Changes of Soil Chemical Properties after Pure Masson's Pine Plantations Transferred into Mixed Conifer-Hardwood Stands

One-year old seedlings of six broad-leaved tree species,Michelia macclurei,Castanopsis fissa,Castanopsis sclerophylla,Castanopsis kawakamii,Cyclobalanopsis myrsinaefolia and Castanopsis lamontii,were separately planted under 25-year-old Masson's pine plantation,and developed into different closed mixed forests after 16 years.The major chemical properties of the soils supporting the six mixed stands and the pure Masson's pine plantation were analyzed to study the response of the soils to the interplanting practice.The results showed that planting broad-leaved species(excluding Cyclobalanopsis myrsinaefolia) under Masson's pine stand significantly increased organic matter contents in the surface soils(0~20 cm).The average contents of total K,Mg,Ca, N and P in the soils beneath all the seven types of stands(including pure Masson's pine stand) were 11.41,6.64,4.33,1.45,and 0.46 g/kg,respectively,suggesting the soils holding abundant K,Mg and Ca,but lacking N and P.Establishment of mixed forests,to some extents,improved the status of N and P supplies in the soils.The contents of available N and P featuring the mixed stands were consistently greater than the single-species plantation,but reverse for available K.The average pH value of the soils under the mixed stands was 4.40 in the depth of 0~20 cm,4.61 in 20~40 cm,and 4.68 in 40~60 cm,but the pH values in the corresponding soil layers under pure stand were 4.39,4.41 and 4.42, respectively,indicating interplanting broad-leaved species decreased the acidity of the soil solutions.The practice of growing broad-leaved species(except Castanopsis sclerophylla) under Masson's pine canopy elevated percent base saturation of the soils,due to the interactive effects of decreased exchange acidity and increased basic cation concentrations.