Abstract: Roots and fine roots(<2mm diameter)were sampled periodically from P.tomentosa cutting plantlings grown in cuttingbed, and from plantations of P. tomentosa growing in Central Plains of China.Percentages of VA-mycorrhizal,ectomycorrhizal, dual colonized, and non-mycorrhizal root lengths were determined.The results showed that in primary infections of cutting plantings by mycorrhizal fungi,VA mycorrhizae predominantly occurred in the root system but were then rapidly supplanted by ectomycorrhizae.The negative interactions among VA -and ectomycorrhizal fungi strengthened with ageing of the cutting planttings. History of the afforested area and soil pH-value have an instrictive effect on the negative interactions among the mycorrhizal fungi. On the alkali sand site,the percentage of VA-mycorrhizal root lengths was much more than that on the neutral forest soil site, there was a significantly difference between them.

Key words: Populus tomemtosa, Cutting planttings, VA-and ectomycorrhizae, Negative interaction