Effects of different density regulation intensities on soil quality in Larix principis-rupprechtii plantation

  Objective  This paper aims to explore the variation law of soil quality of Larix principis-rupprechtii plantation under different density regulation intensities, which provides a theoretical basis for rational utilization of forest land resources and sustainable management of plantation.

  Method  In this study, we analyzed 18 soil indexes including soil density, moisture content, nutrient content and enzyme activity in L. principis-rupprechtii plantation, under four different density regulation intensities (control, 2 096 tree/ha, CK; low intensity treatment, 1 850 tree/ha, LT; moderate intensity treatment, 1 402 tree/ha, MT; high intensity treatment, 1 106 tree/ha, HT) in Taiyue Mountain, Shanxi Province of northern China. And the minimum data set (MDS) of soil quality evaluation was established by combining principal component analysis (PCA) and correlation analysis. Finally the soil quality of L. principis-rupprechtii plantation was synthesized by the weighted additive index.

  Result  Compared with CK, the soil moisture of LT, MT and HT increased. In terms of the effects of density regulation on soil nutrients, the contents of C, N and P in MT were higher. In addition, soil biological properties also showed significant response to different regulation intensities, among which, soil microbial biomass carbon and nitrogen contents in MT were significantly higher than those in CK; urease and polyphenol oxidase activities were the highest in MT, peroxidase activity was the highest in LT, and sucrase activity was the highest in CK, while cellulase activities showed a downward trend with the increase of density regulation intensity. The results of PCA and correlation analysis showed that the MDS for soil quality evaluation included organic matter, moisture content, microbial biomass nitrogen, polyphenol oxidase and peroxidase. The order of soil quality of different density regulation intensity plantation was as following: MT (0.598), HT (0.510), LT (0.432), CK (0.339).

  Conclusion  Density regulation can effectively improve the soil quality of L. principis-rupprechtii plantation, and the soil quality index of medium stand density is the highest. Therefore, we recommend moderate density regulation to L. principis-rupprechtii plantation to promote soil quality.