黄土高原紫花苜蓿地土壤AMF群落结构及其组装机制

Soil AMF community structure and assembly mechanism of Medicago sativa field in Loess Plateau

  • 摘要: 为揭示多年种植紫花苜蓿对土壤丛枝菌根真菌(AMF)群落结构和多样性的影响, 本研究通过布设在黄土高原半干旱区的田间试验, 基于2019年(L2019)、2012年(L2012)和2003年(L2003)建植的紫花苜蓿田, 以农田玉米为对照, 采用高通量测序和PCR技术, 结合分子生态网络研究不同种植年限紫花苜蓿地土壤AMF群落组成和丰度, 并基于零模型揭示了土壤AMF群落的组装过程。结果表明: 黄绵土区AMF属于球囊菌门的1纲4目7科7属, 球囊霉属、类球囊霉属和多孢囊霉属为紫花苜蓿地和农田土壤共有类群, 且均以球囊霉属(65.15%~99.12%)为优势属, 其主要贡献了不同处理分组中土壤AMF群落结构的改变。长期种植紫花苜蓿使和平囊霉属和无梗囊霉属消亡, 但促生了双型囊霉属和盾巨孢囊霉属, 其中双型囊霉属相对丰度表现为L2019处理显著高于其他处理(P<0.05)。网络关联分析发现, 高丰度的球囊霉属和类球囊霉属之间呈现负相关, 而低丰度的和平囊霉属和无梗囊霉属之间呈现正相关。基于零模型的AMF群落组装结果表明, 农田与L2019处理由确定性过程主导(66.67%), L2012和L2003处理由随机性过程主导(100%), 这表明长期种植紫花苜蓿形成稳定的土壤环境使其随机性过程增加, 利于维持人工草地生态系统功能的可持续性和稳定性。

     

    Abstract: Arbuscular mycorrhizal fungi (AMF) mediate the interactions between plants and soils, play crucial roles in terrestrial symbiosis, and are important components of soil microbial communities. However, information on the variations of soil AMF communities with respect to the loess soil properties is limited. Therefore, the present study investigated soil AMF diversity, community structure, and physicochemical properties in Medicago sativa fields and farmland in the Loess Plateau semi-arid area. Soil samples (0–20 cm) were collected in June 2021 from four treatments: maize (Zea mays) field (Farmland) and M. sativa fields established in 2019 (L2019), 2012 (L2012), and 2003 (L2003). Illumina MiSeq high-throughput sequencing and real-time fluorescent quantitative PCR were used to explore the structure and diversity of the AMF communities under the four treatments (Farmland, L2003, L2012, and L2019). Statistical methods (redundancy analysis and molecular ecological network analysis) were used to explore the relationship between soil physicochemical properties and the AMF community. Zero-model analysis was used to reveal the assembly process of the soil AMF community. The results showed that long-term alfalfa planting decreased soil total phosphorus and available phosphorus contents. The AMF gene abundance ranged from 1.02×104 to 1.50×104 copies∙g−1 in dry soil, which was significantly higher in M. sativa field planted in 2003 than in other treatments (P<0.05). Correlation analysis between the abundance of AMF genes and physicochemical factors showed that soil AMF gene abundance was positively correlated with total nitrogen content and negatively correlated with total phosphorus and available phosphorus contents. One class, four orders, seven families, and seven genera of AMF were identified. Glomus, Diversispora, and Paraglomus were the common genera of M. sativa fields and Farmland, and the dominant genera of M. sativa fields and Farmland were Glomus (65.15%−99.12%), mainly contributing to the changes of soil AMF community structure in different treatment groups. Long-term cultivation of M. sativa propagated rare microbial taxa, including Ambispora and Scutellospora, whereas Pacispora and Acaulospora were sterilized. Ambispora was significantly higher in M. sativa field planted in 2019 than in the other treatments (P<0.05). The analysis of the molecular ecological network showed that there were highly abundant genera (Glomus and Paraglomus) that had cooperative relationships in the ecological network, whereas the low-abundance genera (Pacispora and Acaulospora) had competitive relationships in the ecological network. RDA showed no main environmental factors affecting the AMF community structure. The null model was used to infer AMF community assembly processes. In Farmland and M. sativa field established in 2019, community mechanisms were dominantly assembled with deterministic processes (66.67%), with heterogeneous selection contributing the most. For the M. sativa field established in 2012 and 2003, the community mechanisms were dominantly assembled with random processes (100.00%); the undominated processes contributed the most to M. sativa field planted in 2012, and dispersal limitation contributed the most to M. sativa field planted in 2003. The Mantel test showed no main environmental factors driving AMF community assembly. Long-term cultivation of M. sativa increases the number of random processes. This is beneficial for maintaining the sustainability and stability of the artificial grassland ecosystem functions. In summary, long-term M. sativa planting significantly affected the composition of soil AMF communities. This study provides basic data and a theoretical basis for further studies on the microbial mechanisms of AMF on the Loess Plateau after years of M. sativa planting.

     

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