacterial community into 51 phyla,136 classes,192 orders,337 families,557 genera and 113 species.The diversity of soil bacterial community was RT5>RT8>RT2.From phylum to family,RT8 showed more significant difference in bacterial taxa(i.e.,more key species affecting bacterial community structure),followed by RT5 and RT2.5.Correlation analysis between community diversity and soil chemical properties showed that there was a significant negative correlation between soil total K and available K and bacterial community diversity,while a significant positive correlation between available P and community diversity.6.Correlation analysis of soil bacterial community structure and chemical properties showed that total P in RT2 was negatively correlated with Tectomicrobia,Latescibacteria and Thaumarchaeota.Total K and available P in RT5 were significantly positively correlated with Tectomicrobia,Firmicutes,Actinobacteria and Elusimicrobia,and negatively correlated with Acidobacteria,Latescibacteria and Cyanobacteria.In RT8,available P were the maximal factor which related to the relative abundance of bacteria phylum,followed by alkali-hydrolytic N and p H.The content of soil available P was significantly negatively correlated with RT8 specific bacteria Cloacimonetes and Tenericutes.Deinococcus-thermus,Tenericutes,Planctomycetes and Verrucomicrobia showed extremely significant negative correlation with alkali-hydrolytic nitrogen,and extremely significant positive correlation with p H.7.Correlation analysis of bacterial community structure and soil enzymes showed that urease was the maximal factor affecting the relative abundance of soil bacteria,which was significantly positively correlated with Proteobacteria,Bacteroidetes,Deinococcy-Thermus and Firmicutes,and significantly negatively correlated with Acidobacteria.8.The actual rice yield of RT2,RT5 and RT8 and its yield components showed that the actual rice yield of RT2,RT5 and RT8 was significantly different,which was shown as RT8<RT5<RT2.The 1000-grain weight and effective panicle number of RT8 were significantly lower than those of RT2.With the increase of the application years of rice-fish symbiosis system,the soil phosphorus content(available P,total P)and soil nitrogen content(alkali-hydrolytic N,total N)increased,the soil potassium content(available K,total K)decreased,and the activities of urease,sucrase and catalase enhanced.The key strains affecting the bacterial community structure in the paddy soil significantly increased,the soil bacterial community diversity showed a trend of increasing at first and then decreasing,and the rice yield decreased with the increase of application years of rice-fish symbiotic system.