Effects of Successive Planting of Eucalyptus on Soil Physicochemical Properties 1-3 Generations after Converting Masson Pine Forests into Eucalyptus Plantations

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 N-15 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.