【作者】 王辉；

【导师】 彭长辉； 李红；

【作者基本信息】 西北农林科技大学 ， 生态学， 2022， 博士

【摘要】 甲烷是仅次于二氧化碳的最受关注的温室气体之一。自工业革命以来,大气中甲烷浓度已明显增加,尽管湿地、生物质燃烧和化石燃料等作为甲烷主要排放源已经被确定,但我们仍然对某些可能成为影响全球甲烷源汇变化重要因素的特定生态系统缺乏全面完整的了解。森林甲烷收支与气候变化之间的反馈是森林生态系统调节气候系统的关键环节。森林作为我国的重要碳库,在全球生态系统中具有重要的地位,而现有森林甲烷通量大多是利用箱式法进行测定,基于生态系统尺度的森林甲烷研究却鲜有报道,且不同类型森林生态系统之间甲烷通量的差异更无人报道。因此研究不同森林类型的甲烷源汇信息、时间变化特征、甲烷通量影响因素以及不同森林类型之间的差异有助于评估和预测不同森林生态系统的温室气体收支,有着重要的科学价值和实践意义。本研究以亚热带针阔混交林和暖温带落叶阔叶林为研究对象,分别于2016.1～2018.12在浙江天目山和2017.1～2020.12在河南宝天曼进行野外观测,利用先进的涡度协方差技术进行甲烷通量的持续监测。通过对甲烷通量数据的分析研究甲烷通量时间变化特征、影响因素以及甲烷的源汇信息,并对不同类型的森林生态系统进行了比较。主要结果如下:（1）亚热带针阔混交林生态系统在夏季表现为甲烷汇(吸收-0.84 g m^-2 yr^-1),而在冬季表现为甲烷排放源(排放3.815 g m^-2 yr^-1),总体表现为净源。2017-2018年甲烷的年度净收支（净源）约为1.15-4.79 g m^-2 yr^-1,这为全球气候变暖提供了正反馈。甲烷通量具有明显昼夜变化模式和季节性规律。在日尺度上,冬季有一个显著的排放峰,夏季有一个显著的吸收峰。排放高峰和吸收高峰均出现在中午。季节变化而言,所研究的森林区域在冬季表现为甲烷源,在夏季表现为汇。土壤温度和水分是影响该亚热带森林甲烷动态的主导因素。（2）暖温带落叶阔叶林生态系统在多种情景下均表现为甲烷汇,年平均甲烷吸收量分别为2017年0.256 g m^-2 yr^-1、2018年为0.324 g m^-2 yr^-1和2019年为0.516 g m^-2 yr^-1。暖温带落叶阔叶林甲烷通量在日尺度上表现出微弱的规律性变化,夏季在日出前后表现出明显的甲烷吸收峰,正午表现出明显的排放峰。冬季夜间波动不甚明显,仅在正午表现出排放峰值。在季节尺度上,该区域在冬季表现为森林甲烷的源,而在其他时间则表现为森林甲烷的汇,但是在夏季高温期会有明显的甲烷排放骤变趋势。甲烷的吸收与排放受到多种因子的影响,是土壤温度、土壤水分、辐射、相对湿度、饱和水汽压差等微气象因子共同作用的结果。其中,土壤温度和土壤水分含量是最重要的影响因子。（3）综合考虑两种生态系统的甲烷通量,不同类型森林生态系统之间具有不同的昼夜变化模式、季节变化规律以及源汇情况。亚热带针阔混交林每年都表现为净甲烷源,年平均收支为2.97±0.385 g m^-2yr^-1;而暖温带落叶阔叶林主要表现为甲烷汇,其年平均收支为-0.203±0.012 g m^-2yr^-1。亚热带针阔混交林甲烷的相对增温潜势为0.736 t CO₂ hm^-2,对增温有明显的促进作用,全国范围同类型森林的增温效应可达48838.05 t CO₂。而暖温带落叶阔叶林其甲烷相对增温潜势为-0.218 t CO₂ hm^-2,可以有效地抑制增温效应,减缓全球变暖,全国范围同类型森林的减缓效果可达110351.40t CO₂。综上所述,本研究以亚热带针阔混交林和暖温带落叶阔叶林为研究对象,系统研究了森林甲烷源汇收支信息及其变化模式。推进了生态系统尺度上山地森林甲烷通量的研究进展,为基于过程的甲烷动态模型模拟全球山地森林甲烷收支提供了独特的野外观测数据。同时,本研究探究了不同森林类型应对气候变化的规律,为我国减缓温室效应、实现绿色碳中和的目标有着重要的指导意义。更多还原

