Unravelling the role of soil microflora from micro and macro aggregates in plant growth during primary and secondary successions

The role of microbial communities from soil aggregates in grasses and herbs' development during plant suc-cession is not clear. We isolated microbial communities in micro-(<250 mu m) and macro-aggregates (>250 mu m) and investigated their inoculation on plant communities. Microbial inoculums were added to sterilized soil substrates from primary and secondary plant succession. Soil substrates were collected from primary plant succession included early (ca. 10 years) and late (ca. 65 years) substrates, and secondary plant succession included ancient permanent meadows since the last few thousand years and the same soils restored by secondary succession after being used as arable land.Results showed that during primary plant succession, the late substrates had higher plant biomass than the early substrates, especially when they received microbial communities from the early substrates. When trans-ferred from donor to recipient substrates, bacterial community structure was depending both on the donor and recipient soil, but fungal community structure was mainly controlled by the donor soils and soil aggregates. Micro-aggregate inoculum from the early substrates promoted the growth of herbs, while macro-aggregate inoculum increased the growth of grasses in the late substrates.In contrast, plants grew better during secondary plant succession in ancient and restored soils when they retained their original microbial communities. Inoculum from the ancient soils did not benefit plant growth in the restored soils. Macro-aggregate inoculum from the restored soils had higher plant biomass than micro -aggregates in the ancient soils. Structural equation modelling showed that bacterial community composition (e.g. actinobacteria) significantly controlled total plant community biomass in the primary successional substrates.Overall, our study showed the effect of microbial community in soil aggregates on grasses and herbs' com-munity development.