黄河三角洲5个耐盐树种苗木根系形态结构特征

对黄河三角洲盐渍土上所育的2 a生白蜡（Fraxinnus chinensis Roxb）、白榆（Ulmus pumila Linn.）、五角枫（Acer truncatum Bunge）、美国竹柳（Salix americana Linn.）和臭椿（Ailanthus altissima Swingle）5个树种苗木根系的长度、连接数量、表面积、体积、分形维数及序级等根系形态特征进行了研究分析。结果表明，5个树种苗木根系在其连接数量、长度、表面积和分形维数4个结构指标上均表现为白蜡 > 白榆 > 五角枫 > 美国竹柳 > 臭椿；在根系连接数量、长度两个结构指标上表现出良好的一致性，即细根（d≤5 mm）数量、长度占据各自总根系的主体，细根是这5个树种吸收养分的主体；5个树种苗木根系的第1～3序级根系长度之和与1～4序级根系的连接数之和均分别占据各序级根系总长度与总连接数的70%以上和80%以上。白蜡和白榆0～4序级、五角枫0～3序级、美国竹柳和臭椿0～2序级是根系的主体。臭椿、美国竹柳两个树种的根系粗壮，特别是大径级（>5 mm）根系的表面积和体积占其本身的主体。综合根系的结构指标及序级分析结果，5个树种的根系发达程度和分生能力由强到弱的排序为:白蜡 > 白榆 > 五角枫 > 美国竹柳 > 臭椿；白蜡和白榆两个树种的苗木根系数量多且有相对较高的根系序级，其侧根发达，表现出相对较强的根系分枝能力，能更好地吸收和利用土壤中的水分和养分。

Characteristics of Root Morphology of Five Salt Tolerance Species of Seedlings in Yellow River Delta Area

Five species of tree seedling planted for 2 years including Fraxinnus chinensis Roxb, Ulmus pumila Linn.,Acer truncatum Bunge,Salix americana Linn.,Ailanthus altissima Swingle root morphological characteristics for root length, root quantity, root surface area, root volume, root fractal dimension and root order were analyzed. The result showed that root joint number, root length, root surface area, root tip length and root fractal dimension all demonstrated the same comparative sequence: Fraxinnus chinensis Roxb > Ulmus pumila Linn. > Acer truncatum Bunge > Salix americana Linn. > Ailanthus altissima Swingle. Root quantity and root length of five species of seedling were consistent with each other, slim root(d≤5 mm)quantity and slim root length were the largest proportion of the total root system, slim root carried on the main uptaked function. Sum of root length of 1~3 root order for five species of seedlings accounted for more than 70 percent of each species total root length; sum of root joint number of 1~4 root order for five species of seedlings accounted for more than 80 percent of each species total root joint number. Roots of 1~4 root order of Fraxinnus chinensis Roxb and Ulmus pumila Linn. were the main proportion of total root system of each species; roots of 0~2 root order of Salix americana Linn. and Ailanthus altissima Swingle were the main proportion of total root system of each species. Roots of Salix americana Linn. and Ailanthus altissima Swingle were strong, especially the wide root(d>5 mm) surface and volume were the large proportion. According to the root system structure parameter and root order analysis result, five species of seedling roots strong degree and generative ability sequences were in the sequence of Fraxinnus chinensis Roxb > Ulmus pumila Linn. > Acer truncatum Bunge > Salix americana Linn. > Ailanthus altissima Swingle, Fraxinnus chinensis Roxb and Ulmus pumila Linn. Seedling root quantities were large, their root orders were high, their lateral roots were prosperous and generative, uptaked and utilization for water and mineral elements from soil of the lateral root were more efficient.