Soil physicochemical properties play a key role in plant growth and development; however, owing to land use change and successive planting, long-term changes in soil physicochemical properties are rarely reported. The objective of this study was to analyze changes in soil physicochemical properties caused by the conversion of Masson pine forests to Eucalyptus plantations and the successive planting of first-, second-, and third-generation Eucalyptus plantations in China using a space-for-time substitution method. The results demonstrated significant differences in soil physicochemical properties between Masson pine forest (MP) and second-generation (G2) and third-generation (G3) Eucalyptus plantations at 0-20 and 40-60 cm soil depths (p<0.05). Alkaline hydrolytic nitrogen levels were significantly lower in G3 than in first-generation (G1) Eucalyptus plantations at 0-20 cm soil depth (p<0.05). Available phosphorus, available potassium, and organic matter levels were significantly lower in G2 and G3 than in MP at a 0-20 cm soil depth (p<0.05). The pH and bulk density were significantly lower in G2 and G3 than in MP at 0-20, 20-40, and 40-60 cm soil depths (p<0.05). However, stable isotope 15N abundance was significantly higher in G2 and G3 than in G1 at 0-20 and 20-40 cm soil depths (p<0.05). TP was defined as MP<G1<G2<G3 at the 20-40 and 40-60 cm soil depths (p<0.05). From the above results, the conversion of Masson pine forest to Eucalyptus plantations and successive planting decreased soil fertility. These findings highlight the advantages of Masson pines for Eucalyptus plantations and successive planting in improving soil fertility and production by mediating the relationships between soil physicochemical properties. This study provides a theoretical reference for the sustainable management of Masson pine forest conversion into multi-generation Eucalyptus plantations.

The land-use conversion of Masson pine forests to tea fields is extensively practiced across subtropical China, primarily driven by its economic benefit. However, the effects of this conversion on soil fungal communities and functional guilds are poorly understood. Herein, a field experiment was conducted in a Masson pine forest (F), a 5-year-old tea plantation without (FT-CK) fertilization or with (FT-N), and a 30-year-old tea plantation (FT-O) to assess the impact of Masson pine forest-to-tea conversion on soil fungal abundance, community structure, and functional guilds by using qPCR and high-throughput sequencing. Compared to F, fungal abundance significantly decreased by 95%, 68%, and 79% in FT-CK, FT-N, and FT-O, respectively, probably caused by the decreased total nitrogen content and habitat disruption. Fungal alpha diversity significantly increased in FT-N and FT-O compared to FT-CK. FT-O presented the highest percentages of Mortierella among treatments, which favours soil organic carbon accumulation. FUNGuild-based predictions showed that FT-CK and FT-N had higher relative abundances of plant pathogens than F and FT-O. FT-O presented the highest percentages of litter and soil saprotrophs but exhibited the lowest percentages of ectomycorrhizal fungi among treatments, likely driven by increased soil organic carbon, total nitrogen, and total phosphorus content. Our findings demonstrate that Masson pine forest-to-tea conversion significantly degrades soil fungal community and function, highlighting the urgent need for soil management strategies (e.g., organic amendments) to enhance soil health in tea agroecosystems.