Study Of Water Physi-Chemical Factors,Zooplankton And Water Microbial Community Structure Of Rice-Crayfish Integrated System

Rice-crayfish integrated system（RC）is an ecological faming system which makes full use of the advantages of rice fields and water resources in the plain area for rice（Oryza sativa）planting and crayfish（Procambarus clarkii）culturing.Rice and crayfish mutual benefit each other in the integrated system with higher ecological,economic and social benefits,and has been promoted in Hubei,Jiangsu and other areas.However,the basic ecological research and the theoretical foundation of RC is still lacking.Thus,farmers often apply lots of chemical fertilizers and feeds during the production process,resulting wastes of resources and restricting the sustainable development of RC.As one of the most important components of the ecosystem,the water environment directly affects the production capacity,animal/plant health,and the ecological environment quality of the agroecosystem.Therefore,it is particularly important to explore the water ecological characteristics of RC.This study taken crayfish monoculture system（CM）as control,based on the traditional ecological investigation and high-throughput sequencing technology,analyzed the feature,dynamics and relationship of water physical/chemical factors,zooplankton,water microbial communities in RC.With these results,we can further optimize the integrated technology,improve resources and energy utilization rate,purify the environment,and ensure the sustainable development of RC.The main results and conclusions of this study were list follows:1.In order to explore the characteristics of water physi-chemical factors of rice-crayfish integrated system,we monitored the water temperature（WT）,p H,total nitrogen（TN）,total phosphorus（TP）,ammonia nitrogen（NH₄⁺-N）and nitrite nitrogen（NO₂^--N）of RC and CM.The results were list fellows:the annual average WT in RC and CM were23.54±8.52℃and 24.18±8.83℃,respectively.The WT of RC in summer was higher than that of CM,while the WT in winter was slightly higher than that of CM.The annual average p H of water in RC was 7.84±0.38,which was lower than that of CM.Except the water p H in January was higher than 8.5,the other periods were stayed in a relatively stable and normal condition.The average content of TN,TP,NH₄⁺-N,and NO₂^--N in RC water were 1.543±1.159 mg/L,0.085±0.077 mg/L,0.285±0.247 mg/L,0.017±0.029mg/L,were lower than that in CM（1.961±1.315 mg/L、0.099±0.074 mg/L、0.292±0.202 mg/L、0.026±0.051 mg/L）.Affected by fertilization,the TN,TP,NH₄⁺-N,and NO₂^--N of water in RC were all higher during July to June,then decreased rapidly.These results indicated that the growth of rice plants could purified the water environment.Above all,rice-crayfish integrated could enhance the utilization ability of substances,improve the self-purification ability,optimize the water quality,reduce the adverse impact on crayfish,and provide a more suitable water environment for crayfish culturing.Through the annual dynamic changes of water physi-chemical factors,this study suggests that the water quality regulation of rice-crayfish integrated system should be strengthened from June to July and January.2.In order to explore the characteristics of zooplankton community structure of rice-crayfish integrated system,the number of species,dominant species,density,biomass and related index of RC and CM were analyzed.The results showed that RC possessed 108species of zooplankton,higher than 102 species in CM;Zooplankton species in RC and CM were dominated by rotifer（48.25%）,next by cladocera（22.81%）.Average density and biomass of zooplankton in RC were 681.94 ind/L、13.96 mg/L respectively,and which were lower than that in CM.Strong dominant species in RC was only nauplii,however,strong dominant species in CM appeared Keratella sp.,Brachionus sp.,and other eutrophication indication species.The average value of Shannon-Weiner diversity,Pielou evenness and Margalef richness index of zooplankton were 2.29,0.75,2.29 in RC respectively,which were all higher than 1.98,0.64,1.99 in CM.Therefore,the zooplankton community structure of rice-crayfish integrated system is more stable and healthier,which further shows that the water quality is better than crayfish monoculture system.3.In order to explore the characteristics of water microbial community structure of rice-crayfish integrated system,the samples were collected from the rice seedling,tillering,flowering,filling,fruiting,and rotting stages in RC and CM.Based on high-throughput sequencing technology,we analyzed the microbial diversity,community composition and common pattern,etc.The results showed that:The water microbial diversity of RC is higher than CM.Proteobacteria,Actinobacteria,Cyanobacteria,Bacteroidetes and Firmicutes were the main phylum in water of RC and CM,both with the relative abundances.Farming system,rice growth,sampling period affected the structure of water microbial community.The biomarker species of RC mainly include Synechococcales,Cyanobiaceae,while in CM mainly include Proteobacteria,Burkholderiaceae.Through the co-occurrence network,system sensitive OTU clustered in different modules and separated by system.The Bacilli taxa were sensitive to the RC,while Flavobacterium taxa were sensitive to CM.Gammaproteobacteria plays a key role in water microbial community,and has a higher richness in RC.The above results show that the rice-crayfish integrated system manipulate a healthier and stable water microbial community structure,which can improve the ability of material circulation and energy flow in the ecosystem.