Cadmium (Cd) stress is becoming an increasing menace for plants, inducing a series of negative effect. Silicon (Si) plays an important role in mitigating Cd stress in plants. Here, we conducted a one-year experiment with three kinds of tree species seedlings (Schima superba, Chinese sweetgum, Chinese fir) and five levels of Cd treatments (0 mg·kg⁻¹, 6 mg kg⁻¹, 12 mg kg⁻¹, 24 mg kg⁻¹, 36 mg kg⁻¹) with or without 1 g kg⁻¹ Si addition to investigate the mitigation effect of Si on woody plants. The results in this study showed that Cd stress triggered morphological and physiological changes, inhibiting the growth of the three kinds of tree species seedlings. Low concentrations of Cd treatment stimulated the biomass production of Schima superba and Chinese sweetgum seedlings, whereas the biomass production of Chinese fir was not stimulated by Cd treatment. The stimulatory effects were also observed in the antioxidant enzyme (SOD, POD, CAT) activities of the three kinds of seedlings. The MDA contents decreased with the rise of Cd treatments. Soil pH decreased under Cd stress. BCF values of different fractions were observed to increase with the rise of Cd treatments, except for the leaf BCF value of Chinese sweetgum. The root−to−stem TF values of all increased compared with the control, while the root-to-leaf TF values were observed to decrease. Si addition enhanced the growth of the three kinds of tree species seedlings, inducing the increase of heights, ground diameter, leaf morphological parameters, biomass production, the content of chlorophyll and the activities of antioxidant enzymes. Treatment with Si significantly decreased the Cd concentration in different fractions of the three kinds of seedlings. Soil pH increased after treatment with Si. The BCF values for Si-treated plants were all observed to be lower than the non-Si-treated ones. However, the addition Si did not affect the root-to-stem and root-to-leaf TF values in the three kinds of seedlings.

The cultivation of Cunninghamia lanceolata (Lamb.) Hook. (Chinese fir) plays a crucial role in enhancing ecological security through water resource preservation and carbon sequestration in China. The biotic and abiotic environmental conditions vary across different stages of plantation, thereby influencing soil nutrient levels and microbial dynamics. However, the interconnection between the soil nutrient cycle and microbial communities within Chinese fir plantations throughout their entire life cycle remains inadequately understood. In this study, conducted across various management stages of Chinese fir plantations in China (including the juvenile stage, first thinning stage, second thinning stage, mature stage, and over-mature stage), we examined the associations among soil organic carbon, soil physicochemical properties, soil enzyme activities, and soil microbial dynamics. Our results revealed that forest management practices significantly modify soil physicochemical properties and enzyme activities across all management stages. Specifically, the concentrations of total soil carbon, soil organic carbon, and soil microbial biomass carbon were notably higher in the over-mature stage compared to other management stages. At the genus level, the five highest contributors belonged to Subgroup2, AD3, Xanthobacteraceae, Elsterales, and Acidobacteriales for the bacterial community. For the fungal community at the genus level, the five highest contributors belonged to Ascomycota, Serendipita, Saitozyma, Mortieralla, and Venturiales. Moreover, anthropogenic thinning activities during the management phase substantially altered both stand and soil environments, as well as the structural characteristics of soil microbial communities. Soil cellulase, soil electrical conductivity (EC), and soil available phosphorus (AP) emerged as key factors influencing the relative abundance of major fungal communities, whereas soil total nitrogen, EC, and AP were identified as critical factors affecting the relative abundance of major bacterial phyla. More microbiological groups increased significantly in the juvenile stage and over-mature stage. Our findings elucidate the intricate relationships between the soil nutrient cycle and soil microbiological dynamics across various forest management stages within Chinese fir plantations.