Effects Of Rice-duck Systems With Different Farming Years On Soil Enzyme Activity And Bacterical Community Structure

Rice-duck farming technology has a long history of development in China.It uses the symbiotic relationship between rice and ducks to build a three-dimensional planting and breeding complex ecosystem.It has obvious advantages in improving the utilization efficiency of agricultural resources,stabilizing the output of agricultural products,optimizing the quality of agricultural products,and increasing the economic income of farmers.The predecessors have conducted a lot of research on the rice-duck farming ecosystem,but mainly concentrated on the soil physical and chemical properties,water environment and economic benefits,etc.,but there are few studies on the response of the soil microbial characteristics to the rice-duck farming model.In this study,we set up three types of paddy fields:no rice-duck farming(CK),short-term rice-duck farming(SRDF),and long-term rice-duck farming(LRDF).Relying on advanced technology such as high-throughput sequencing method,had carried out two years of soil microbial ecosystem research.From the perspective of soil enzyme and bacterial,the effects of three rice-duck farming modes on soil enzyme activity and bacterial community reconstruction at different growth stages of rice were systematically studied.The ecological mechanism of rice duck farming model affecting soil bacterial community construction was comprehensively discussed,which provided scientific theoretical basis for soil nutrient transformation and balance under the long-term rice duck farming model.Main conclusions are as follows:(1)The effect of rice-duck farming on soil improvement was obvious,which was as follows:LRDF>SRDF.Compared with CK,after long-term rice-duck farming and short-term rice-duck farming,soil bulk density decreased by 7.8%and 2.5%,and total porosity increased by 5.3%and 1.7%,respectively.Long-term rice-duck farming was more conducive to improving the physical structure of the soil.The rice-duck farming made the soil pH value fluctuate in the range of 5.6-6.2,which effectively maintained the soil pH balance and stabilized the living environment of soil microorganisms.In terms of soil nutrients,after long-term rice-duck farming and short-term riceduck farming,the soil organic matter content increased by 22.7%and 7.8%respectively,the total nitrogen content increased by 24.0%and 12.8%respectively,and the nitrate nitrogen content increased by 16.5%and 12.9%respectively.The soil ammonium nitrogen content of long-term riceduck farming field increased by 7.3%compared with no rice-duck farming field,the content of available potassium increased by 4.7%and 1.7%respectively compared with no rice-duck farming field and short-term rice-duck farming field,the content of available phosphorus in the soil increased by 4.2%compared with the no rice-duck farming field.(2)There were differences in soil enzyme activities in rice-duck system with different farming years.Among them,the activities of catalase and alkaline phosphatase in short-term rice-duck farming field were 3.6%and 3.3%higher than those in no rice-duck farming field,while in longterm rice-duck farming field decreased by 3.7%and 3.6%,respectively.Short-term rice-duck farming could increase the activities of catalase and alkaline phosphatase,but with the increase of farming years,the activities of the two enzymes decreased.Moreover,different rice growth stages had great effects on the activities of the two enzymes,which showed as follows:heading>maturity.Short-term rice-duck farming had little effect on soil urease,but long-term rice-duck farming field soil urease activity increased by an average of 1.9%in the two periods.Rice-duck farming had a greater impact on soil invertase activity.At heading,the soil invertase activity of long-term rice-duck farming field and short-term rice-duck farming field significantly increased by 17.9%and 16.5%,respectively,and the maturity increased by 12.5%and 8.3%,respectively.There were also some differences in the effects of different rice growth stages on enzyme activity.The activity of urease was in the order of heading>maturity,while the activity of invertase was in heading<maturity.(3)Under the rice-duck farming model,the soil bacterial community in the plow layer of the rice field was more complex than that of the no rice-duck farming field,and the community richness and diversity index were higher.Rice-duck farming could increase the number of unique microbial species in the soil,and the levels of OTU,phylum and genus were increased by 6.4%,2.6%and 3.2%,respectively,enriching the interaction between soil bacteria.Among them,the soil bacterial community structure and composition in the short-term rice-duck farming field were relatively active.With the increase of the total farming years,the soil bacterial community began to stabilize.Chloroflexi and Proteobacteria were the dominant bacteria in the rice-duck farming system.Because of the high relative abundance of bacteria involved in soil carbon and nitrogen cycle,it was beneficial to improve the cycle efficiency,thus ensuring the safety and stability of the soil environment.Compared with the short-term rice-duck farming field,the soil bacterial richness in the long-term rice-duck farming field increased by 0.9%,and the diversity decreased by 0.2%.Although the change was not obvious,the structure of soil bacterial community was more stable and had stronger anti-interference ability to external adverse factors.(4)Soil enzyme activity was affected by many factors,and the main factors were soil organic matter,ammonium nitrogen,nitrate nitrogen and pH.Organic matter,ammonium nitrogen and nitrate nitrogen were the driving factors to promote the overall variation of enzyme activity,they were positively correlated with the activities of urease and invertase.Long-term rice-duck farming caused a slight decrease in soil acidity,which had a certain inhibitory effect on soil alkaline phosphatase activity.Catalase activity was negatively correlated with organic matter,ammonium nitrogen and nitrate nitrogen.In addition to soil environmental factors,enzyme activity was also greatly affected by microorganisms,in which the effect of soil bacterial richness and diversity on the activity of alkaline phosphatase and catalase showed positive correlation,and the effect on the activity of invertase and urease showed negative correlation.(5)The structure of soil bacterial community was greatly affected by soil environment.The environmental factors that caused the variation of the bacterial community structure in the soil of rice-duck farming were mainly organic matter,total nitrogen,bulk density and pH value,etc.The influence of different dominant bacterial phylums also had certain differences.Actinobacteria,Firmicutes and Gemmatimonadetes were greatly affected by the contents of nutrients such as soil organic matter,total nitrogen and available potassium.Nitrospirae and Bacteroidetes were not only affected by the soil nutrients,but also affected by pH value.The results of network structural analysis showed that in addition to the effects of organic matter,total nitrogen and pH values,there were also some interactions among different genera of bacteria.In the rice-duck farming system,there was a high association between Gemmatimonas and Nitrospira and other bacterial genera.The structural equation model showed that different rice-duck farming models directly changed the soil organic matter,C/N,bulk density and pH value,and then brought some indirect positive or negative effects on the bacterial community.Long-term rice-duck farming significantly increased soil organic matter,but did not significantly increase bacterial richness and diversity,and significantly decreased bacterial diversity due to the significant decrease of C/N.Although different rice-duck farmin years had little effect on pH,slight changes in soil acidity and alkalinity significantly affected the diversity of bacterial diversity.The above results provide guidance for the development of long-term rice-duck farming model.