Additives Change Microbiota to Promote Humic Acid Formation in Composting of Vegetable Wastes

Vegetable wastes in general do not compost well due to their high moisture content (MC) and low dry mass. To overcome these obstacles, in this study co-composting of Chinese cabbage wastes (CA) or celery wastes (CE) with corn stover and sheep manure was utilized to improve the composting performance, and the effects of the additives on microbiota during composting and microbial degradation of lignocellulose and synthesis of humic acid (HA) were investigated. The results showed that addition of 25 % corn stover or 40 % sheep manure increased hemicellulose, cellulose and lignin destruction by 24.6 %- 29.9 %, 5.5 %- 14.0 % and 8.3 %- 17.3 %, respectively, and produced 20.5 %- 48.9 % more humic acid (HA). LEfSe analysis found that addition of 25 % corn stover or 40 % sheep manure promoted growth of lignocellulose-degrading microorganisms alongside with the transformation of anaerobic fermentation into aerobic fermentation, and analyses of bacterial and fungal functions testified that the addition of corn stover or sheep manure increased microbial activities related to aerobic chemoheterotrophy, lignocellulosic degradation and activities of saprotroph at different stages. Mantel test showed total organic carbon (TOC), moisture content (MC) and EC were positively correlated to bacterial biomarker and fungal biomarker, which were also significantly correlated to HA. The addition of 25 % corn stover or 40 % sheep manure was very effective in ameliorating the aeration state and provide alternative carbon sources during composting to promote growth of lignocellulose-degrading microorganisms, which increased lignocellulose degradation and saprophytic activities to accelerate the synthesis of HA.