Low pH with aluminum (Al) toxicity are the main limiting factors affecting crop production in acidic soil. Selection of legume crops with acid tolerance and nitrogen-fixation ability should be one of the effective measures to improve soil quality and promote agricultural production. The role of the rhizosphere microorganisms in this process has raised concerns among the research community. In this study, BX10 (Al-tolerant soybean) and BD2 (Al-sensitive soybean) were selected as plant materials. Acidic soil was used as growth medium. The soil layers from the outside to the inside of the root are bulk soil (BS), rhizosphere soil at two sides (SRH), rhizosphere soil after brushing (BRH) and rhizosphere soil after washing (WRH), respectively. High-throughput sequencing of 16S rDNA amplicons of the V4 region using the Illumina MiSeq platform was performed to compare the differences of structure, function and molecular genetic diversity of rhizosphere bacterial community of different genotypes of soybean. The results showed that there was no significant difference in alpha diversity and beta diversity in rhizosphere bacterial community among the treatments. PCA and PCoA analysis showed that BRH and WRH had similar species composition, while BS and SRH also had similar species composition, which indicated that plant mainly affected the rhizosphere bacterial community on sampling compartments BRH and WRH. The composition and abundance of rhizosphere bacterial community among the treatments were then compared at different taxonomic levels. The ternary diagram of phylum level showed that Cyanobacteria were enriched in WRH. Statistical analysis showed that the roots of Al-tolerant soybean BX10 had an enrichment effect on plant growth promoting rhizobacteria (PGPR), which included Cyanobacteria, Bacteroides, Proteobacteria and some genera and species related to the function of nitrogen fixation and aluminum tolerance. The rhizosphere bacterial community from different sampling compartments of the same genotype soybean also were selectively enriched in different PGPR. In addition, the functional prediction analysis showed that there was no significant difference in the classification and abundance of COG (clusters of orthologous groups of proteins) function among different treatments. Several COGs might be directly related to nitrogen fixation, including COG0347, COG1348, COG1433, COG2710, COG3870, COG4656, COG5420, COG5456 and COG5554. Al-sensitive soybean BD2 was more likely to be enriched in these COGs than BX10 in BRH and WRH, and the possible reason remains to be further investigated in the future.
针对酸性土壤中影响作物生产的主要限制因子(pH及其铝毒),选用耐酸铝且具有固氮能力的豆科作物是改良该类土壤、促进农业生产的有效措施之一,至于其所关联的根际微生物是否起到相应的促进作用,一直为国内外学者所关注和探究。为此,本研究以铝耐受型大豆品种基因型(BX10)和铝敏感型大豆品种基因型(BD2)为材料,以酸性红壤为生长介质,采样部位按照土层到根系的距离由远到近的顺序划分为：根外对照土(bulk soil, BS)、两侧根际土(rhizospheric soil at two sides, SRH)、刷后根际土(rhizospheric soil after brush, BRH)和冲洗后的根际土(rhizospheric soil after wash, WRH)。利用Illumina MiSeq对16S rRNA基因扩增产物的高变区V4进行高通量测序,研究了不同耐铝基因型大豆根际细菌群落的结构、功能与分子遗传多样性的差异性作用。结果表明,各处理间大豆根际细菌群落的alpha多样性无显著性差异,beta多样性差异也均不显著。PCA和PCoA分析可见BRH和WRH部位的物种组成较为一致,而BS和SRH部位具有相似的物种组成,说明植物生长主要影响根际的BRH及WRH部位的微生物,对SRH影响较小。对各分类水平物种组成和丰度进行比较,门分类水平三元图表明两个基因型大豆均在WRH部位富集蓝细菌门(Cyanobacteria)细菌;统计分析表明铝耐受型大豆(BX10)根部对于增强植物抗逆性的植物根际促生菌(plant growth promoting rhizobacteria, PGPR)有富集作用,这些富集的细菌包括蓝细菌门、拟杆菌门(Bacteroidetes)和变形菌门(Proteobacteria)等,以及部分与固氮和耐铝的功能相关的属种。另对同一个基因型大豆不同采样部位间进行比较分析,结果显示土壤不同采样部位可以选择性富集不同的PGPR物种。此外,16S rDNA的同源蛋白簇(clusters of orthologous groups of proteins, COG)功能预测分析的结果表明,多个COG包括COG0347、COG1348、COG1433、COG2710、COG3870、COG4656、COG5420、COG5456和COG5554均可能与固氮直接相关;BD2相比于BX10,结果显示在BRH和WRH部位似乎均更易富集固氮直接相关的COG,其可能的原因尚待进一步研究。.
Keywords: PGPR; acidic soil; aluminum-tolerant soybean; bacterial community; rhizosphere.