Mixing with Schima Superba Enhanced Soil Fertility and Simplified Soil Microbial Community of Eucalyptus Urophylla Forests

This study focuses on how the native broad-leaved tree species, Schima superba (Ss), influence the belowground ecological environment of the long-time pure Eucalyptus culture plantations (PCP) in South China. We selected five sites from each transformation mode: the continuing pure E. urophylla (Eu) culture plantation and the introducing Ss into pure Eu culture plantation, and collected litter and soil samples. For collected samples, we measured chemical and biochemical properties, and analyzed microbial community structure using Illumina MiSeq sequencing technology to investigate the effects of the five-year Ss introduction on soil properties and microbial community of the three-generation Eu PCP mode. The introduction of Ss increased total and available nutrients levels, except for the available potassium and pH. It also enhanced bacterial community richness. The relative abundance of WPS-2 in litter and soil layers increased, while that of Bacteroidetes, Planctomycetes, and Gemmatimonadetes in the litter layer decreased. Chloroflexi became the bacterial network core in the mixed Ss with Eu culture plantations (MCP) mode, replacing Planctomycetes, the core in the Eu PCP mode. For the fungal community, the introduction of Ss increased fungal community diversity and richness in the soil layer but decreased them in the litter layer. It also reduced the relative abundance of Basidiomycota while increasing that of Rozellomycota and Mucoromycota. Ascomycota became the fungal network core in MCP mode, replacing Basidiomycota, the core in Eu PCP mode. Therefore, our findings indicated that MCP mode simplified interactions within the microbial community while enhancing soil nutrient levels, recruiting bacteria form Chloroflexi or Verrucomicrobia, and fungi from copiotrophic Ascomycota, Eurotiomycetes, Rozellomycota or Mucoromycota to mineralize soil and decompose litter.