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.
-
Key words:
- Medicago sativa /
- Arbuscular mycorrhizal fungi /
- Community structure /
- Community assembly /
- Loessal soil
-
图 1 不同处理土壤丛枝菌根真菌(AMF)群落多样性指数
Farmland、L2019、L2012、L2003分别表示农田、2019年建植紫花苜蓿、2012 年建植紫花苜蓿和2003年建植紫花苜蓿。Farmland, L2019, L2012, and L2003 denote farmland and Medicago sativa fields planted in 2019, 2012, and 2003, respectively.
Figure 1. Diversity indexes of arbuscular mycorrhizal fungi (AMF) community under different treatments
图 2 不同处理土壤丛枝菌根真菌(AMF)群落主坐标分析
Farmland、L2019、L2012、L2003分别表示农田、2019年建植紫花苜蓿、2012 年建植紫花苜蓿和2003年建植紫花苜蓿。Farmland, L2019, L2012, and L2003 denote farmland and Medicago sativa fields planted in 2019, 2012, and 2003, respectively.
Figure 2. Principal co-ordinates analysis (PcoA) of abundance of soil arbuscular mycorrhizal fungi (AMF) communities under different treatments
图 3 不同处理土壤丛枝菌根真菌(AMF)属水平群落结构(A)和双型囊霉属相对丰度(B)
Farmland、L2019、L2012、L2003分别表示农田、2019年建植紫花苜蓿、2012 年建植紫花苜蓿和2003年建植紫花苜蓿。*表示处理间差异显著(P<0.05)。Farmland, L2019, L2012, and L2003 denote farmland and Medicago sativa fields planted in 2019, 2012, and 2003, respectively. * indicates significant differences among treatments at P<0.05.
Figure 3. Relative abundance of soil arbuscular mycorrhizal fungi (AMF) community at the genus level (A) and relative abundance of Ambispora (B) under different treatments
图 5 不同处理方式下土壤丛枝菌根真菌(AMF)群落与土壤理化因子冗余分析
Farmland、L2019、L2012、L2003分别表示农田、2019年建植紫花苜蓿、2012 年建植紫花苜蓿和2003年建植紫花苜蓿。SW、BD、OC、TN、TP、AP、AK分别表示土壤水分、容重、有机碳、全氮、全磷、速效磷、速效钾, Glomus、Paraglomus、Diversispora、Scutellospora、Ambispora、 Acaulospora 和pacispora分别表示球囊霉属、类球囊霉属、多孢囊霉属、盾巨孢囊霉属、双型囊霉属、无梗囊霉属及和平囊霉属。Farmland, L2019, L2012, and L2003 denote farmland and Medicago sativa fields planted in 2019, 2012, and 2003, respectively. SW, BD, OC, TN, TP, AP, AK are soil water, bulk density, organic carbon, total nitrogen, total phosphorus, available phosphorus, available potassium, respectively.
Figure 5. Redundancy analysis (RDA) of abundance of soil arbuscular mycorrhizal fungi (AMF) communities and soil physicochemical properties under different treatments
图 6 不同处理土壤丛枝菌根真菌(AMF)群落组装生态过程
Farmland、L2019、L2012、L2003分别表示农田、2019年建植紫花苜蓿、2012 年建植紫花苜蓿和2003年建植紫花苜蓿。Stochasticity: 随机性过程;Und: 非主导过程; Dil: 扩散限制; Determinism: 确定性过程; Hod: 同质性扩散; Hos: 同质性选择; Hes: 异质性选择。Farmland, L2019, L2012, and L2003 denote farmland and Medicago sativa fields planted in 2019, 2012, and 2003, respectively. Und: undominated processes; Dil: dispersal limitation; Hod: homogenizing dispersal; Hos: homogeneous selection; Hes: heterogeneous selection.
