薇甘菊根际可培养固氮菌和氨化细菌的分离鉴定与促生作用

Isolation, identification and growth-promoting effects of culturable nitrogen-fixing bacteria and ammonifying bacteria in rhizosphere soil of Mikania micrantha

摘要:

【目的】固氮菌和氨化细菌是氮循环产生生物有效氮的关键起始环节，直接影响了外来入侵植物的生长速度和扩散进程。然而，关于典型入侵植物薇甘菊根际可培养固氮菌和氨化细菌的研究尚未见报道，这在很大程度上制约了我们对薇甘菊根际高效的氮素转化机制的深刻理解。【方法】采用传统平板涂布培养法对野外采集的薇甘菊根际土壤中的可培养固氮菌和氨化细菌进行了分离鉴定，并进行了接种验证实验。【结果】结果表明，入侵植物薇甘菊根际土壤中的固氮菌和氨化细菌的菌群密度显著高于两个本地伴生植物(火炭母和鸡屎藤)，其固氮效率及有机氮矿化效率也优于2个本地种；系统发育分析表明：薇甘菊根际的固氮菌菌株归类于5个属，分别为伯克霍尔德氏菌属(Burkholderia)、肠杆菌属(Enterobacter)、植物杆菌属(Phytobacter)、新肠杆菌属(Kosakonia)和根瘤菌属(Rhizobium)；氨化细菌归类于7个属，分别为沙雷氏菌属(Serratia)、不动杆菌属(Acinetobacter)、假单胞菌属(Pseudomonas)、博德特氏菌属(Bordetella)、寡养单胞菌属(Stenotrophomonas)、苍白杆菌属(Ochrobactrum)和金黄杆菌属(Chryseobacterium)；其中伯克霍尔德氏菌属与根瘤菌属是薇甘菊根际的优势固氮菌，沙雷氏菌属是薇甘菊根际的优势氨化细菌。此外，温室盆栽接种试验表明薇甘菊根际土壤的可培养固氮菌和氨化细菌对其幼苗生长具有显著的促进效应，其中根瘤菌属菌株YHAzMm-21和苍白杆菌属菌株YHAmMm-14的促生效果最佳，有望开发为微生物菌肥或工程微生物。【结论】薇甘菊根际可培养固氮菌和氨化细菌的菌群密度及其转化效率均优于本地种，并能促进自身生长。该研究明确了薇甘菊根际可培养菌群在氮循环中的贡献，并为筛选高效氮循环功能菌株提供了理想材料。

关键词:薇甘菊;可培养微生物;固氮菌;氨化细菌;促生作用

Abstract:

[Objective] Nitrogen-fixing bacteria and ammonifying bacteria are the key initial links of nitrogen cycle to produce bioavailable nitrogen, which directly affect the growth and spread of invasive alien plants. However, the culturable nitrogen-fixing bacteria and ammonifying bacteria in the rhizosphere of typical invasive plant Mikania micrantha H.B.K. have been rarely reported, which restricts our understanding of the efficient nitrogen transformation mechanism therein. [Methods] The culturable nitrogen-fixing bacteria and ammonifying bacteria in the rhizosphere soil of M.micrantha were isolated and purified by traditional culture method, and the inoculation experiment was carried out for verification. [Results] The density and nitrogen transformation rate of nitrogen-fixing bacteria and ammonifying bacteria and their nitrogen fixation efficiency and organic nitrogen mineralization efficiency were all higher than those of two co-occurring native competitors, Persicaria chinensis and Paederia scandens. Phylogenetic tree indicated that the nitrogen-fixing bacterial strains in the rhizosphere of M.micrantha were classified into five genera, including Burkholderia, Enterobacter, Phytobacter, Kosakonia and Rhizobium, and ammonifying bacterial strains fell into seven genera, including Serratia, Acinetobacter, Pseudomonas, Bordetella, Stenotrophomonas, Ochrobactrum and Chryseobacterium. Both Burkholderia and Rhizobium of the nitrogen-fixing bacteria and Serratia of the ammonifying bacteria were the dominant functional bacteria of M.micrantha. The greenhouse pot experiments of inoculation with the culturable functional strains demonstrated that the two groups of bacteria significantly promoted the growth of M.micrantha seedlings. Amongst them Rhizobium YHAzMm-21 of nitrogen-fixing bacteria and Ochrobactrum YHAmMm-14 of ammonifying bacteria had the best growth-promoting effects, which were expected to be developed into microbial fertilizers or engineering microorganisms. [Conclusion]The density and nitrogen transformation efficiency of the culturable nitrogen-fixing bacteria and ammonifying bacteria in the rhizosphere soil of M.micrantha outweighed those of the native species, which promoted the plant growth. These results clarified the contribution of the culturable flora in the rhizosphere soil ofM.micrantha to nitrogen cycle, and provided an ideal material for screening functional strains with high nitrogen cycle rates.

Key words:Mikania micrantha;culturable microorganisms;nitrogen-fixing bacteria;ammonifying bacteria;growth-promoting effects