北京平原地区不同造林树种林下土壤化学计量特征

土壤有机碳、氮和磷浓度及其比例对林木的生长发育具有重要影响，探究树种-土壤养分之间的关系，可为平原地区人工林规划和管理以及土壤肥力恢复提供科学指导。以北京市大兴区平原造林区域5种人工纯林（国槐、毛白杨、银杏、油松和榆树）为研究对象，对林下0 ~ 20 cm和20 ~ 40 cm土壤有机碳、全氮和全磷浓度，以及生态化学计量特征和相关性进行研究。结果表明：（1）在0 ~ 20 cm，树种对土壤有机碳、全氮和全磷浓度均存在显著影响（P＜0.05）；在20 ~ 40 cm，树种对土壤全氮浓度影响显著。随土层加深，各树种林下土壤有机碳、全氮和全磷总体上呈下降趋势。研究区土壤有机碳、全氮和全磷浓度均低于全国平均值，尤其以缺氮最为严重。（2）在0 ~ 20 cm，不同树种之间土壤C:N、C:P和N:P均存在显著差异。榆树林土壤C:N显著大于毛白杨林、油松林和银杏林，银杏林土壤C:P显著高于毛白杨林和榆树林，而银杏林土壤N:P显著高于国槐林和榆树林。随着土层加深，土壤C:N、C:P和N:P变化各异。土壤C:P和N:P均远低于全国土壤均值。（3）相关分析表明，土壤全氮主要影响C:N和N:P，土壤有机碳主要影响C:P。国槐林和油松林在改善土壤养分方面有较好的效果。北京市平原造林区域的氮可能是影响林木生长的主要限制性元素，建议在后期的抚育管理过程中施用适量的氮肥，为造林树种提供良好的生长环境。

Soil chemical stoichiometry characteristics under different afforestation species in plain area, Beijing

Soil organic carbon (C), nitrogen (N) and phosphorus (P) concentrations and their ratios have important impacts on tree growth and development. Exploring the relationship between tree species and soil nutrients will provide guidance for plantation planning and management and soil fertility restoration in the plains. In this study, five kinds of pure plantations (Sophora japonica, Populus tomentosa, Ginkgo biloba, Pinus tabuliformis and Ulmus pumila) in the plain afforestation area, Daxing District, Beijing, were selected to study soil organic carbon, total nitrogen, total phosphorus, their ecological stoichiometry and relationship at depths of 0-20 and 20-40 cm. The results showed that: 1) At 0-20 cm, the tree species had significant effects on the soil organic carbon, total nitrogen and total phosphorus (P<0.05), while a significant difference was just observed for the soil total nitrogen between the tree species at 20-40 cm. With the increase of the soil depth, soil organic carbon, total nitrogen and total phosphorus concentrations showed decreasing trends for all tree species. Soil organic carbon, total nitrogen and total phosphorus in the study area were lower than the average of China, and especially nitrogen shortage was the most serious. 2) At 0-20 cm, there were significant differences in soil C:N, C:P and N:P ratios. The soil C:N in Ulmus pumila plantation was significantly higher than plantations of Populus tomentosa, Pinus tabulaeformis and Ginkgo biloba. Soil C: P in Ginkgo biloba plantation was significantly higher than Populus tomentosa and Ulmus pumila. Soil N: P in Ginkgo biloba plantation was significantly higher than Populus tomentosa and Sophora japonica. With the increase of the soil depth, its C: N, C: P and N:P ratios varied differently. The C:P and N:P ratios of the soil were lower than the national average. 3) The correlation analysis showed that C: N