| 摘要: |
| 溶解有机质（DOM）是水生生态系统的重要能量和营养源，其N/C等元素化学计量学能够反映湖泊沉积物营养物质来源，相关研究有助于揭示全球变暖和水体富营养化的影响机制。本研究聚焦高分辨率质谱技术所获DOM的N/C比值，通过meta分析从宏观角度考察全球湖泊、河流、海洋和泥炭地等多生境的N/C比值的全球分布情况，结果表明，河流水体、沉积物和污水等生境的N/C均值均显著高于泥炭地，分别为0.050±0.062、0.050±0.014、0.083±0.084和0.026±0.037；水体N/C比值主要受海拔（即温度）、pH、氨氮和溶解有机碳等显著影响，而泥炭地等陆地N/C比值主要受pH、总溶解有机氮和溶解有机碳的影响。进一步，依托云南老君山海拔梯度开展模拟温度变化和营养富集的微宇宙实验定量解析其影响机制，并根据沉积物DOM分子转换数将总分子划分为高活性和低活性两类，探究总分子及其两类组分的N/C比值对温度和营养富集的响应规律。溶解有机质 N/C 均值为0.112±0.020，其中高活性分子（0.119±0.017）显著高于低活性分子（0.109±0.034）。总分子N/C 比值主要受亚硝酸盐和硝酸盐等营养盐的影响，解释量为63.43%；高活性分子 N/C 比值主要受营养盐和能量供应（比如溶解有机碳、总有机碳和叶绿素a等）的影响，而低活性分子N/C比值主要受营养盐的影响。结构方程模型分析表明，营养富集对总分子N/C 比值的影响高于温度，主要通过能量供应和营养盐的间接作用而发挥影响；对于高活性分子，营养盐主要通过能量供应的间接作用影响N/C 比值；而对于低活性分子，主要通过营养盐发挥直接作用。本研究结果首次探讨了全球不同生境N/C比值的分布格局，揭示了沉积物溶解有机质N/C比值对全球变暖和营养富集的响应规律和机制，为更好理解和预测未来全球变化背景下溶解有机碳稳定性提供科学参考。 |
| 关键词: 湖泊 沉积物 溶解有机质 氮碳比 全球变暖 富营养化 |
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| 基金项目:国家自然科学基金项目（面上项目，重点项目，重大项目） |
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| The N/C ratios of dissolved organic matter and their response to lake warming and nutrient enrichment* |
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Chen Ming,Hu Ang,Han Lei,Wang Jianjun
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Key Laboratory of Lake and Watershed Science for Water Security, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences
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| Abstract: |
| Dissolved organic matter (DOM) is an important source of energy and nutrients for aquatic ecosystems, and its elemental stoichiometry, such as N/C ratios, can reflect the nutrient sources of lake sediments, and its study can help reveal the mechanisms of the impacts of global warming and eutrophication on the water bodies. In this study, we focused on the N/C ratios of DOM obtained by high resolution mass spectrometry, and examined the global distribution of N/C ratios of several habitats such as lakes, rivers, oceans and peatlands by meta-analysis. The results showed that the mean values of N/C of habitats such as river waters (0.050±0.062), sediments (0.050±0.014) and wastewaters (0.083±0.084) showed significantly higher mean values than those of peatlands (0.026±0.037). The N/C ratios of waters were significantly affected by temperature, pH, ammonia nitrogen (NH4+-N) and dissolved organic carbon, whereas N/C ratios of terrestrial ecosystems such as peatlands were mainly affected by pH, total dissolved organic nitrogen and dissolved organic carbon. Furthermore, to explore the patterns of all molecules and their two fractions in response to temperature and nutrient enrichment, a microcosm experiment with simulated temperature changes and nutrient enrichment was conducted to quantitatively analyses the influence mechanism based on the elevational gradient of Laojun Mountain in Yunnan Province, and classified all molecules into two categories of active and inactive molecules according to the sediment DOM molecular transformation number. The N/C ratio of DOM was averagely 0.112±0.020 for all molecules, and the active molecules (0.119±0.017) were significantly higher than inactive molecules (0.109±0.034). The N/C ratios of all molecules were mainly influenced by nutrients (e.g., nitrite and nitrate) with an explanation of 63.43%; the N/C ratios of active molecules were mainly influenced by nutrients and energy supply (e.g., dissolved organic carbon, total organic carbon and chlorophyll a), whereas the N/C ratios of inactive molecules were mainly influenced by nutrients. Structural equation modelling (SEM) analyses further showed that nutrient enrichment had a greater effect on the N/C ratios of total molecules than temperature changes, mainly through the indirect effects of energy supply and nutrients; for active molecules, nutrients affected the N/C ratios through the indirect effect of energy supply; and for inactive molecules, nutrients showed mostly direct effect. Overall, our study explored for the first time the distribution pattern of N/C ratios in various habitats around the globe, revealed the response patterns and mechanisms of sediment dissolved organic matter N/C ratios to global warming and nutrient enrichment, and provided scientific evidence for a better understanding and prediction of the stability of dissolved organic carbon under a changing world. |
| Key words: lake sediments dissolved organic matter N:C ratio global warming eutrophication |
