Diminished rhizosphere and bulk soil microbial abundance and diversity across succession stages in Karst area, southwest China

Soil microorganisms are important for plant nutrients and health. However, our understanding of soil microbial communities in the rhziosphere and bulk soils as plant succession stages increased in the Karst arearemains unclear. Here, we evaluated how the bacterial and fungal communities of rhizosphere and bulk soils respond to different vegetation succession stages: grassland (GR), shrubland (SH), secondary forest (SF), and primary forest (PF). The abundance and composition of bacteria and fungi were determined by qPCR and MiSeq high-throughput sequencing methods, respectively. The results showed that the abundance and diversity in rhizosphere and bulk soils were diminished among vegetation succession stages. We found that SOC led to high micrbial abundance in GR and SH during the period of primary succession stages, while AP potentially led to low abundance of microbes in the PF and SF of subsequent succession stages. Additionally, the OTUs shared by four succession stages (common OTUs) comprised approximately 87.61 - 98.90% of the total relative abundance of bacteria and fungi in the rhizosphere and bulk soils, which indicated that the composition of fungi and bacteria in these environments were similar across different succession stages. pH might be an important driving factor involved in the similarity of bacterial and fungal compositions among different succession stages. However, the relative abundance of bacterial and fungal phyla across the four vegetation stages was different, and also determined by multiple soil properties. pH was the main factor determining bacterial community structure in rhizosphere soils, whereas SOC was the principal determinant of the same parameter for bacteria in bulk soils, and in both the rhizosphere and bulk soils for fungi. Overall, our results suggested that bacterial and fungal communities in the rhizosphere and bulk soils diminished with vegetation stages, which may provide evidence that mechanisms underlying the soil microbe-driven vegetation succession in the Karst area of southwest China.

Automated summary

The study showed that as vegetation succession stages increased, the abundance and diversity of microbial communities in both rhizosphere and bulk soils decreased. Soil organic carbon (SOC) may lead to higher microbial abundance in grassland and shrubland during the primary succession stages, while available phosphorus (AP) may result in lower abundance of microbes in secondary forest and primary forest during subsequent succession stages. The composition of bacteria and fungi in different succession stages was found to be similar, with pH possibly playing a key role in driving this similarity.