覆土厚度对城市园林植物生长的影响分析

城市绿地地下空间开发对解决城市建设与绿化用地之间的矛盾至关重要，覆土厚度作为其重要参数指标，对园林植物生长和工程建设成本具有重要的影响。通过不同覆土厚度(0.5、1.0、1.5m)处理与地面对照下北京城市5种常见园林植物地上部及其根系生长的多年监测与分析发现以下几方面。1)与地面对照相比，0.5m覆土处理与1.0m覆土处理明显限制了速生树种洋白蜡的地上部生长；但各覆土处理未明显限制生长速率较慢的油松和紫薇的生长；而0.5m覆土处理明显限制了灌木类(大叶黄杨与金银木)的地上部生长。2)植物生长5年后，所有覆土处理中的植物根系均已到达种植池底部，且0.5m覆土处理的粗根分布密度明显高过其他处理，表现出一定程度的根系相互压迫与横向生长现象。乔木根系生长随着覆土年限的推移将会受到不利影响。

On the Influence of Soil Thickness on the Growth of Urban Garden Plants

The underground space development of urban green space is crucial to solve the contradiction between urban construction and green land. As an important parameter indicator, soil thickness has an important influence on the growth of landscape plants and the construction cost. Through years of monitoring and analysis of aboveground and root growth of five common garden plants in Beijing under different soil thickness (0.5m, 1.0m, and 1.5m) and ground control, it was found that: 1) Compared with the ground control, the 0.5m soil thickness treatment and the 1.0m soil thickness treatment significantly restricted the aboveground growth of the Fraxinus pennsylvanica, a fast-growing species; but soil thickness treatments did not significantly restrict the growth of Pinus tabuliformis and Lagerstroemia indica, the species with slower growth rate; moreover, the 0.5m soil thickness treatment has obviously limited the aboveground growth of shrubs such as Buxus megistophylla and Lonicera maackii. 2) After 5 years of plant growth, the roots of plants in all treatments and ground control reached the bottom of the planting pond. The distribution density of coarse roots in the 0.5m soil thickness treatment is significantly higher than that of other treatments, showing a certain degree of root mutual compression and lateral growth. The root growth of trees will be affected as the years.