Effects Of Earthworm On Soil Enzyme Activity And Microbial Community Structure Of Poplar Plantation

Under the background of global change,large soil animals have a positive regulatory effect on soil fertility,carbon storage accumulation,and agricultural and forestry productivity.As the key species of soil sustainable development,earthworm is an important decomposer,consumer and regulator in terrestrial ecosystem.Earthworms play an important role in the process of nutrient cycling by regulating soil physical and chemical properties,soil microenvironment and microbial activities.In this study,six different treatments were used to inoculate the soil of Dongtai Poplar Plantation(CK:control,T1:surface application of poplar leaf litter,T2:mixed application of poplar leaf litter,T3:single inoculation of earthworm,T4:surface application of poplar leaf litter+earthworm,T5:mixed application of poplar leaf litter+earthworm).The basic properties of the soil,the activities of enzymes related to carbon and nitrogen cycle and the structure of microbial community were measured dynamically to explore the effects of earthworm on the soil enzyme activity and microbial community structure.It is hoped to further understand the microbiological action mechanism of earthworm activity on soil carbon cycle,and provide more theoretical basis for the accumulation of soil organic carbon in poplar plantations to promote the improvement of soil fertility in poplar plantations.The results show that:(1)Earthworms in the poplar plantation of Dongtai in Yancheng are mostly epidemiological ecological groups,and the main activity range is 0-10cm in the soil.The density of earthworms and the output of earthworm feces in summer and autumn are significantly higher than those in spring and winter,and the trend of both is consistent,both are July>October>April>December,and the minimum values are 2.08 ind/m~2,6.13 g/m~2,the maximum values are 6.25ind/m~2 and 19.75 g/m~2,respectively.The number of earthworms and the output of earthworm feces in the forest stand are significantly positively correlated with soil pH and C/N ratio,but negatively correlated with soil BD,indicating that the occurrence and activity of earthworms are closely related to these soil properties.(2)Earthworms have a certain improvement effect on soil conditions,which can significantly reduce soil bulk density(p<0.05)and alkaline soil pH.Earthworms can increase the content of TC,TN and TOC in the soil,and the effect of earthworm inoculation under mixed litter is the most obvious,with increases of 16.26%,43.02%and 19.29%respectively.The interaction between litter application methods and earthworms also had significant effects on soil BD,pH,TN,and TOC;the interaction between seasons,litter application methods,and earthworms only had significant effects on soil TN.(3)SMBC and SMBC/SMBN are significantly affected by seasonal changes,while SMBN is less susceptible to seasonal fluctuations.Regardless of whether there is litter,earthworm activity has increased SMBC,SMBN and SMBC/SMBN.The SMBC and SMBN were the highest when the litter was mixed and inoculated with earthworms,with an increase of 36.56%and 24.98%,respectively.However,the application of litter and earthworms had no strong interaction with microbial biomass.(4)soil invertase,urease and catalase activities have consistent seasonal changes:compared with spring and winter,summer and autumn enzyme activities are higher.Catalase activity increased significantly in summer,and the changes in the other three seasons were not obvious.(5)Earthworm activity can significantly increase the activities of soil invertase,urease and cellulase,and the enzyme activity is the highest under the condition of mixed litter application,with increases of 50.90%,66.64%and 149.52%respectively.Earthworms will reduce the activity of soil catalase,and under the condition of litter mixed,the enzyme activity will decrease the least,which is 2.72%.The activities of invertase,urease and catalase in soil were significantly affected by the interaction of litter application and earthworm.The activities of catalase were significantly affected by the interaction of season and earthworm,and by the interaction of season,litter application and earthworm.Earthworm can greatly increase soil enzyme index and accelerate soil biochemical process.(6)The specific order of the bacterial community diversity under each treatment is T2>T4>CK>T5>T3>T1;the bacterial community richness is T2>T4>CK>T5>T3>T1;the fungal community diversity is T2>T1>T4>T3>T5>CK;the richness of the fungal community is T4>T3>T1>T2>T5>CK.Earthworms did not improve the richness and diversity of soil bacterial community,and did not change the dominant bacterial phylum,specifically Proteobacteria,Actinobacteria and Acidobacteria.Earthworms can significantly improve the diversity and abundance of fungi,and is closely related to the application method of litter.Among them,the effect of inoculating earthworms under surface application of litter is the most obvious.The dominant fungal phylum in the fungal community was Ascomycota,Basidiomycoat,Mortierellomycota and Unclassified?k?Fungi.(7)There are 24 types of functional genes in the bacterial community function,showing the richness of the soil bacterial community function.The main community functions involved are transport,metabolism and energy conversion,but the COG function in each treatment has no significant difference in composition and proportion.Different from the bacterial community function,the composition and proportion of the soil fungal community function differ greatly in each treatment.Among them,saprophytic fungi account for the largest proportion,indicating that most of the fungi in the soil are saprophytic fungi,and most saprophytic fungi are not fully resolved,indicating that the fungal community function in the soil has a certain complexity.