| Traditional compost is generally faced with the problems of low fermentation efficiency and nutrient retention ability,due to the existence of refractory organic matter,such as lignocellulose.This makes the quality of compost products poor,and the expected environmental and economic benefits can not be realized effectively.In sum,it is urgent to explore appropriate strategies to promote the degradation of lignocellulose and improve the degree of humification of compost.In previous studies,effective microorganisms(EM)agent has been evidenced that it had a positive potential to promote the degradation and humification of organic matter in compost.However,a competition between exogenous and native microorganisms has been frequently found in previous studies,which weakened the application efficiency of EM agent,even caused a counterproductive result.Biochar has been shown that it can accelerate the composting process via effectively regulating the metabolism of microbial community,due to its large specific surface area and developed pore structure.Hence,it is reasonable to assume that biochar and EM agent may have a synergistic effect on the improvement of lignocellulosic degradation.However,this aspect was rarely studied in previous studies,and the improvement potential and underlying mechanisms are unclear.Furthermore,the potential impacts of compost product on soil nutrient release and plant growth are the key aspects to the successful usage of compost in practice.However,whether the compost combinedly amended with biochar and EM has greater potential for improving soil nutrient release potential and plant growth is also unknown.Considering the shortcomings of the current studies,three main contents were carried out in this study: i)by designing a lab-scale composting experiment,the effects of the combination of biochar and EM agent on the degradation of lignocellulose and humification of compost were systematically explored;ii)by designing an indoor soil incubation experiment,the effect of different un-amended compost and CSB/EM amended compost on the nutrient release potential of soil was examined,and whether the amended composts had a greater improvement of soil nutrient release potential and the underlying mechanisms were also determined;and iii)by conducting an indoor plant pot experiment,the effects of CSB-EM compost product on plant growth and the related mechanisms were further investigated and the optimal amount of compost addition was determined.The main results are as follows:(1)CSB and EM used alone or in combination can effectively improve the humification degree of compost and the stability of compost products.All the additive practices were found to significantly elevate the degradation degree of lignocellulose.The degradation rates of cellulose,hemicellulose,and lignin in different additive treatments were 20.8%–31.2%,36.2%–44.8%,and 19.9%–25.7%,respectively,which were greatly higher than those determined in the control.Compared with the single uses of CSB or EM,the combined use of CSB and EM generated greater promotions in degradation of lignin and hemicellulose and increase of humic acid content.By comparing the differences in microbial communities among different treatments,the CSB-EM demonstrated greater increases in activity and diversity of lignocellulose degradation-related microbes,especially for fungus,which could be the important reason for the enhanced degradation of lignocellulose.(2)Compared with un-amended compost product,the amended composts(CSB-C,EM-C and CSB+EM-C)can significantly improve the nutrient content in coastal wetland soil,among which the CSB+EM-C had a greater potential.Integrating the results of net mineralization rate,nutrient release rate,and DOM quality measured in coastal wetland soil added with different amended composts,the CSB+EM-C was found to have a better improvement effect.Compared with the other two composts(CSB-C and EM-C),the CSB+EM-C showed a greater increase in the relative abundances of Protepbacteria,Firmicutes,Bacteroidetes,and Actinobacteria,which were the nutrient conversion-related microbes.(3)The CSB-EM compost added at different amounts all demonstrated significant increases in the biomass and nutrient uptake quantity of different parts of Sesbania,especially for the 4% addition rate.The CSB-EM compost improved the physical and chemical properties of rhizosphere soil,enhanced the humification degree of DOM in rhizosphere soil,and accelerated the rate of rhizosphere nutrient conversion,among which the 4% addition rate displayed a higher nutrient supply efficiency.Compared with the other two addition rates(2% and 8%),the 4% addition rate had the greatest potential to elevate the relative abundances of Proteobacteria,Bacteroidetes,Chloroflexi,Firmicutes,and Actinobacteria.This could be the key mechanism of 4% addition rate for the enhanced soil nutrient conversion and plant uptake,and the consequently increased plant biomass.(4)Based on the study results of(1),(2),and(3),the combined use of CSB and EM in aerobic compost production was proved to be an effective technical strategy for simultaneously achieving the resource utilization of organic waste and the improvement of degraded soil in coastal wetlands.It is highly recommended to combinedly use CSB and EM to organic compost production to obtain higher economic and environmental benefits. |
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