王晓菲, 罗珠珠, 李玲玲, 牛伊宁, 孙鹏洲, 海龙, 李林芝. 黄土高原不同种植年限苜蓿土壤固氮微生物群落结构和丰度特征[J]. 中国生态农业学报 (中英文), 2023, 31(5): 665−676. DOI: 10.12357/cjea.20220505
引用本文: 王晓菲, 罗珠珠, 李玲玲, 牛伊宁, 孙鹏洲, 海龙, 李林芝. 黄土高原不同种植年限苜蓿土壤固氮微生物群落结构和丰度特征[J]. 中国生态农业学报 (中英文), 2023, 31(5): 665−676. DOI: 10.12357/cjea.20220505
WANG X F, LUO Z Z, LI L L, NIU Y N, SUN P Z, HAI L, LI L Z. Characteristics of structure and abundance of soil nitrogen-fixing bacterial community in alfalfa with different growing ages in the Loess Plateau[J]. Chinese Journal of Eco-Agriculture, 2023, 31(5): 665−676. DOI: 10.12357/cjea.20220505
Citation: WANG X F, LUO Z Z, LI L L, NIU Y N, SUN P Z, HAI L, LI L Z. Characteristics of structure and abundance of soil nitrogen-fixing bacterial community in alfalfa with different growing ages in the Loess Plateau[J]. Chinese Journal of Eco-Agriculture, 2023, 31(5): 665−676. DOI: 10.12357/cjea.20220505

黄土高原不同种植年限苜蓿土壤固氮微生物群落结构和丰度特征

Characteristics of structure and abundance of soil nitrogen-fixing bacterial community in alfalfa with different growing ages in the Loess Plateau

  • 摘要: 生物固氮是紫花苜蓿(Medicago sativa)土壤氮素的重要来源, 固氮微生物数量及其群落结构变化对土壤氮素供应和肥力维持起着重要作用。本研究采用Illumina MiSeq测序和荧光定量PCR技术, 探究了黄绵土区玉米农田和不同种植年限2019年(2年)、2012年(9年)、2003年(18年)紫花苜蓿地土壤nifH固氮基因丰度、nifH固氮微生物群落结构和多样性, 通过共现网络分析丰富和稀有固氮微生物的生态地位, 耦合土壤理化性质明确影响固氮微生物群落结构的主导因子。结果表明, 黄绵土固氮微生物nifH基因丰度为2.97×106~5.93×106 copies∙g−1(干土), 且表现为苜蓿地显著高于玉米农田。土壤样品经测序共获得有效序列176 367条, 主要分布在5门、8纲、11目、15科、17属。门水平上, 变形菌门和蓝藻门为主要优势类群; 属水平以斯克尔曼氏菌属和固氮弧菌属为优势属。与玉米农田相比, 多年持续种植紫花苜蓿显著提高了斯克尔曼氏菌属的相对丰度, 但其随种植年限延长呈降低趋势。长期种植紫花苜蓿促生了固氮菌属、伯克氏菌属、弗兰克氏菌属、中慢生根瘤菌属、地杆菌属和慢生根瘤菌属等生理类群, 同时也使得梭状杆菌属、红假单胞菌属和三离藻属消亡。RDA分析发现, 固氮微生物不同种群对环境因子的响应并不一致, 具有各自的生态位, 但土壤全磷是影响土壤固氮微生物群落结构的主导环境因子, 其次是有机碳和硝态氮。分子生态网络分析表明固氮菌生态网络中丰富类群占据生态系统核心地位, 且物种间均为协同合作关系, 群落结构相对稳定, 对环境变化具有较强的适应能力。综上, 黄土高原半干旱区种植紫花苜蓿显著提高了土壤nifH基因丰度, 改变了固氮微生物nifH群落结构, 该结果可为黄绵土固氮微生物多样性研究和紫花苜蓿适宜种植年限的确定提供基础数据和理论依据。

     

    Abstract: Biological nitrogen fixation is a major nitrogen source in alfalfa fields, and the nitrogen supply and soil fertility can be largely affected by the composition and quantity of the nitrogen-fixing bacterial community. In this study, a field experiment was conducted to explore the soil nitrogen-fixing bacterial community structure and abundance characteristics in loessal soil with different alfalfa growing ages (2, 9 and 18 years planted in 2019, 2012, and 2003, respectively), using farmland (maize field) as the control. The fluorogenic quantitative real-time PCR technique was adopted in the experiment, using the high-throughput sequencing platform Illumina MiSeq to target the nifH gene. We analyzed the ecological status of abundant and rare nitrogen-fixing microorganisms through co-occurrence networks and identified the dominant factors affecting the community structure of nitrogen-fixing microorganisms by soil coupling the physical and chemical properties. The results showed that long-term planting of alfalfa increased the organic carbon, total nitrogen, and soluble carbon contents of the soil. The nifH gene abundance ranged from 2.97×106 copies∙g−1 to 5.93×106 copies∙g−1 in dry soil and was significantly higher in alfalfa fields than in farmland. The correlation analysis between the abundance of nifH gene of nitrogen-fixing microorganisms and soil physicochemical factors showed that nifH gene abundance in the soil was positively correlated with bulk density (P=0.009) and soluble carbon content (P=0.005), positively correlated with total nitrogen (P=0.044) and available potassium (P=0.013) contents, and negatively correlated with total phosphorus content (P=0.000) and nitrate content (P=0.023). A total of 176 367 valid sequences were obtained, belonging to five phyla, eight classes, 11 orders, 15 families, and 17 genera. Proteobacteria and Cyanobacteria were the dominant phyla, accounting for 95.9%−98.9% and 0.2%−1.8% of the total sequences of the samples, whereas Skermanella and Azohydromonas were the dominant genera, accounting for 82.2%–87.6% and 1.6%–4.6%, respectively. Compared with farmland, continuous alfalfa planting significantly increased the relative abundance of Skermanella, but its’ relative abundance decreased with increasing alfalfa planting years. Long-term cultivation of alfalfa propagated microbial taxa, including Azotobacter, Burkholderia, Frankia, Mesorhizobium, Geobacter, and Bradyrhizobium; whereas Clostridium, Rhodopseudomonas, and Trichormus were sterilized. Redundancy analysis (RDA) showed niche differentiation for the nitrogen-fixing bacterial community in response to environmental factors, but total phosphorus, organic carbon, and nitrate-nitrogen in the soil were the dominant environmental factors for the nitrogen-fixing bacterial community structure. Analysis of the molecular ecological network showed that there were 520 nodes and 4170 edges in the network of nitrogen-fixing microorganisms in maize fields and alfalfa soil, among which 24 nodes belonged to the abundant group, 93 nodes belonged to the rare group, and 403 nodes belonged to the transitional group. There was one internal connection of abundant taxa, 2187 internal connections of transitional taxa, and 358 internal connections of rare taxa. Nitrogen-fixing bacteria have a cooperative relationship in their ecological network, with a relatively stable community structure and strong adaptability to environmental changes. This study provides basic data and a theoretical basis for the diversity of nitrogen-fixing microorganisms in loess soil and the determination of a suitable planting period for alfalfa.

     

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