Characteristic Analysis Of Dissolved Organic Matter And Microbial Communities In Common Vermicompost

As production of organic waste increase,the problem of environmental pollution is becoming more and more serious.Traditional treatment methods have high energy consumption and pollution.Vermicomposting is a method that uses earthworms and microorganisms to efficiently degrade organic waste.The vermicomposting product,vermicompost,contains rich nutrients such as nitrogen,phosphorus,and potassium,and beneficial soil microbial communities.In addition,vermicompost has a good granular structure and porosity,making it highly valuable in various fields.Many studies showed that properties of vermicompost are greatly influenced by the substrate.However,there is lack on the investigation of dissolved organic matter and microbial communities in common vermicompost in China.In this study,37 kitchen waste,sludge and cow dung vermicompost were collected to analyze physicochemical properties,dissolved organic matter（DOM）structure and microbial communities,and explore the relationship between the differences in vermicompost substrate,dissolved organic matter and microbial communities.The main results are as follows:（1）The analysis of physicochemical properties showed that the p H values of 3vermicomposts were close to neutral.Electrical conductivity in 60%kitchen waste,75%sludge and 36.8%cow dung vermicompost met agricultural standards（NY525-2021）.More than half of vermicompost samples did not meet the agricultural standard for moisture content（NY525-2021）.The sludge vermicompost had the highest ammonia nitrogen,nitrate nitrogen and dissolved phosphorus content among 3 vermicomposts,with median values of 287.78 mg/kg,2019.98 mg/kg and 674.55 mg/kg,respectively.Normal distribution showed that the nutrient content distribution of sludge vermicompost was the most concentrated and least affected by substrate differences,with the most stable properties.However,there were no significant differences in physicochemical properties（P>0.05）.（2）The results of DOM analysis showed that the DOM content in 3 vermicomposts were around 3000 mg/kg,with no significant difference（P>0.05）,but the coefficient of variation of kitchen waste vermicompost was the smallest.Three-dimensional fluorescence analysis showed that 60%,58%and 50%samples from kitchen waste,sludge and cow dung vermicompost had obvious fluorescence characteristic peaks of fulvic acid and humic acid,respectively.The fluorescence peak intensities representing fulvic acid and humic acid were both highest in kitchen waste vermicompost.The results of fluorescence regional integration（FRI）showed that the conversion efficiency of protein-like substances to humic-like substances in sludge vermicompost was higher.Parallel factor analysis（PARAFAC）separated component1 representing humic-like substances and component 2 representing protein-like substances from 3 vermicomposts.The F_max of component 1 in sludge vermicompost was 61.54%and101.37%higher than that in kitchen waste and cow dung vermicompost,respectively.The F_maxof component 2 was 21.67%and 43.33%lower than that in kitchen waste and cow dung vermicompost,respectively.The biological index（BIX）,humification index（HIX）and freshness index（β:α）in sludge vermicompost were all the highest,indicating that DOM in sludge vermicompost mainly came from autogenous sources,with the most stable DOM structure and the highest biological activity.（3）High-throughput sequencing results showed that the dominant phyla in 3vermicomposts were Proteobacteria,Bacteroidetes,Actinobacteria and Firmicutes.However,3vermicomposts had specificity in dominant genera.Alpha diversity showed that the Chao1,Shannon and Simpson indices in cow dung vermicompost were all the highest among 3vermicomposts,while the Shannon and Simpson indices in sludge vermicompost were the smallest and the Chao1 index in kitchen waste vermicompost was the smallest.This indicates that the microbial community in cow dung vermicompost has both high species richness and high species diversity.Beta diversity showed that the microbial community structure of kitchen waste and cow dung vermicompost had a high degree of similarity,while sludge vermicompost had significant differences from the other 2 vermicomposts（P<0.05）.The metabolic pathways of 3 vermicompost were mainly cellular processes,with human diseases having the smallest proportion.（4）Redundancy analysis（RDA）results showed that organic matter and DOM content were significantly positively correlated with Proteobacteria,while NO₃^-was significantly negatively correlated with Proteobacteria.Proteobacteria are more likely to survive and reproduce in environments with high organic matter and DOM content,while being inhibited in environments with high NO₃^-content.Bacteroidetes were positively correlated with moisture content and significantly negatively correlated with p H,NH₄⁺and dissolved nitrogen content.Bacteroidetes are more likely to survive and reproduce in environments with high moisture content,while being inhibited in environments with high p H,NH₄⁺and dissolved nitrogen content.Proteobacteria and Firmicutes are negatively correlated,Bacteroidetes and Actinobacteria are negatively correlated.