毛白杨VA菌根与外生菌根关系的研究

定期从毛白杨扦插育苗地挖取根样，并从中原地区的毛白杨人工林地采集细根（直径小于２ｍｍ）根样，观察统计ＶＡ菌根、外生菌根、混合菌根以及未受菌根菌侵染的１ｃｍ长根段的百分比。结果表明，在苗木的菌根侵染初期，ＶＡ菌根菌的侵染势较强，但优势很快被外生菌根菌取代，两种菌根菌间的负交互作用随苗龄的增加而不断增强。造林地种类和土壤的ｐＨ值对毛白杨两种菌根间的负交互作用关系有制约作用。在强碱性砂土地上，ＶＡ菌根的

STUDY OF NEGATIVE ASSOCIATIONS AMONG VAAND ECTOMYCORRHIZAE OF POPULUS TOMENTOSA

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.