Effects Of Different Bioavailability Of Carbon Sources On Vermicomposting And Its Microbial Community Structure

Organic solid waste production is huge in tropical areas of China,and the realization of solid waste resourceization is an important element of green and sustainable development of society.Vermicomposting is a biotransformation technology to treat organic solid waste,which can realize the reduction,harmlessness,resourceization and value-added of crop straw,livestock manure and other waste.Rational formulation of composting raw materials is a prerequisite for efficient vermicompost conversion.However,the current traditional formulation of raw materials for earthworm compost relies on mass ratio,volume ratio or total C/N index,ignoring the variability of bioavailable components(mainly organic matter components of carbon source)among different raw materials,leading to problems such as uneven reproductive effects of earthworms and differences in the quality of earthworm manure.Therefore,in order to clarify the effects of different bioavailable carbon sources on earthworm composting,this study is intended to investigate the effects of different bioavailable carbon sources on the growth and reproduction of earthworms and the quality of earthworm composting based on the classification of bioeffective components of waste materials.The results of the study can be used in the context of conventional C/N fertilization.The results of the study can provide new insights and understanding for the scientific and precise formulation of efficient composting materials for earthworms based on conventional C/N,which is important for improving the processing efficiency of vermicomposting.1.Classification of bioavailability attributes of tropical agricultural wastes.In order to clarify and classify the bioavailability of organic wastes in different thermal zones and to carry out the evaluation of the effectiveness of vermicomposting based on bioavailable attributes,this study tested and analyzed the carbon and nitrogen available effective fractions of 19 types of typical wastes in the thermal zone using the acid hydrolysis method and classified the waste utilization attributes using the cluster analysis method.The results showed that based on C/N and bioavailability of organic matter carbon sources(i.e.,active carbon fraction LCP1,LCP2 content),the bioavailability attributes of carbon source materials could be classified as: difficult to utilize carbon sources(pine wood chips,rubber wood chips,tomato straw,pepper straw),moderate to utilize carbon and nitrogen(rice straw,corn straw,cowpea straw),and easy to utilize carbon sources(pineapple peel residue,mango peel residue).On this basis,four types of carbon source materials with different bioavailability levels from high to low representativeness were selected: pineapple peel residue,rice straw,tomato straw,and rubber wood shavings as external carbon sources for vermicomposting experiments.2.Effects of different bioavailability of carbon source components on the growth and reproduction of earthworms and compost quality.In this study,cattle manure was selected as the N source,and pineapple peel residue(high),rice straw(medium),tomato straw(low),and rubber wood chips(very low)were selected to be mixed with cattle manure to form four C/N(24,30,36,42)raw materials,and pure cattle manure was used as the control group to construct a vermicomposting model with different bioavailability carbon sources,and a 60-day vermicomposting experiment was conducted.The results showed that The results showed that the optimal C/N of adding different types of bioavailability carbon sources was different under the evaluation of the comprehensive target of earthworm growth and reproduction.The maximum total weight of adult earthworms(9.01 g)was achieved at 86.80% of raw material active carbon availability(ACC),and the maximum number of young earthworms(375)was achieved at 42.54% of raw material inactive carbon fraction(RCP).under the optimal C/N condition,the increase in the proportion of easy-touse carbon source promoted the increase of earthworm weight,while the increase in the proportion of difficult-to-use carbon source was added to promote earthworms to reproduce and increase their numbers.Under the conditions of adding optimal C/N for different bioavailability carbon sources,the percentage of ACC,the efficient component of bioavailable carbon sources in the compost material,ranged from 52.69 to 60.02%,and the best overall condition of earthworm growth and reproduction was achieved.Different bioavailability carbon sources had significant effects on the quality of vermicompost.When the difficult-to-use carbon source(rubber wood chips)was added,the feedstock ACC was at 37.05% with the highest TOC fixation rate of 59.3%,and the highest humification index and humification rate were at 53.38% with 40.79% and 40.80%,respectively.The feedstock ACC was positively correlated with nutrient content,humus content and hemicellulose content,and the percentage of non-reactive carbon fraction(RCP)in the feedstock was positively correlated with lignin and cellulose content.on the basis of C/N optimum,appropriately increasing the percentage of RCP,a difficult-to-use carbon source fraction,could improve the TOC fixation rate of vermicompost,while appropriately increasing the efficient rate of easy-to-use carbon(ACC1)could improve the vermicompost TN fixation rate.The comprehensive evaluation showed that the best overall quality of vermicompost was achieved when the ACC in the raw material was between 46.14 and60.02% for different bioavailability carbon sources added with the optimal C/N conditions.3.The addition of different bioavailability carbon sources had a significant effect on the structural composition of the microbial(bacterial)community of vermicomposting,with the total abundance of the five phyla Proteobacteria,Bacteroidetes,Actinobacteria,Chloroflexi,and Firmicutes accounting for more than 90% of the total abundance in each treatment group and being the total abundance of the five bacterial phyla,Actinobacteria,Chloroflexi and Firmicutes,was more than 90% in each treatment group and were the major bacterial flora of vermicompost.The external addition of carbon sources led to a certain decrease in the diversity and abundance of bacterial communities in vermicomposting;the KEGG results showed that the addition of carbon sources with low bioavailability(tomato straw,rubber wood chips)induced the expression of more genes related to carbon metabolism,and the addition of carbon sources with high bioavailability(pineapple peel residue)induced the expression of more genes related to amino acid metabolism.The easyto-use carbon efficiency(ACC1)and medium-use carbon efficiency(ACC2)were positively correlated with the abundance of Proteobacteria and Bacteroidetes,while the percentage of raw material inactive carbon fraction(RCP)was positively correlated with the abundance of Actinobacteria,Chloroflexi and Firmicutes The relationship was positive.The different bioavailability of carbon fractions induced the microbial(bacterial)community in the vermicomposting system to develop selectively towards different degradable feedstocks and to achieve efficient conversion of waste with the coupling effect of microbial mediation and earthworms.