林分密度和立地类型对北京山区侧柏人工林根系的影响

该文采用土柱法对北京山区侧柏人工林的根系分布特征进行了调查研究.结果表明:林分密度、立地类型及其交互作用均对侧柏人工林根系产量与垂直分布有极显著的影响，并以林分密度的作用强度最大.侧柏林土壤表层的根长密度(P0.05)、根系表面积密度(P0.001)随着林分密度的增加而显著增加，但这种势态随土层加深变幅递减.直径1 mm的根系长密度所占比例、直径1 mm和1～2 mm根表面积密度所占比例以及根体积密度所占比例随林分密度的提高而显著提高的现象表明，在种内竞争前提下，侧柏林木通过提高个体细根产量而提高对土壤资源的利用强度，并获得有限的土壤资源.侧柏人工林林木根系的根长密度、根表面积密度随着立地条件的改善而显著降低，根长密度、根表面积密度在立地类型间的差异有随着土壤层次的加深而减小的趋势.阳坡薄土立地林木根长密度、根系表面积密度平均比阳坡厚土立地高20.4%和20.9%.该现象表明，在瘠薄立地上，侧柏林木通常采取提高根系吸收范围的对策获取有限的土壤资源. 

Effects of stand density and site types on root characteristics of Platycladus orientalis plantations in Beijing mountainous area

Soil coring was applied to investigate the root characteristics of Platycladus orientalis plantations in Beijing mountainous area. Results showed that the stand density, site types and their interaction affected root production and root vertical distribution of planted P. orientalis stands obviously, and stand density was the most intensive factor to influence root characteristics. The root length density (P<0.05) and root surface area density (P<0.001) in surface soil layer increased with the increase of stand density, but this trend declined with soil layer going to deeper. The phenomenon of that, the proportion of root length density in diameter of <1 mm, the root surface area density and root volume density in diameter of <1 mm and 12 mm remarkably increased with the increase of stand density, indicated that P. orientalis plantations would for age limit soil resources by increasing fine root production when intraspecific competition occurred. The root length density and root surface area density were evidently declined with the improvement of site quality. But the differences of root length density and root surface area density among sites were weakened in the deeper soil layers. In general, the root length density and root surface area density were 20.4% and 20.9% higher in the site of sun oriented aspect and shallow soil than those of the sun oriented aspect site and deep soil. This phenomenon suggests that P. orientalis plantations take wider root absorption range as their strategy to implore the limited soil resources when trees