栽植密度对毛白杨林地土壤垂直方向养分的影响

  目的  研究栽植密度对毛白杨Populus tomentosa林地土壤养分的影响。  方法  在3种不同栽植密度行距×株距分别为2 m×2 m（T₁）、4 m×3 m（T₂）和4 m×5 m（T₃）]下，对10年生毛白杨速生丰产林试验地0~5、5~10、10~20、20~40、40~60和60~100 cm共6个土层的有机质、碱解氮、有效磷和速效钾质量分数进行了分析。栽植密度对土壤养分的影响用单因素分析法，数据间的多重比较用Ducan法。  结果  0~20 cm土层有机质、碱解氮、有效磷和速效钾所占比例分别为69%、79%、71%和74%；不同栽植密度下土壤养分质量分数不一致:T₂栽植密度下有机质在0~5 cm处最高，为15.44 g·kg-1，显著高于T₁，在5~20 cm土层处3栽密度间有机质差异显著（P < 0.05），大小依次为T₃、T₂、T₁，在20~100 cm土层处T₁显著低于T₃和T₂（P < 0.05）；碱解氮在T₂下为14.5~142.7 mg·kg-1，高于T₁和T₃（除5~10 cm）；有效磷为1.3~12.4 mg·kg-1，5~40 cm土层T₂显著高于T₁和T₃（P < 0.05），40~100 cm土层大小依次为T₃、T₂、T₁；栽植密度对速效钾无显著影响（P>0.05）。  结论  10年生毛白杨林地土壤养分富集在0~20 cm土层，栽植密度为2 m（行距）×2 m（株距）的养分低于栽植密度为4 m×3 m和4 m×5 m，养分质量分数随栽植密度和不同土层的变化而变化。

Planting densities and vertical soil nutrients in a Populus tomentosa stand

  Objective  To explore the effects of planting densities on soil nutrients of different soil layers for a Populus tomentosa plantation.  Method  10-year-old S86 clones were used to study the soil nutrient characteristics with three planting densities (T₁:2 m×2 m; T₂:4 m×3 m; and T₃:4 m×5 m) for six soil layers (0-5, 5-10, 10-20, 20-40, 40-60, and 60-100 cm). In mid-October 2016, soil samples were collected, and the contents of carbon (C), available nitrogen (N), available phosphorus (P), and available potassium (K) were determined and in total there were 3 treatments with 3 replicates, then one-way ANOVA and Duncan's multiple comparison tests were used to determine significant differences.  Result  The proportions of nutrients in the 0-20 cm layer compared to the 0-100 cm layer were:C(69%), N(79%), P(71%), and K (74%). The content of soil nutrients varied for the three planting densities. The highest C content found in T₂ (15.44 g·kg-1 in the 0-5 cm layer) was significantly higher (P < 0.05) than T₁; the C content in the 5-20 cm layer was significantly different (P < 0.05) than other densities in the order of T₃ > T₂ > T₁; and in the 40-100 cm layer, the T₁ content was significantly lower (P < 0.05) than other densities. The N content in T₂ was 14.5-142.7 mg·kg-1. The P content was 1.3-12.4 mg·kg-1 with the content of T₂ being significantly higher (P < 0.05) than other layers from 5-40 cm; however, in the 40-100 cm layers the content was T₃ > T₂ > T₁. Planting density, though, had no significant effect on K content (P>0.05).  Conclusion  Nutrient content varied according to planting density and soil layers with the soil nutrient content of 10-year-old P. tomentosa clone S86 gathered in the 0-20 cm layer for the 2 m×2 m density having a lower nutrient content than the 4 m×3 m and 4 m×5 m densities.