Figure 6. Ecological processes governing abundance of soil arbuscular mycorrhizal fungi (AMF) community assembly under different treatments
表 1 不同处理土壤基本理化性状及丛枝菌根真菌(AMF)基因丰度
Table 1. Soil physicochemical properties and abundance of arbuscular mycorrhizal fungi (AMF) gene under different treatments
指标 Index Farmland L2019 L2012 L2003 土壤水分 Soil water (%) 15.65±0.76a 8.76±0.46b 8.72±0.34b 9.62±0.13b 容重 Bulk density (g∙cm−3) 1.18±0.01a 1.21±0.01a 1.23±0.02a 1.24±0.03a 有机碳 Organic carbon (g∙kg−1) 10.50±0.20b 9.83±0.21b 9.89±0.05b 11.49±0.32a 全氮 Total nitrogen (g∙kg−1) 0.92±0.03b 0.77±0.02c 0.85±0.05bc 1.11±0.05a 硝态氮 Nitrate nitrogen (mg∙kg−1) 23.14±0.33a 13.93±0.07c 12.35±0.07d 14.85±0.08b 全磷 Total phosphorus (g∙kg−1) 0.99±0.01a 0.93±0.01b 0.86±0.03c 0.82±0.01c 速效磷 Available phosphorus (mg∙kg−1) 6.21±0.05a 5.02±0.15b 3.92±0.13c 3.54±0.09d 速效钾 Available potassium (mg∙kg−1) 223.00±11.14a 222.00±2.89a 228.67±7.06a 229.33±0.88a pH 8.38±0.03a 8.49±0.01a 8.47±0.04a 8.45±0.03a AMF基因丰度
Abundance of AMF gene [×104 copy∙g−1(dry soil)]1.15±0.01bc 1.02±0.00c 1.26±0.04b 1.50±0.08a 数据为平均值±标准误(n=3), 同行不同小写字母表示不同处理间差异显著(P<0.05), Farmland、L2019、L2012和L2003分别表示农田、2019年建植紫花苜蓿、2012年建植紫花苜蓿和2003年建植紫花苜蓿。Data in table are mean ± standard error (n=3). Different lowercase letters in the same line indicate significant differences among different treatments (P<0.05). Farmland, L2019, L2012, and L2003 denote farmland and Medicago sativa fields planted in 2019, 2012, and 2003, respectively. 表 2 丛枝菌根真菌(AMF)基因丰度与土壤理化因子相关分析
Table 2. Correlation analysis of arbuscular mycorrhizal fungi (AMF) gene abundance and environmental factors
AMF SW BD OC TN NO3−-N TP AP AK pH AMF 1.000 SW 0.105 1.000 BD 0.298 −0.495 1.000 OC 0.522 0.522 0.165 1.000 TN 0.789** 0.474 0.023 0.786** 1.000 NO3−-N 0.007 0.888** −0.488 0.648* 0.523 1.000 TP −0.711** 0.438 −0.627* −0.202 −0.304 0.529 1.000 AP −0.774** 0.326 −0.560 −0.263 −0.397 0.396 0.961** 1.000 AK 0.462 −0.042 0.229 0.109 0.305 −0.112 −0.385 −0.392 1.000 pH −0.102 −0.615* 0.456 −0.252 −0.515 −0.566 −0.327 −0.322 0.162 1.000 **: P<0.01; *: P<0.05。AMF、SW、BD、OC、TN、TP、AP、AK分别表示AMF基因丰度、土壤水分、容重、有机碳、全氮、全磷、速效磷、速效钾。In the table, AMF, SW, BD, OC, TN, TP, AP, AK are abundance of AMF gene, soil water, bulk density, organic carbon, total nitrogen, total phosphorus, available phosphorus, available potassium. 表 3 不同处理方式间丛枝菌根真菌(AMF)群落组成差异的优势属贡献率
Table 3. Contribution rates of dominant genus to abundance of arbuscular mycorrhizal fungi (AMF) community compositions under different treatments
% 分组
Group球囊霉属
Glomus类球囊霉属
Paraglomus多孢囊霉属
Diversispora盾巨孢囊霉属
Scutellospora双型囊霉属
Ambispora无梗囊霉属
Acaulospora和平囊霉属
PacisporaFarmland vs L2019 48.08 5.27 1.23 0.00 0.93 0.18 0.18 Farmland vs L2012 49.00 1.91 0.56 1.39 0.35 0.27 0.27 Farmland vs L2003