Objective  Parashorea chinensis is a tropical rainforest species and a national first class endangered tree species, and the artificial cultivation is an important way to expand its population size. This study analyzed the soil physicochemical properties, soil microbial biomass carbon (SMBC), nitrogen (SMBN) and soil nutrient contents with their stoichiometric characteristics in different stands and soil layers of the young P. chinensis plantation, providing referable evidence for the optimal selection of mixed tree species and soil management.

  Method  The standard sites were set up in P. chinensis artificial pure and mixed plantations and the soil samples of different soil layers were collected by diagonal method. The soil pH value, organic matter and nutrient content, SMBC and SMBN content were measured, further it was discussed about the effects of different stands and soil layers on the contents of SMBC and SMBN and the soil quality by ecological stoichiometry and principal component analysis.

  Result  (1) The vertical distribution characteristics of SMBC, SMBN and soil nutrient content decreased with the deepening of soil depth, different stand types had no obvious effect on its vertical distribution. (2) The average soil C∶N∶P of P. chinensis plantation was 35∶2∶1, average SMBC∶SMBN was 8∶1. The composition of different tree species significantly affected the changes of soil nutrients, SMBC, SMBN and their stoichiometric ratio, the mixed plantation of P. chinensis and Eucalyptus grandis × E. urophylla could improve the soil microbial activity, soil texture and microenvironment. (3) Correlation and principal component analysis revealed that: the soil microorganism in Parashorea chinensis plantation could maintain a certain internal stability through self-regulation, and SMBC, SMBN might be used as early biological indicators of changes in soil nutrient reserves and C, N sources. The mixed P. chinensis and Eucalyptus grandis × E. urophylla plantation had the most significant effect on soil microecological function, quality and fertility, which suggested that this stand type could be more favorable for the growth of soil microorganism and the development of soil nutrients in young Parashorea chinensis forest land.

  Conclusion  The contents of SMBC, SMBN and nutrients with their stoichiometric characteristics of P. chinensis plantation show obvious surface accumulation effect, and the composition of tree species has no obvious effect on its vertical distribution. Compared with the pure plantation, the P. chinensis mixed plantation has more significant effect on soil microbial environment and soil quality. Particularly, the mixed plantation of P. chinensis and Eucalyptus grandis × E. urophylla better improve the function of microorganism and soil structure as well as the activation of nutrients, indicating that this mixed pattern can be selected as the appropriate choice for young P. chinensis plantation and one of the suitable transformation ways for pure Eucalyptus plantation.