白刺花根瘤中分离细菌的物种多样性及其促生效应

Species diversity and plant growth-promoting effects of bacteria isolated from the root nodules of Sophora davidii

摘要:

【目的】 除根瘤菌外，豆科植物的根瘤中还广泛存在大量的非根瘤菌。与植物其他组织中的内生细菌相比，对根瘤中非根瘤菌的物种多样性尚缺乏系统研究，它们存在的意义及其生态学作用更需深入研究和探讨。【方法】 以陕北黄土丘陵沟壑区野生豆科固氮灌木白刺花为研究对象，通过传统培养法对白刺花根瘤中根瘤菌和非根瘤菌的物种多样性开展全面系统的研究，评价菌株的促生特性，并验证其对小麦的促生效果。【结果】 从陕北6个不同县区的白刺花根瘤中共筛选获得320株内生细菌，16S rRNA基因系统发育分析将它们鉴定为4门7纲17目35科55属，其中假单胞菌属(Pseudomonas, 18.44%)、芽孢杆菌属(Bacillus, 17.81%)和中慢生根瘤菌属(Mesorhizobium, 11.56%)是白刺花根瘤中的优势菌属。回接试验表明，中慢生根瘤菌属菌株和苍白杆菌属菌株HL-2均能与宿主植物白刺花共生形成根瘤。对宝塔区的192株白刺花根瘤内生细菌进行促生特性研究，结果显示115株细菌具有固氮能力，20株细菌具有较好的溶磷能力，78株具有分泌吲哚乙酸(indole-3-acetic acid, IAA)的能力，18株分泌铁载体。从中选取了4株优良菌株，通过单菌及多菌混合接种，测定它们对盆栽种植的小麦农艺的促生作用，结果表明处理组HIJ对小麦的株高和鲜重分别提高了49.65%和140.00%，处理组HK对小麦的根长提高了45.84%，处理组IK对小麦幼苗的叶绿素含量提高了25.48%。【结论】 白刺花根瘤中具有物种多样的非根瘤菌。本研究结果对进一步探明此类微生物资源在自然生态系统中的作用和丰富内生细菌资源库有重要的科学意义，同时也为它们在陕北干旱区生态恢复中的应用提供理论依据。

Abstract:

[Objective] There are numerous non-rhizobia in addition to rhizobia in the root nodules of leguminous plants. Despite the extensive studies about the endophytic bacteria in other plant tissues, little attention has been paid to the species diversity of non-rhizobia in root nodules. Therefore, further research is needed to explore the significance and ecological roles of non-rhizobia. [Methods] The root nodules of wild Sophora davidii (Franch.) Skeels, a leguminous nitrogen-fixing shrub growing in the hilly-gully loess region of northern Shaanxi, were collected. The species diversity of rhizobia and non-rhizobia in the root nodules of S. davidii was systematically studied by the conventional culture method. The plant growth-promoting effects of the strains were evaluated and their growth-promoting effects on wheat seedlings were verified. [Results] A total of 320 strains of endophytic bacteria were isolated from the root nodules of S. davidii in six counties/districts in northern Shaanxi. The phylogenetic analysis based on the 16S rRNA gene sequences identified the strains into 55 genera, 35 families, 17 orders, 17 classes of 4 phyla. Pseudomonas (18.44%), Bacillus (17.81%), and Mesorhizobium (11.56%) were the dominant genera. The results of re-inoculation experiments showed that Mesorhizobium sp. and Ochrobactrum sp. HL-2 formed root nodules with the host plant. Furthermore, the plant growth-promoting characteristics of 192 strains isolated Baota District were studied. The results showed that 115, 20, 78, and 18 strains possessed the abilities of fixing nitrogen, solubilizing phosphorus, producing indole-3-acetic acid (IAA), and secreting siderophores, respectively. Four elite strains were selected and inoculated alone or in combination into the wheat seedlings in pots, and their growth-promoting effects on the agronomic traits of wheat seedlings were evaluated. The results indicated that the treatment HIJ increased the plant height and fresh weight of wheat seedlings by 49.65% and 140.00% respectively. The treatments HK and IK increased the root length and chlorophyll content by 45.84% and 25.48%, respectively. [Conclusion] There are diverse non-rhizobia in the root nodules of S. davidii. The results of this study have great scientific significance for exploring the role of such microbial resources in natural ecosystems and enriching the resource pool of endophytic bacteria. Additionally, the results provide a theoretical basis for the application of these strains in ecological restoration in the arid region of northern Shaanxi.