强酸环境下产胞外多糖菌株筛选及其酸土改良效应

Screening of exopolysaccharide-producing strains in a strongly acidic environment and evaluation of their amelioration effects on acidic soils

摘要:

目的 为改善强酸性土壤结构不良、肥力衰退等问题，分离具有耐酸产胞外多糖(exopolysaccharides, EPS)特性的多种微生物，构建复合菌剂，并评估其对酸性土壤结构与综合肥力的改良效应。方法 从重庆南川、云南曲靖的强酸性土壤(pH<4.5)中经初筛、复筛获得目标菌株，鉴定其拮抗性、促生性等并构建复合菌剂；采用室内土培实验探究不同菌剂处理的强酸性土壤中养分含量及团聚体组成的变化，综合评价肥力改良效果，明确团聚体形成与EPS含量的相关关系。结果 筛选获得3株具有耐酸、产EPS特性的菌株：副伯克霍尔德菌(Paraburkholderia fungorum) C3、洋葱伯克霍尔德菌(Burkholderia cepacia) A13以及小囊担子菌(Cystobasidium minutum) B14。这些菌株兼具分泌吲哚乙酸(indole-3-acetic acid, IAA)、合成铁载体以及溶磷能力。进一步将它们单独或构建成复合菌剂分别施入土壤，发现复合菌剂对土壤养分提升效果最佳，有机质、碱解氮、有效磷、速效钾含量分别提升4.51%、13.92%、4.92%、3.71%。施用各菌剂均可有效促进大团聚体形成，其中单一菌剂C3的促团作用最显著，土壤平均质量直径(mean weight diameter, MWD)提升19.39%；经复合菌剂处理后的土壤肥力综合指数(integrated fertility index, IFI)达0.61，综合改良效果最佳；单一菌剂C3与复合菌剂分别使土壤EPS含量显著提高53.17%、35.79%。相关性分析结果表明，土壤EPS含量与大团聚体含量、MWD呈显著正相关，其可显著促进土壤大团聚体形成并增强其稳定性。结论 本研究筛选出的由3株耐酸产EPS微生物组成的复合菌剂可有效改良土壤结构，提升土壤综合肥力，为改良酸性土壤的生物制剂研发奠定了必要的理论基础。

Abstract:

Objective To address problems such as the poor structure and fertility degradation in strongly acidic soils, we isolated acid-tolerant exopolysaccharide (EPS)-producing microorganisms, constructed a composite microbial inoculant, and evaluated its improvement effects on the structure and comprehensive fertility of acidic soils.Methods Target strains were obtained through primary and secondary screening from strongly acidic soils (pH<4.5) in Nanchuan, Chongqing and Qujing, Yunnan. After their antagonistic activity and plant growth-promoting traits were assessed, a composite microbial inoculant was constructed. A laboratory soil culture experiment was conducted to investigate changes in nutrient contents and aggregate composition in strongly acidic soils treated with different inoculants, comprehensively evaluate the fertility-improving effects of the inoculants, and clarify the correlation between aggregate formation and EPS content.Results Three strains—Paraburkholderia fungorum C3, Burkholderia cepacia A13, and Cystobasidium minutum B14—with acid tolerance and high EPS-producing capabilities were successfully isolated and screened out. All the strains exhibited the capabilities of secreting indole-3-acetic acid (IAA), synthesizing siderophores, and solubilizing phosphorus. When these strains were applied individually or as a composite inoculant to soils, the composite inoculant showed the best effect of improving soil nutrients, increasing the content of soil organic matter, alkaline-hydrolyzable nitrogen, available phosphorus, and available potassium by 4.51%, 13.92%, 4.92%, and 3.71%, respectively. Application of all the inoculants effectively promoted the formation of soil macro-aggregates, among which the single-strain inoculant C3 had the most significant effect in promoting aggregate formation, increasing the soil mean weight diameter (MWD) by 19.39%. The integrated fertility index of the soil treated with the composite inoculant reached 0.61, indicating the optimal comprehensive improvement effect. The single-strain inoculant C3 and the composite inoculant significantly increased the soil EPS content by 53.17% and 35.79%, respectively. Correlation analysis results showed that soil EPS had significantly positive correlations with macro-aggregate content and MWD, significantly promoting the formation and enhancing the stability of soil macro-aggregates.Conclusion The composite inoculant composed of the three acid-tolerant EPS-producing strains screened in this study effectively improved the soil structure and enhanced the integrated soil fertility. These findings lay a theoretical foundation for the development of biological agents for acidic soil remediation.