The shifts in soil microbial community and association network induced by successive planting of Eucalyptus plantations

• Successive planting of Eucalyptus reduces soil multifunctionality and fungal diversity. • Microbial network complexity declines with increasing planting generations. • Successive planting causes shift from soil C-using to N-using bacteria. • Successive planting causes shift from saprophytic fungi to symbiotic fungi. Successional planting of Eucalyptus is known to significantly affect soil quality. However, the accompanying changes in the bacterial and fungal community structure, co-occurrence network pattern, and microbial functions are unclear. This prevents a full assessment of the impact of successional planting patterns on soil ecosystem services. In this study, we investigated the effect of replacing Pinus massoniana plantations with multi-generational successional planting of Eucalyptus on soil bacterial and fungal communities. The results showed that it elicited significant declines in soil multifunctionality and the diversity and richness of the fungal community, together with a significant increase in soil bulk density. The third and fourth-generation plantations had notably reduced microbial network complexity, robustness, and association between microbial taxa. Successional planting also significantly changed the relative abundance of dominant microbial groups at the phylum and order levels, which subsequently caused dramatic changes in microbial functions. With successive planting generations, the soil bacterial community shifted from carbon-using to nitrogen-using bacteria, and the fungal community shifted from saprophytic and pathogenic to symbiotic fungi. From the above results, we concluded that multi-generation plantation of Eucalyptus has a significant negative impact on soil multifunctionality and microbial community, and after two generations of successive planting, it should be considered to change the plantation management pattern. This work provides a theoretical reference for the sustainable management of Eucalyptus plantations.