Soil microbial community structure and diversity in different successive planting generations of Eucalyptus plantations

To explore the effects and driving mechanisms of successive planting on soil microbial communities in Eucalyptus plantations.

Using high-throughput sequencing, this study analyzed the structure and diversity of soil bacterial and fungal communities across four successive planting generations of Eucalyptus urophylla×E. grandis plantations in Leizhou peninsula. By combining with the determination of soil chemical properties, the interlinkages between soil microorganisms and environmental factors were also elucidated.

1) Although fungal ACE, Chao1, and Shannon indices in the 40-80 cm layer were significantly higher in G2 than in other generations, successive planting exerted no significant effect on soil microbial alpha diversity. However, it significantly altered microbial community structures; 2) In all soil layers, the dominant bacterial phyla in each generation were Pseudomonadota, Acidobacteriota, Chloroflexi, and Actinomycetota, while the dominant fungal phyla were Basidiomycota and Ascomycota. In the 0-40 cm soil layer, with successive planting generations, the relative abundance of the soil bacterium Candidatus_Eremiobacterota significantly increased, in contrast to significant decreases in Bacteroidota. In terms of fungal community, the relative abundance of Ascomycota exhibited a pronounced downward trend, whereas Basidiomycota showed an initial decrease followed by an increase, with significant intergenerational differences in abundance; 3) Findings from correlation and redundancy analyzed indicated notable interconnections between soil microbial communities and physicochemical properties. Soil pH, available nitrogen (AN), available phosphorus (AP) and available boron (AB) were identified as key environmental factors driving the evolution of soil microbial community structure; 4) The results of partial least squares path model (PLS-PM) showed that successive planting had a significant direct negative effect on soil chemical properties, and further had a significant impact on the composition, structure and diversity of soil bacterial and fungal communities through direct or indirect effects.

This study reveals the evolution patterns of soil microbial community structure and diversity in different successive planting generations of Eucalyptus plantations, providing theoretical foundation for soil amelioration and sustainable silvicultural management of plantations.