[Background] Root system is a critical organ for plants to absorb water and nutrients.The more the number of roots and the longer the root is,the deeper and wider the distribution is,and the stronger the ability of soil consolidation of plant roots is.That is,the quantitative and structural characteristics of the root system have an important impact on the soil consolidation of plant roots.There are many open-pit coal mines in Inner Mongolia,which have caused the growing difficulties of plant roots and a large amount of surface runoff.[Methods] In Heidaigou opencast dump site of Zhunger coalfield at Erdos City of Inner Mongolia,choosing the sample plots where 3-4 years old Hedysarum laeve,Astragalus adsurgens,and Melilotus suaveolens grew well,we randomly selected 50 of each plant as the sample,and measured their ground diameters (maximum diameter,plant height and crown width).Further we chose 5 plants closest to the average value from the 50 plants as standard plants.Then we determined the root diameter class by digging whole plant,measuring root diameter with electronic Vernier caliper,and measuring root length with tape.The method of determining the represented root is to classify the root system at an interval of 0.5 mm,calculate the cumulative root number,the cumulative root length and the cumulative root surface area of each diameter class.The relatively large diameter groups were taken as their represented roots.[Results] 1) In the total number of roots,the order of their branching abilities was M.suaveolens (79) ＞ A.dadanensis (67) ＞ H.leave (52),this was related to the plant's own biological characteristics.According to the number of different lateral roots,there were lateral roots Ⅲ for 3 plants.Among them,the number of lateral roots Ⅲ was ＞ the number of lateral roots Ⅱ ＞ the number of lateral roots Ⅰ for H.leave and A.adsurgens.The percentages of number of lateral roots Ⅱ and Ⅲ were 87％ and 80％ respectively,obviously larger than the percentage of lateral roots Ⅰ at 13％ and 20％.For M.suaveolens,the number of lateral roots Ⅲ was higher than that of lateral roots Ⅰ ＞ number of lateral roots Ⅱ,and the percentage of the number of lateral roots Ⅱ and Ⅲ was 71％,significantly larger than that of lateral roots Ⅰ,28％.The results indicated that the root system of three species was mainly fine root in soil.2) Their represented root diameter classes were H.laeve 0 mm-2.5 mm,A.adsurgens and M.suaveolens 0 mm-1.5 mm,respectively.The roots of 3 plants in soil were mainly distributed with ≤ 2.5 mm.[Conclusions] The represented root diameter should be taken as the main research scope while studying biomechanical properties of root system fixing soil and resisting erosion.%以内蒙古鄂尔多斯市准格尔煤田黑岱沟露天矿排土场内3种2～4年生典型水土保持植物杨柴(Hedysarum laeve)、沙打旺(Astragalus adsurgens)和草木樨(Melilotus suaveolens)的根系为对象,通过研究根系的数量特征,确定其代表根,为进一步研究3种植物根系生物力学特性奠定基础.代表根的确定是将根系以0.5 mm为1个径级进行分级,计算每个径级组的累计根数量、累计根长和累计根表面积等,取这3个值中比例相对较大的径级组作为各自的代表根.结果表明,杨柴代表根径级为0～2.5 mm、沙打旺和草木樨代表根径级相同为0～1.5mm.表明3种植物根系在土壤中以≤2.5mm的细根分布为主;因此,在根系固土抗蚀生物力学性质的研究中,建议以3种植物的代表根径级为主要研究范围进行研究.
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