关键词: 土壤化学计量, 养分平衡, 种间关系, 混交距离

Abstract: Two-year-old seedlings of Ulmus pumilaL. were planted in sandy soils in the downstream region of Yongding River, to study their shoot growth and root development after extra-deep-planting. Long root and commonroot seedlings were planted at 1 m depth of soil (designated as LD and CD, respectively), and commonroot seedlings were conventionally planted at 0.3 m depth of soil as control (CC). In the second year after planting, soil water contents were mea-sured from surface to 1 m depth at 0.2 m intervals. Shoot and root growth parameters were mea sured  at the end of the experiment. Results showed that: (1) Soil water contents in deep layer (below 60 cm) were relatively stable and generally higher than the shallow layer (0-40 cm) throughout the growing season. (2) Shoot growth was significantly different among the treatments, with LD being the best and followed by CD and CC. (3) Root development was generally better in LD treatment than the other two treatments. (4) The distribution of roots were different among treatments, whereas whole root and fine roots at different soil layers exhibited similar distribution in each treatment. Roots were intensively developed in 0-0.2 m for the LD, in 0-0.2 and below 0.8 m for the CD, and in 0-0.4 m for the CC. No roots were found below 0.8 m in CC treatment. The growth of LD seedlings was better than CD and CC ones. Root distribution pattern of LD corresponded with the water distribution in different soil layers, which may be contributed to the water absorption of seedlings. Therefore, we recommend long-root seedlings with extra deepplanting for afforestation in arid sandy lands. Considering the low cost of transportation and appropriate root distribution, commonroot seedlings can also be recommended for afforestation.

Key words: mixed distance, nutrient balance., soil stoichiometry, interspecific relationship