Shifts in microbial- and plant-derived biomass degradation genes with afforestation promoting carbon accumulation.

Microorganisms decompose plant residue in soil and incorporate it to their biomass, thereby promoting soil carbon (C) accumulation. However, the mechanisms underlying microbial-mediated plant- and microbial-derived C degradation and their response to afforestation remain unclear. Here, soil organic C (SOC), carbohydrate-activated enzymes (CAZymes), and C acquiring enzyme were utilized to investigate microbial-mediated SOC formation after afforestation (3, 7, and 10 years) in an arid region, with uncultivated wasteland serving as the control (0 years). Results showed that the relative abundance of microbial CAZymes degrading plant-derived C (cellulose, hemicellulose, lignin, 90.87-91.72 %) exceeded that degrading microbial-derived C (8.28-8.13 %). Additionally, CAZymes degrading bacterial-derived C (peptidoglycan, 6.60-7.46 %) was higher than that degrading fungal-derived C (chitin and glucans, 1.37-2.20 %). Intriguingly, temporal dynamics revealed non-linear dynamics-SOC content, enzyme activities, and plant-/microbial-derived C peaked at 7-year of afforestation before declining in 10-year of afforestation. Afforestation reduced the abundance of genes degrading plant-derived C, including cellulose- and hemicellulose-specific gene families. In contrast, the abundance of genes degrading bacterial-derived C showed a decreasing and then increasing trend as afforestation, while genes degrading fungal-derived C showed the opposite trend. In summary, afforestation-induced changes in soil nutrients alter the abundance of microbial functional genes degrading bacterial-, fungal-, and plant-derived C, thereby influences SOC dynamics through these C components. These findings underscore the significance of the relationship between functional genes and microbial metabolism in SOC accumulation.