A less complex but more specialized microbial network resulted in faster fine-root decomposition in young stands of Robinia pseudoacacia

Microorganisms play an important role in litter decomposition. Bacteria and fungi colonize litter during the decomposition process; therefore, understanding the interactions of bacterial and fungal communities can yield insight into litter decomposition dynamics. Most studies have focused on leaf litter decomposition, but thus far, there has been little information on the dynamic changes in soil microbial composition at the different stages of fine-root decomposition. Therefore, we conducted a 210-day incubation experiment on the fine roots of Robinia pseudoacacia to explore how the temporal dynamics of soil enzyme activities and microbial communities are related to the decomposition of R. pseudoacacia at four different stand ages (15, 25, 35 and 45 years) during vegetation restoration. The results showed that the fine-root decomposition rate was higher for young stands of R. pseudoacacia. We found that the oxidase activity was significantly higher in the young stands (15 and 25 years) than in the old stands (35 and 45 years), while the hydrolase activity showed the opposite trend. The main reason for the higher decomposition rate in young stands of R. pseudoacacia was the high oxidase enzyme activities and less complex but more specialized microbial network of younger stands. The occurrence network was used to identify the keystone taxa by statistical analysis, and the key taxa changed from Acidobacteria to Proteobacteria during vegetation restoration. These findings demonstrate that vegetation restoration alters the soil microorganism community and network structure during fine-root decomposition of R. pseudoacacia. This finding is of great significance for understanding the role of microorganisms in regulating fine-root decomposition dynamics.