Soil bacteria and fungi respond differently to plant diversity and plant family composition during the secondary succession of abandoned farmland on the Loess Plateau, China

Aims This study aimed to determine the responses of soil bacteria and fungi to plant species diversity and plant family composition (PFC) following secondary succession on former farmland (FL). Methods Illumina sequencing of 16S rRNA and ITS genes was used to determine soil microbial communities along a chronosequence of FL left abandoned for 0, 10, 20, 30, 40, and 50 years on the Loess Plateau. Soil properties, plant diversity, and PFC were also investigated. Results Fungal communities were dominated by Ascomycota and Basidiomycota . Fungal diversity and Ascomycota abundance increased with time, while Basidiomycota abundance decreased. The fungal diversity and dominant phyla were related to the increasing levels of plant species diversity and evenness with succession. Bacterial diversity first increased and then decreased as succession proceeded, peaking at 30 years. Bacterial communities transitioned from Actinobacteria to Proteobacteria dominance during the first 30 years, after which Actinobacteria was dominant. Plant family composition exerted indirect effects on the diversity and dominant phyla of bacterial communities, mainly through direct effects on soil organic carbon and total nitrogen content. Bacterial diversity and Proteobacteria abundance were higher at Leguminosae- and Gramineae-dominant succession stages, but lower in Compositae-dominant plots; Actinobacteria showed the opposite result. Conclusions Plant species diversity and evenness might be the key drivers for shaping fungal communities, but bacteria are influenced more by changes in PFC and abiotic soil nutrient levels during succession.