青海湖岸带土壤与沉积物的地化特征与细菌群落对水位上升的响应

Response of geochemistry and bacterial communities to water-level rise in the soil and sediment of the coastal zone in Qinghai Lake

摘要:

【目的】探究青海湖岸带土壤与沉积物的地化特征与细菌群落对水位扩张的响应。【方法】从岸上至岸下沿垂直青海湖岸带方向，采集距离湖面不同高度土壤(土壤：S1、S2)、岸边不同水深表层沉积物(过渡区：E0、E6、E17)及湖心表层沉积物(沉积物：D1、D2)样品，土壤与沉积物水深(土壤水深表示为负数)从小到大的变化表征岸边土壤被淹水转变为沉积物的过程。采用地球化学分析和16S rRNA基因高通量测序技术，探究岸带土壤与沉积物样品中的地化特征与微生物群落构成。【结果】青海湖水位上升导致的生境转变对岸带土壤与沉积物的理化性质、营养水平、有机碳类型等地化特征产生显著影响。具体表现为，随着水位升高，岸带土壤与沉积物的pH、矿物结合态有机碳含量显著升高，而碳氮比值、可溶性有机碳(dissolved organic carbon, DOC)、颗粒态有机碳含量显著下降。随着水位上升，青海湖岸带被淹没土壤的细菌群落多样性下降，且群落结构发生明显变化。这种变化与环境因子变化密切相关，具体表现为，细菌群落物种丰富度指数和香农多样性指数随着水位上升呈下降趋势；活性金属结合态有机碳含量与细菌群落多样性的变化密切相关；理化性质(pH)、营养水平[总有机碳(total organic carbon, TOC)含量]、有机碳质量(碳氮比值及活跃碳库II、矿物结合态有机碳含量)是影响细菌群落结构的重要环境因子，且理化性质、营养水平、有机碳质量三者对细菌群落结构差异的影响贡献相当。【结论】青海湖水位上升显著影响了岸带土壤与沉积物的理化性质、营养水平及有机碳质量等地化特征，并重塑了细菌群落结构。这意味着在青藏高原湖泊广泛扩张的背景下，青藏高原湖泊的区域碳循环稳态将随之发生改变。本研究对湖泊扩张过程中土壤与沉积物的微生物群落演变规律及生态系统碳稳定性评价提供了一定的数据基础和理论支撑。

Abstract:

[Objective] To investigate the response of geochemistry and bacterial communities to water-level rise in the soil and sediment of the coastal zone of Qinghai Lake. [Methods] Surface samples were collected from the onshore soil (soil: S1, S2), littoral zone (transition: E0, E6, E17) and deep sediment (sediment: D1, D2) along the direction perpendicular to the shoreline near the Bird Island of Qinghai Lake. The water depth of the soil and sediment samples (soil water depths were expressed as negative numbers) was employed to characterize the transformation of shoreline soil into sediment caused by inundation. Geochemical analysis and 16S rRNA gene high-throughput sequencing were employed to explore the geochemical characteristics and microbial community composition in the collected soil and sediment samples. [Results] (1) The water level rise of Qinghai Lake significantly affects the geochemical characteristics, nutrient levels, and organic carbon types in the soils and sediments of the coastal zone. Specifically, the pH and mineral associated organic carbon contents of the soil and sediment in the shore zone increased significantly while the C/N value and the contents of dissolved organic carbon (DOC) and particulate organic carbon decreased significantly with the increase of water level; (2) The water level rise of Qinghai Lake will reduce the diversity of bacterial communities and change their community structure in the coastal soils and sediments. These changes in bacterial communities are closely related to changes in environmental factors caused by water level rise. Specifically, after the onshore soil was inundated by water level rise, the bacterial communities inhabiting it exhibited a decrease in the number of operational taxonomic unit (OTU) and Shannon diversity index; the changes of bacterial community diversity was closely related to the content of organic carbon bound with active metal; the important environmental factors that affect bacterial community structure included physicochemical properties (pH), nutrient level (total organic carbon content), and organic carbon quality (C/N value, organic carbon pool II, and mineral associated organic carbon content). Physicochemical properties, nutrient level, and organic carbon quality contributed equally to the differences in bacterial community structure. [Conclusion] The water level rise of Qinghai Lake has significantly affected the physiochemical characteristics, nutrient levels, and organic carbon quality of coastal soil and sediment, and reshaped the bacterial community structure. This implies that the regional carbon cycle homeostasis of the Qinghai-Tibetan lakes will change in the context of the extensive expansion of lakes on the Qinghai-Tibet Plateau. This study provides a data base and theoretical support for the evolution of soil and sediment microbial communities and the evaluation of ecosystem carbon stability in response to lake expansion.