Enhancing soil functioning in Chinese fir plantations through mixed-species management by underplanting Phoebe bournei: Evidence from soil quality and litter water absorption

• Mixed management improved topsoil quality in Chinese fir plantations. • Effects were concentrated in the 0–20 cm soil layer. • Mixing enhanced water retention, nutrient availability and enzyme activity. • MDS identifies AK, TK and SUC as key soil quality indicators. • The 3:7 Chinese fir– Phoebe bournei pattern supports sustainable plantation soil management.