我们经过近4年的辛苦工作，使用3个大豆品种，在我国四个大豆生产区，研究了大豆根瘤菌的生物地理学分布，高效大豆根瘤菌菌株的筛选，并开展了田间接种根瘤菌的应用实践。这项工作的结果于2018年5月2日在线发表在应用微生物学杂志（Journal of Applied Microbiology）上。

Rhizobial biogeography and inoculation application to soybean in four regions across China.

Yang SH, Chen WH, Wang ET, Chen WF, Yan J, Han XZ, Tian CF, Sui XH, Singh RP, Jiang GM, Chen WX.

J Appl Microbiol. 2018 May 2. doi: 10.1111/jam.13897. [Epub ahead of print] PMID: 29719942

• 论文发现：四个大豆生产区（黑龙江、内蒙、山东、海南）优势的大豆根瘤菌为费氏中华根瘤菌（Sinorhizobium fredii = Ensifer fredii）和埃氏慢生根瘤菌（Bradyrhizobium elkanii）。土壤内的可利用铁含量和土壤pH值决定着这两个物种的分布；铁含量高，酸性土壤内，以B. elkanii为优势的物种；而铁含量低，碱性土壤内，以S. fredii为优势物种。在不同的大豆生产区，选用大豆的根瘤菌，必须考虑土壤条件，特别是土壤铁含量和pH值，以选择合适的物种。内蒙古通辽和山东济宁以S. fredii为绝对优势菌，没有发现Bradyrhizobium属的物种存在；而黑龙江五大连池、山东临沂、海南，则以B. elkanii为优势种。山东泰安，则两个属的物种都存在。

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Combination of phylogenetic tree and rhizobial genospecies richness matrix.

The rpoB phylogenetic tree was constructed using JC69 model and 1000 bootstrap. Data of rhizobial genospecies richness were from Supplementary Table S5 and Table S6 online. Boldfaced strains were newly isolated from soybean nodules sampled from greenhouse or from field and their accession numbers for rpoB gene in GenBank were included in parentheses. Bar, 10% estimated phylogenetic divergence. Scale, corresponding to the numbers of rhizobial genospecies.

论文还比较了的温室条件和大田条件下的大豆根瘤菌物种多样性，发现两者没有显著差别。因此，在室内，通过土壤捕捉的方法获得的根瘤菌，可以代表大豆条件下土壤中根瘤菌的物种多样性。

• 研究发现，大豆品种对大豆根瘤菌的物种多样性和分布影响不显著。

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• 图2. Rhizobial ratio influenced by different factors.

• The coefficient of determination (R²) of each factor was estimated. Significance of R² (P value) was assessed by the constrained analysis of principal coordinates. The width of each arrow is proportional to the strength of the relationship between rhizobial ratio and different factors. (A) Rhizobial ratio, (B) Rhizobial inoculation, (C) Geographic regions, (D) Soybean variety, (E) Soil factor, (F) Climatic factor.

• Abbreviation for soil factor: AFe, available iron (mg kg^-1); pH, potential of hydrogen; ABo, available boron (mg kg^-1); EC, electrical conductivity (S m^-1); SCa, water-soluble calcium(mg kg^-1); OM, organic matter (g kg^-1); AP, available phosphorus (mg kg^-1). Abbreviation for climatic factor: bio2 (◦C), mean diurnal range, mean of monthly air temperature t_max – t_min; bio3, isothermality, (bio2/bio7) × 100%; bio12 (mm), annual precipitation; bio13 (mm), precipitation of wettest month; bio16 (mm), precipitation of wettest quarter. Prec5~12 (cm), mean monthly precipitation summary in May to December. Significant level: *, P = 0.05; **, P = 0.01; ***, P = 0.001.

• 研究发现，接种根瘤菌均可提高大豆的产量，变化范围为4.96%-31.67%，而单株根瘤鲜重、瘤数与大豆的产量、大豆蛋白含量呈正相关，但与大豆籽粒油的含量呈负相关。

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• 图3. The regression analysis among the root nodule number, nodule fresh weight, seed yield, seed protein and oil of soybean grown in the field.

• The width of each path arrow is proportional to the strength of the relationship. Correlation coefficient value (r) is labeled along the arrow. *, significant correlation at p < 0.05; **, significant correlation at p < 0.01. “–” before the data, negative correlation. Negative and positive correlations were shown using dashed and solid line, respectively. 

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• 该项工作对于当前我国发展大豆生产，推广选用高效的大豆根瘤菌，发挥共生固氮作用，减少氮肥的施用，提高大豆产量与品质，有重要的指导意义。

论文摘要如下：

Abstract

AIMS:

The aim of the study was to survey rhizobial biogeography and to inoculate soybean with selected rhizobia in China to enhance symbiotic nitrogen fixation (SNF).

METHODS AND RESULTS:

Biogeography, genetic diversity and phylogeny of soybean rhizobia was surveyed. Inocula were prepared and applied to soybean. Results showed that Bradyrhizobium elkanii and Ensifer fredii were widely distributed in acid and alkaline soils, respectively. Available iron was detected as the first determinant for distribution of the two rhizobia; and the soybean varieties did not greatly affect the rhizobial compatibility. Geographic latitude and precipitation in June were the main geographic and climatic factors affecting the rhizobial distribution. Inoculation with selected rhizobia increased the nodule number, fresh weight, occupation ratio, seed protein content and soybean yields.

CONCLUSIONS:

Selection and application of effective soybean rhizobia across China according to biogeography were clarified to promote the SNF, thereby improving soybean yield.

SIGNIFICANCE AND IMPACT OF THE STUDY:

Rhizobial diversity and biogeography were evaluated systematically in six sites across China. Available iron and soil pH are found to be the most important determinants for the distribution of soybean rhizobia. Inoculation to soybean enhances SNF, positively correlating to the increase of soybean yield and seed protein content. This article is protected by copyright. All rights reserved.

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