Abstract: As a plant growth regulator,fulvic acid (FA) can promote plant growth. The purpose of this study is to investigate the effect of FA on rhizobia and Medicago sativa seedling growth,and endogenous host colonization of rhizobia. The three rhizobia strains labeled with cyan fluorescent protein (Rhizobium LH3436f,Rhizobium GN5f and Ensifer meliloti 12531f) were used as materials. The concentrations of FA suitable for the growth of each rhizobia strain were screened,and added into rhizobia solutions for inoculation. The effects of FA on rhizobia nodulation,the growth of M. sativa seedlings and the ability of endogenous host colonization of rhizobia were determined. Our results showed that inoculating rhizobia solutions added with proper concentrations of FA significantly contributed to the invasion and colonization of labeled rhizobia in M. sativa seedlings root. After inoculated with 12531f solution containing 0.02% FA,the endogenous colonization quantity of 12531f in roots of M. sativa reached 11.18 times that of the single inoculation (without FA) (P<0.05). By inoculating rhizobia solutions added with proper concentrations of FA,nodulation and growth of M. sativa were significantly increased, and M. sativa inoculated with 3436f added with 0.01% FA gave the best results. By inoculating rhizobia solutions added with proper concentrations of FA,the chlorophyll content of M. sativa significantly increased,and the best treatment was M. sativa inoculated with gn5f added with 0.02% FA,which presented the higher chlorophyll content (111.41%) than that of WCK (P<0.05). Therefore,FA can promote the colonization of rhizobia in M. sativa seedlings,and FA together with rhizobia can synergistically promote the growth of M. sativa seedlings.

Key words: Fulvic acid, Rhizobium, M. sativa, Endogenous host colonization, Growth

摘要： 黄腐酸（Fulvic acid，FA）是一种植物生长调节剂，可促进植物生长。为探索FA对根瘤菌生长、菌株内生定殖及幼苗生长的影响，本试验以3株青色荧光蛋白标记根瘤菌株Rhizobium LH3436f（3436f）、Rhizobium GN5f（gn5f）和Ensifer meliloti 12531f（12531f）为材料，筛选出有利于各标记根瘤菌生长的FA浓度，添加到根瘤菌液中并接种于苜蓿幼苗根系，检测根瘤菌结瘤、苜蓿幼苗生长和菌株内生定殖情况。结果表明：添加适宜浓度FA可显著促进标记根瘤菌侵染根系和在苜蓿体内定殖，12531f根瘤菌添加0.02% FA后接种苜蓿，其在根中的内生定殖数量达到单独接种的11.18倍，差异显著（P<0.05）；根瘤菌添加FA接种可明显促进苜蓿结瘤和生长，效果最佳的是3436f添加0.01% FA接种；根瘤菌添加FA接种也使苜蓿叶绿素含量显著提高，gn5f添加0.02% FA时苜蓿叶片叶绿素含量最高，显著高出WCK 111.41%（P<0.05）。因此，FA可促进根瘤菌在苜蓿幼苗内的定殖，二者可协同促进苜蓿幼苗生长。

关键词: 黄腐酸, 根瘤菌, 紫花苜蓿, 内生定殖, 生长