咸海湖泊退缩对岸边土壤真菌和植物内生真菌的影响研究

Influence of lake desiccation on the entophytic and soil fungal communities on the Aral Sea shore

摘要:

[目的] 研究咸海岸边不同暴露时期土壤带的土壤真菌和植物内生真菌群落构成及其对湖泊干涸的响应。[方法] 从咸海湖岸远端（土壤带的暴露时间最长）到湖岸近端（土壤带的暴露时间最短）的不同土壤带采集土壤样品，对其进行地球化学和矿物学分析。同时也采集各土壤带的土壤样品和优势植物，通过ITS基因高通量测序方法分析土壤真菌和植物内生真菌群落构成，进而探讨其如何响应湖泊干涸（如盐度升高、矿物组分变化、植物种类丰富度变化等）过程。[结果] 持续暴露的咸海湖床从湖泊远岸到湖泊近岸形成了一个连续的盐度梯度：E48（暴露于1970年之前，总可溶解盐0.5±0.5 g/L）；E38（暴露于1980年之前，总可溶解盐0.4±0.2 g/L）；E28（暴露于1990年之前，总可溶解盐23.3±2.1 g/L）；E18（暴露于2000年之前，总可溶解盐23.7±7.5 g/L）；E9（暴露于2009年之前，总可溶解盐71.3±6.1 g/L）；E1（暴露于2017年之前，总可溶解盐62.9±10.7 g/L）和E0（2018年湖岸线附近沉积物样品，总可溶解盐69.9±8.3 g/L）。咸海岸边不同土壤带分布着不同的植物：梭梭（Haloxylon ammodendron）在E48和E38区域中占优势地位；滨藜（Chenopodium album）在E28、E18和E9区域占优势；而在E1和E0区域无可见植物物种分布。另外，咸海岸边不同土壤带的主要矿物成分也存在差异：粘土矿物和蒸发岩的含量从咸海湖岸远端到湖岸近端逐渐增加，而碳酸盐矿物含量逐渐减少。咸海岸边不同土壤带土壤样品优势真菌类群（>5%）为散囊菌纲（Eurotiomycetes）、粪壳菌纲（Sordariomycetes）、锤舌菌纲（Leotiomycetes）、座囊菌纲（Dothideomycetes）、黑粉菌亚门（Ustilaginomycotina）和伞菌纲（Agaricomycetes），且按植物种类丰富度进行聚类。而植物样品优势真菌类群为未知真菌门类（>97.8%），且按植物种类进行聚类。线性回归结果显示，咸海岸边不同土壤带土壤样品真菌群落差异性与暴露时间距离具有显著相关（R²=0.32，P<0.05），而与总可溶解盐差异则无明显相关性。而植物内生真菌群落差异性与暴露时间距离/总可溶解盐差异之间均无显著相关。Mantel检验结果显示，咸海岸边不同土壤带土壤真菌群落与植物种类丰富度和矿物成分组成（如白云石、方解石、微斜长石和石膏）呈显著相关（P<0.05），其中植物种类丰富度和方解石含量的相关性系数最大；植物内生真菌群落与方解石含量之间呈显著相关（P<0.05）。[结论] 咸海岸边不同暴露时期土壤带的土壤真菌和植物内生真菌种群结构具有时空差异，与植物种类丰富度和特定矿物组成相关，而与总可溶解盐无显著相关。

Abstract:

[Objective] To explore the diversity and community compositions of onshore soil and plant endophytic fungi in the soil zones at different exposure periods and their response to continuous lake desiccation in the Aral Sea. [Methods] Soil samples were collected from farshore (exposed before 1970) towards the present shoreline in the Aral Sea, followed by geochemistry and mineralogy analysis. At the same time, soil samples and dominant aboveground plants from different onshore soil zones were collected, and their fungal diversity were analyzed by ITS gene high-throughput sequencing. The fungal response to lake desiccation (such as salinity, mineralogy and plant species) were explored. [Results] The results showed that the continuously exposed lake bed formed an increasing gradient of total soluble salts:E48 (exposed before 1970, total soluble salts (in abbr. TSS):0.5±0.5 g/L);E38 (exposed before 1980, TSS:0.4±0.2 g/L);E28 (exposed before 1990, TSS:23.3±2.1 g/L);E18 (exposed before 2000, TSS:23.7±7.5 g/L);E9 (exposed before 2009, TSS:71.3±6.1 g/L);E1 (exposed in 2017, TSS:62.9±10.7 g/L); E0 (the present shoreline in 2018, TSS:69.9±8.3 g/L). These soil zones were inhabited by different plants:Haloxylon ammodendron were dominated in the E38 and E28 zones; Chenopodium album were dominated in the E28, E19 and E9 zones; and no visible plants were found in the E1 and E0 zones. In addition, the mineralogical composition varied among different soil zones:the contents of clay mineral and evaporites generally increased from farshore towards the present shoreline of the Aral Sea, while the content of carbonates gradually decreased. The dominant fungal communities (>5%) in the studied soil samples were Eurotiomycetes, Sordariomycetes, Leotiomycetes, Dothideomycetes, Ustilaginomycotina and Agaricomycetes, and were clustered by plant species richness. While a large number of unknown fugal species (>97.8%) were dominated in the endophytic fungal communities, and were clustered by plant species. Linear regression showed that the fungal community differences in the soil sample from different onshore soil zones had a significant (R²=0.32, P<0.05) correlation with the exposure time difference, whereas there was no significant correlation with the difference in total soluble salts. In addition, there was no significant difference between the plant endophytic fungal community difference and exposure time distance and total soluble salts difference. Mantel test showed that fungal communities in different soil zones had significant (P<0.05) correlations with plant species richness and dolomite, calcite, microcline and gypsum. Among them, plant species richness and calcite were the most important factors influencing on soil fungal communities. There was a significant (P<0.05) correlation between the plant endophytic fungal community and calcite. [Conclusion] The community compositions of soil fungi and plant endophytic fungi in different Aral Sea soil zones show temporal and spatial variations, which could be ascribed to plant species (richness) and specific mineral compositions, but not significantly correlated with total soluble salts.