Soil Nutrient Availability Drives Fungal Community Structure and Function During the Transformation of Eucalypt Plantations Logging Sites in Southern China

Highly intensive eucalypt plantation management has led to nutrient imbalances in forest land, severely weakening the ecosystem's self-healing ability. Thus, restoring logging sites is urgent. Soil microorganisms, particularly fungi, are crucial in soil ecosystems for promoting nutrient cycling, regulating soil properties, and maintaining balance. Yet, how degraded logging site transformation patterns affect the structure and function of subsurface ecosystem components remains unclear. This study examined the impacts of four transformation patterns on soil physicochemical properties and fungal communities in eucalypt logging sites and their relationships. The soil dissolved organic carbon, nitrate nitrogen ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mrow><mml:msubsup><mml:mi>NO</mml:mi> <mml:mn>3</mml:mn> <mml:mo>-</mml:mo></mml:msubsup> </mml:mrow> </mml:mrow> </mml:math> _N), and available phosphorus (AP) contents in the mixed plantations of <i>Eucalyptus</i> × <i>Manglietia glauca</i> (EM) and the rotational plantations of <i>M. glauca</i> (MM) were higher than those in the slope unforested grasses and shrubs lands (GS) and the continuous-cropping eucalypt plantations (EE). Correspondingly, both EM and MM increased the relative abundances (RAs) of Mortierellomycetes and Rozellomycotina_cls_Incertae_sedis, which have a broad range of cellulose- and lignin-degrading capabilities. In contrast, EE significantly increased the dependence of eucalypt on ectomycorrhizal fungi (mostly belonging to Agaricomycetes) and reduced soil fungal network complexity and stability compared to other transformation patterns. EM and MM significantly increased saprophytic fungi RAs and showed higher fungal network complexity compared with the above two patterns. These two patterns also distinctly inhibited the proportion of soil pathogenic fungi and the soil acidification process. Mantel test and redundancy analysis showed that fungal community composition and function were jointly driven by pH, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mrow><mml:msubsup><mml:mi>NO</mml:mi> <mml:mn>3</mml:mn> <mml:mo>-</mml:mo></mml:msubsup> </mml:mrow> </mml:mrow> </mml:math> _N, and AP contents. Additionally, during the dry season, soil water content significantly influenced fungal community composition and function. These findings have important implications for restoring degraded logging sites in eucalypt plantations.