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| 极端干旱下内蒙古草原甲烷通量对水分响应阈值的机制研究 | |
| 其他题名 | Mechanism of methane flux response threshold to water effect in Inner Mongolia grassland under extreme drought |
| 梅美 | |
| 出版年 | 2018 |
| 学位类型 | 硕士 |
| 导师 | 郝彦宾 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 甲烷是一种重要的温室气体，虽然其在大气中的浓度低于二氧化碳，但在百年尺度上，甲烷的增温效应是二氧化碳的25倍，对全球增温贡献达25%。在全球气候变化背景下，内蒙古温带草原区干旱事件频发，干旱强度越来越大，对土壤甲烷汇功能具有重要影响。在干旱过程中，土壤对甲烷的吸收呈现先增加后减小的趋势，通量达到峰值 (吸收最大值) 所对应的土壤含水量即为土壤甲烷通量的水分响应阈值。然而，甲烷通量的水分响应阈值在不同草原生态系统并不一致，所受的调控机制也不尽相同，目前还缺乏大尺度、更深入的研究。 本研究以内蒙古温带草原土壤为研究对象，在室内对18个样点的原状土壤样品进行极端干旱处理，并通过设置不同水分和甲烷浓度梯度变化，研究极端干旱胁迫下土壤对甲烷吸收速率的变化特征，确定甲烷通量的水分响应阈值，并阐明阈值点的生物和非生物调控机制。主要研究结果如下：1. 在试验期的干旱过程中，土壤样品的甲烷通量并非都呈先增大后减小的趋势，但所有土壤样品在极端干旱条件下，仍表现为甲烷的汇。其甲烷通量峰值所对应的水分响应阈值，是某个点，或者是对应的一段水分区间。不同草原类型土壤的水分响应阈值集中于10-15%，其水分响应阈值与土壤全氮、全磷、有机碳含量均成显著的正相关关系，即随着含水量下降，土壤中养分含量越高，越容易达到水分响应阈值。2. 极端干旱胁迫下，不同草原类型的最大甲烷通量无显著性差异，但表现为典型草原>荒漠草原>草甸草原；水分响应阈值无显著性差异，但表现为草甸草原>典型草原>荒漠草原。3. 水分对甲烷吸收量的调控不是绝对性的。在甲烷浓度低于100ppmv时，水分对甲烷氧化速率起主要调控作用，而甲烷浓度高于10000ppmv，土壤水分对甲烷氧化速率无显著影响，故在高浓度甲烷环境中，会抵消水分对甲烷氧化速率的影响，且高浓度的甲烷环境更能促进甲烷氧化速率。4. 在土壤含水量持续下降过程中，土壤中甲烷氧化菌基因拷贝数变化趋势同甲烷通量相似，表现出先增大后减小的趋势。在干旱期间，甲烷氧化菌基因拷贝数在阈值点或者阈值期间达到了峰值。而在出现阈值后，甲烷氧化菌基因拷贝数迅速下降，恢复到干旱初期的水平。5. 在水分响应阈值点或阈值期甲烷氧化菌的基因拷贝数与甲烷吸收速率成显著的正相关关系，而甲烷氧化菌基因拷贝数的变化率与甲烷通量的变化率呈非线性相关。说明甲烷通量对水分的响应阈值不仅直接受到甲烷氧化菌数量和土壤甲烷浓度的调控，而且受到土壤养分含量等因素间接地影响。综上所述，甲烷通量水分响应阈值的大小与土壤碳、氮、磷含量有关。在干旱初期，随着含水量降低，土壤中甲烷浓度增加，甲烷通量逐渐增加。甲烷通量提高是因为土壤通气性的增加为甲烷氧化菌提供了更多的反应底物，促进了甲烷的吸收。在干旱后期，土壤中甲烷及氧气浓度达到大气水平，而水分成为甲烷氧化的主要限制因素。由于受水分胁迫，甲烷氧化菌在干旱后期数量显著下降，致使甲烷通量降低，出现对水分的响应阈值。因此，水分响应阈值不仅是土壤甲烷通量变化趋势的转折点，更是甲烷氧化菌群保持高活性的水分限制点。明确土壤甲烷通量的水分响应阈值所在及其调控机制，对理解未来降水变化情景下草原甲烷汇功能变化趋势，以及准确预测草原土壤甲烷吸收能力提供了理论依据。 |
| 英文摘要 | Methane is an important greenhouse gas, although its concentration is less than carbon dioxide in the atmosphere, the warming effect of methane is 25 times of carbon dioxide over a hundred year scale, and can contribute 25% to the global warming. Under the background of global climate change, intensified drought events are frequently occurred in the temperate steppe region of Inner Mongolia. During the process of drought, the soil methane flux increases first and follows the decreasing stage, thus, the soil water content corresponding to the peak flux was the water threshold of the soil methane flux. However, the water response threshold of methane flux is not consistent in different grassland ecosystems, large scale and thorough research is needed.The soil samples of the temperate grassland in Inner Mongolia were studied. These 18 soil samples were treated with extreme drought in the laboratory, with the change of soil water content and soil methane concentration during drought, the water threshold response to methane flux is determined, and its biological and abiotic regulation mechanisms are clarified. The main results are as follows:1. Not all the methane flux of soil samples were increasing or decreasing as previous research, but all the soil samples were methane sink. The water threshold is probably not a specific point but a corresponding section of soil water content, and its mainly distributed in 10-15%; the water threshold is proportional to the total nitrogen, total phosphorus