Effects Of Rice-Fish Co-Culture On Soil Micro-Habitats And Fish Internal Environment And Their Interactions

Rice-fish co-culture is one of the "globally important agricultural heritage systems" and has a history of more than 2,000 years in Asia.Rice-fish co-culture has a history of more than1,600 years in China,mainly concentrated in central,southwest,east,south China.The mountainous area is an excellent area for the development of rice-fish co-culture due to its abundant water resources and rich rice planting techniques in the north of Guangdong Province.Meanwhile,rice-fish co-culture is the main way for local farmers to get rid of poverty.At present,there are few reports on the relationship between soil microorganism at different levels and the intestinal environment of breeding objects in rice-fish co-culture.In this study,the rice-fish co-culture group(RF)and rice monoculture group(RM)were set to sample the soil at different levels(0-2cm,2-4cm,4-6cm,6-8cm,8-10 cm,10-15 cm and 15-20cm)in different culture periods(early and late periods),and to conduct systematic analysis in time and space.The soil environmental factors of the two paddy systems were measured and analyzed by means of ecological research.High-throughput sequencing technology was used to identify and analyze the species and abundance of microorganisms in soil and fish gut of the two groups.Then,the stability of soil microorganism system of the two models was analyzed by using ecological network.The differences in serum biochemical indexes and intestinal tissue structure between rice-fish co-culture system and pond cultured carp were studied by biochemical analysis,aiming to explore and analyze the differences in the health status of fish affected by the same species of paddy field culture and pond cultured carp.Finally,the interaction between soil environmental factors and microbial community structure and fish internal environment in the rice-fish co-culture system was comprehensively analyzed,and the main results were as follows:(1)Effects of rice-fish co-culture on soil physicochemical factors and enzyme activities.The results showed that,the rice-fish co-culture significantly increased the soil p H,total phosphorus and available phosphorus contents in the early stage,and the contents of ammonia nitrogen,available phosphorus,available potassium and microbial biomass phosphorus in the later stage(P < 0.05).In terms of different layers,soil nutrient contents in RF group and RM group showed the same trend with stratification.Soil nutrient contents,microbial biomass and enzyme activities in RF group were gradually decreased with soil depth deepening.Compared with 0-10 cm,soil nutrient contents in 10-20 cm were significantly decreased(P < 0.05).Among them,available potassium content gradually accumulated at 10-20 cm in the later stage of ricefish co-culture.(2)Effects of rice-fish co-culture on soil microbial community structure.The experimental results show that the soil door level and the level of bacterial community structure,rice-fish coculture unchanged 0-20 cm of soil microbial species composition,but Proteobacteria,Acidobacteria,Chloroflexi,Firmicutes and dominant fungi of the genus obvious changes have taken place in the relative abundance.RDA results showed that at the soil level of 0-2 cm,the contents of nitrate and total phosphorus during the whole period of rice-fish co-culture significantly affected the change of bacterial community structure.At 2-10 cm,p H had a great effect on the bacterial community structure.At 10-20 cm,p H and ammonia nitrogen were the main physicochemical factors affecting the bacterial community structure.In the late planting period,the soil bacterial communities of 0-10 cm and 10-20 cm in RF group concentrated in the areas with higher total nitrogen content and organic carbon content,respectively.The ecological network results showed that the interaction between bacteria and microorganisms in the RF group was more positive(89.89% and 79.58%)than that in the RM group(80.00% and 78.78%)before and after the rice-fish co-culture.(3)Effects of paddy environment on serum biochemical indexes,intestinal tissue morphology and bacterial community structure of cultured carp.The results showed that compared with pond culture under the same conditions,paddy field environment significantly improved the growth performance of carp.The contents of AST,ALT and MDA in serum were decreased,and the contents of complement C3 and C4 were increased.The length of intestinal microvilli in rice-fish co-culture group was shorter,which was not conducive to the absorption of nutrients.Compared with the pond-farmed fish control group,the intestinal microbial diversity of rice-fish co-culture group was increased.Significant differences were found in the abundance of Fusobacteria,Verrucomicrobia,Proteobacteria,Alphaproteobacteria,Actinomycesbovis,Cetobacterium,Aeromonas,Plesiomonas and Bacteroides.(4)Interaction analysis of soil physical and chemical factors and microbial community structure with fish internal environment.The results showed that in the rice-fish co-culture mode,the similarity between the intestinal bacteria species and the soil 0-10 cm and 10-20 cm bacteria species was 30.52% and 29.16%,respectively.Spearman correlation analysis showed that 8genera were significantly correlated(P < 0.05),8 genera were significantly correlated(P <0.01),and there was no significant correlation at the 10-20 cm level(P >0.05).Spearman correlation analysis of intestinal microorganism and soil physical and chemical factors 0-10 cm showed that there were 4 bacterial genera significantly correlated with physical and chemical factors in soil(P < 0.05),4 bacterial genera significantly correlated with physical and chemical factors in soil(P < 0.01),and there was no significant correlation at 10-20 cm level(P > 0.05).The results showed that compared with rice monoculture,rice-fish co-culture improved the transformation of nutrients in soil and provided abundant nutrients for rice growth.In addition,the diversity and complexity of microbial community structure in soil and intestines of carp were improved to ensure the growth requirements of rice and carp.At the same time,the rice-fish co-culture changed the physicochemical factors and microbial species abundance at some soil levels,but did not change the composition of dominant species.The species composition of intestinal bacteria of carp was closer to that of soil 0-10 cm,and the correlation was greater.Therefore,rice-fish co-culture mode can improve soil fertility and internal environment stability,and enhance the stability and health of the intestinal environment of carp,which is worthy of promotion.