Combined application of straw and bio-organic fertilizer improved organic carbon sequestration efficiency and carbon pool management index of degraded Mollisol

Application of bio-organic fertilizer is an important method for the restoration of carbon pool in degraded Mollisol. However, the changes in sequestration efficiency and carbon pool quality caused by the combined application of straw and different amounts of bio-organic fertilizer are still unclear. In this study, field experiments of straw returning and straw combined with low (SLM, 600 kg C ha -1 ) and high amount of bio-organic fertilizer (SHM, 2400 kg C ha -1 ) were carried out in Northeast China. The remediation effect of straw combined with bio-organic fertilizer on degraded Mollisol was evaluated by analyzing soil organic carbon components, carbon sequestration efficiency, carbon pool management index and microbial community changes. The results showed that SHM treatment achieved the highest carbon sequestration efficiency (29.9%) and increased carbon pool management index. Straw combined with high amount of bio-organic fertilizer treatment increased the richness of bacterial community, the activity of β-glucosidase and cellobiohydrolase, and up-regulated the fungal cofactor biosynthesis, promoting stable carbon accumulation by altering microbial metabolic pathways toward biosynthesis. Compared with the control group, the mineral-associated organic carbon and refractory organic carbon increased by 20.4% and 22.0%, respectively ( P < 0.05). In contrast, straw combined with low amount of bio-organic fertilizer treatment reduced microbial diversity, and up-regulated the fermentation and TCA cycle, leading to carbon mineralization. In conclusion, straw combined with high amount of bio-organic fertilizer can promote stable carbon pool accumulation by regulating microbial community structure and metabolic function, thus effectively improving the carbon sequestration potential and quality of degraded Mollisol. • High amount of bio-organic fertilizer can achieve efficient carbon sequestration; • Carbon in low amount of bio-organic fertilizer showed ' high turnover, low fixation '; • Low amount of bio-organic fertilizer increased the potential risk of carbon loss; • Microbes drive carbon pool management index, stable carbon dictates sequestration.