【Abstract】 Methane is one of the greenhouse gases of most concern after carbon dioxide.Atmospheric methane concentrations have increased significantly since the Industrial Revolution.Although wetlands,rice fields,biomass burning,and fossil fuels have been identified as major methane emission sources,we are still concerned about some factors that may be important factors affecting global methane source and sink changes.A comprehensive and complete understanding of specific ecosystems is lacking.The feedback between forest methane budget and climate change is a key link in forest ecosystem regulation of climate system.As an important carbon pool in my country,forests play an important role in the global ecosystem.However,there are few literature reports on forest methane,and no one has compared the differences in methane flux between different types of forest ecosystems.Therefore,studying the methane source and sink information and temporal variation characteristics of different forest types and their impact mechanisms and the differences between them will help to evaluate and predict the GHG budget in different regions,which has important scientific and practical significance.In this study,continuous flux monitoring was carried out based on eddy covariance technology in Tianmu Mountain,Zhejiang from 2016.1-2018.12 and Baotianman,Henan from 2017.1-2020.12,respectively.The open-circuit eddy correlation method is used to obtain real-time monitoring data,and the final data for analysis are obtained through data processing methods such as data preprocessing,flux calculation,data quality control and vacancy filling.Finally,the analysis of methane flux data is carried out to further study the temporal change characteristics and impact mechanism of methane flux,as well as the conversion process of methane source and sink,and compare the differences between different types of forest ecosystems,providing information for different forest types to cope with climate change.scientific basis.The main results are as follows:（1）The evergreen coniferous and broad-leaved mixed forest behaves as a methane sink in summer(absorbing-0.84 g m^-2 yr^-1),and in winter as a methane emission source(emitting 3.815 g CH₄ m^-2 yr^-1).The annual net balance（net source）of CH₄ in 2017-2018 is about 1.15-4.79 g m^-2 yr^-1,which provides a positive feedback for global warming.We also observed distinct diurnal and seasonal patterns in CH₄ flux.On the diurnal scale,there is a significant emission peak in winter and a significant absorption peak in summer.Both emission peaks and absorption peaks occurred at noon.On a seasonal scale,the studied forest area acts as a source of CH₄ in winter and a sink in summer.Soil temperature and moisture are the most important and dominant factors affecting CH₄ dynamics in subtropical forests in China.In addition,this study fills a research gap in ecosystem-scale CH₄ flux observations in upland forests,providing unique field observations for the simulation of process-based CH₄ dynamic models for global montane forest CH₄ budgets.（2）The warm temperate deciduous broad-leaved forest appears to be a methane sink under various scenarios,with the annual average methane absorption of 0.256 g CH₄ m^-2yr^-1 in 2017,0.324 g CH₄ m^-2 yr^-1 in 2018,and 0.516 g CH₄ m^-2 yr^-1 in 2019,respectively.The methane fluxes of warm temperate deciduous broad-leaved forests showed weak regular changes on the daily scale.In summer,there were obvious methane absorption peaks around sunrise,and obvious emission peaks at noon.Winter nighttime fluctuations are less pronounced,with emissions peaking only at midday.On a seasonal scale,the region behaves as a source of forest methane in winter and a sink of forest methane at other times,but there is a clear trend of abrupt changes in methane emissions during high summer temperatures.The absorption and emission of methane are affected by a variety of factors,which are the result of the combined action of micrometeorological factors such as soil temperature,soil moisture,radiation,relative humidity,and saturated water vapor pressure difference.Statistical analysis shows that soil temperature and soil moisture content are the most important influencing factors.（3）Considering the methane flux of the two ecosystems comprehensively,different forest ecosystems have different diurnal and seasonal variation patterns as well as different source and sink conditions.The average annual budget of subtropical coniferous and broadleaf mixed forest was 2.97±0.385 g m^-2 yr^-1,while that of warm temperate deciduous broad-leaved forest was-0.203±0.012 g m^-2 yr^-1.The relative greenhouse potential of methane in subtropical coniferous and broadleaf mixed forest was 0.7364 t CO₂ hm^-2,which significantly promoted global warming,and the warming effect of the same type of forest in China was 48838.05 t CO₂.However,the methane relative greenhouse potential of warm temperate deciduous broad-leaved forest is-0.218 t CO₂ hm^-2,which can effectively inhibit the warming effect and slow down global warming.The mitigation effect of the same type of forest nationwide can reach 110351.40 t CO₂.In conclusion,this study systematically studied the information of forest methane source and sink budget and its change pattern in subtropical coniferous and broadleaved mixed forest and warm temperate deciduous broad-leaved forest.In addition,this study fills a gap in the research of methane flux observation in mountain forests at the ecosystem scale,and provides unique field observation data for the simulation of global methane budget in mountain forests by process-based methane dynamic models.It also explores the law of different forest types responding to climate change,providing guidance for China to slow down the greenhouse effect and accelerate the realization of green carbon neutrality.更多还原