Key bacterial, fungal, and protist taxa regulate nutrient availability during vegetation restoration under different climate conditions in karst soil

To determine the mechanisms underlying the response of microbial interactions to vegetation restoration under different climate conditions, we examined the changes occurring at two temperature levels in soil bacterial, fungal, and protist microbiomes under a reference cropland and a plantation forest and a shrubland. Bacterial and protist diversity levels in the high-temperature region of Guangxi (20.9 °C) were higher in cropland than in shrubland or plantation forest. By contrast, fungal richness was lower under cropland than shrubland. The bacterial phyla Cyanobacteria, Gemmatimonadetes, and Nitrospirae, the fungal taxa Ascomycota and Mucoromycota, and the protist groups Ciliophora, Lobosa, and Ochrophyta had lower abundance under vegetation restoration than cropland. There were no significant differences between shrubland and plantation forest in terms of bacterial, fungal, or protist diversity or community composition. A co-occurrence network revealed higher numbers of correlated links among bacterial, fungal, and protist taxa in the low-temperature region of Guizhou (14.6 °C) than Guangxi. Stronger interactions were observed among microbial taxa under cropland than under vegetation restoration. Protist groups Cercozoa and Lobosa showed the highest numbers of links with bacterial phyla Acidobacteria and Proteobacteria and with fungal phylum Ascomycota. Hence, a strong food web existed among these microbiomes. Proteobacteria, Acidobacteria, Ascomycota, and Cercozoa were correlated with soil nutrient levels. Therefore, these dominant taxa determined nutrient availability. The predation of bacteria and fungi by protists was more intense at low temperature than high temperature. Key bacterial, fungal, and protist groups, their co-occurrence networks, and environmental temperature influence soil nutrient accumulation during vegetation restoration.