and organic carbon in the soil. That is, the richer TN、TP、SOC content soil maintains, the easier to get to the water threshold.2. Under drought stress, the maximum methane flux in different grassland types has no significant difference, but the maximum methane flux in the typical steppe > desert steppe > meadow steppe. There is no significant difference in water threshold, but the water threshold of meadow steppe > typical steppe > typical steppe.3. The regulation of methane uptake by water is not absolute. When methane concentration blow magnitude of 100ppmv, soil water content play the main role in oxidation of methane. However, soil water had no significant effect on methane oxidation under 10000ppmv, high concentration methane environment can neutralize the influence of water content on methane oxidation rate, and high concentration methane environment can promote methane oxidation.4. With the soil water content declining, the gene copy number of methanotroph in the soil increased first and then decreased, while the soil methane flux presented the same tendency. During the drought, methanotroph gene copy number peaked at the water threshold. After thresholds, methanotroph gene copy number decreased rapidly, and recover to the initial stage of drought. 5. The methanotroph gene copy number is proportional to the amount of methane absorption at the water threshold, and the change rate of methanotroph gene copy number is non-linear related to the change rate of methane flux, indicating that methane flux was not only regulated by methanotroph abundance, but also other factors, but soil moisture and other factors.In conclusion, the water threshold of methane flux is related to the content of soil carbon, nitrogen and phosphorus. In the early stage of drought, soil methane concentration and methane flux increased with the water content decreasing. The increase of methane flux is due to the increase of soil aeration, which provides more substrates for methane oxidizing bacteria and accelerates the absorption of methane. In the later period of drought, soil methane and oxygen concentration reached the atmospheric level, and available water is the main limiting factor to methane oxidation. The number of methanogenic bacteria decreased significantly, resulting in the decrease of methane flux, and the water threshold presented. Therefore, the water threshold is not only the turning point of the soil methane flux, but the limit point of water to methanotrophs. To understand the water threshold of soil methane flux and its regulation mechanism, provides a basis for understanding the changing trend of methane sink function to the grassland and predicting the capacity of methane absorption in future climate scenario. |
| 中文关键词 | 极端干旱 ; 甲烷通量 ; 水分响应阈值 ; 甲烷氧化菌 ; 草原土壤 |
| 英文关键词 | extreme drought methane flux water responding threshold methanotroph grassland soil |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 生物工程 |
| 来源机构 | 中国科学院大学 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/288220 |
| 推荐引用方式 GB/T 7714 | 梅美. 极端干旱下内蒙古草原甲烷通量对水分响应阈值的机制研究[D]. 中国科学院大学,2018. |
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