【作者】 王俊峰；

【导师】 王根绪；

【作者基本信息】 兰州大学 ， 环境科学， 2008， 博士

【摘要】 青藏高原作为全球气候变化响应的敏感区和生态系统脆弱区,极易受到人类活动的干扰和全球气候变暖的影响。随着全球气候变暖和人类活动的加剧,目前青藏高原高寒生态系统,尤其是草地生态系统,正遭受着前所未有的退化、鼠害、人为破坏和近地表气温升高等一系列影响生态系统平衡等因素的干扰。作为国家自然基金重大研究计划项目“长江黄河源区高寒生态系统对全球气候变化的响应及其水文效应”研究的重要组成部分,在青藏高原风火山地区,选择具有典型性和代表性的沼泽草甸和高寒草甸两类高寒生态系统作为重点研究对象。论文重点对以下5个方面进行了详细的调查和研究:①研究区域的植被状况、不同状况下的生物量、土壤类型和气候状况等;②高寒生态系统退化对土壤理化性质和生态系统碳通量的影响;③气温升高对近地表CO₂浓度的影响及其与环境因子之间的耦合关系;④高寒生态系统净CO₂交换通量对气温升高的响应及其与环境因子之间的耦合关系;⑤气温升高对高寒生态系统碳平衡的影响。（一）、研究退化对高寒生态系统的影响,结果发现:1.不同退化程度沼泽草甸与高寒草甸下垫面土壤性质具有显著差异（方差分析,F＞7.47,P＜0.05）。未退化土壤有机质、铵氮和硝态氮氮含量均比中度退化和严重退化的大,随着退化程度的加剧,土壤养分流失严重。沼泽草甸和高寒草甸不同退化程度之间生物量也存在显著差异（方差分析,F＞4.63,P＜0.05）。在整个生长期内,其地上、地下生物量均表现为不断增加的趋势;但在同一生态系统不同退化程度之间,随着退化程度的加剧,其生物量又呈下降趋势。2.退化对高寒生态系统CO₂和CH₄通量影响显著。对于沼泽草甸,未退化CO₂排放通量分别是中度退化和严重退化的1.08—1.69倍和1.41—4.43倍;CH₄排放通量分别是中度退化和严重退化的1.09—3.5倍和2.5—11.27倍。退化越严重,CH₄和CO₂排放强度越低。对于高寒草甸,严重退化相对于未退化和中度退化表现出较高的CO₂排放和较强的甲烷吸收。CO₂排放通量分别是未退化和中度退化的1.05—78.5倍和1.04—6.28倍,对CH₄的吸收通量分别是未退化和中度退化的6.6—21倍和1.1—5.25倍。退化越严重,CO₂排放强度越大,甲烷吸收越强。3.气温、土壤含水量和土壤温度是调控沼泽草甸和高寒草甸生态系统碳通量的主要环境因子。（二）、研究气温升高对高寒生态系统近地表CO₂的影响,结果表明:对于沼泽草甸生态系统:1.近地表气温升高3—5℃和1—2℃的情况下,5cm土壤温度分别比自然状态下高出3.67℃和1.65℃;而5cm土壤水分比自然状态下分别降低2.1%和7.9%。同时,近地表气温越高,冻土的初期融化速度越快。2.整个观测期间,气温升高3—5℃和1—2℃的样点区近地表CO₂浓度平均比自然状态下分别提高29.3ppm和9.8ppm。3.空气温度、5cm土壤温度和水分含量是影响近地表CO₂浓度变化的主要环境因子。敏感性分析表明,CO₂浓度变化对5cm土壤温度和水分含量最为敏感。对于高寒草甸生态系统:1.近地表气温平均升高4.76℃和2.00℃的情况下,5cm土壤温度平均比自然状态下分别提高2.44℃和1.36℃;而5cm土壤水分平均分别下降6.97%和2.68%。2.整个观测期间,气温平均升高4.76℃和2.00℃的样点区近地表CO₂浓度平均比自然状态下分别提高34.78ppm和21.89ppm。3.空气温度、5cm土壤温度和含水量是影响高寒草甸近地表CO₂浓度的主要环境因子。敏感性分析表明,5cm土壤温度是CO₂浓度变化最敏感因子。（三）、研究气温升高对高寒生态系统NEE及其碳平衡的影响,结果表明:对于沼泽草甸生态系统:1.近地表气温升高对沼泽草甸净生态系统CO₂交换通量的影响显著。在植被生长季节,随着增温梯度的提高,生态系统净碳交换通量也逐渐增大。2.在实施增温措施的样点区,沼泽草甸生态系统每月的日平均净CO₂交换通量变化均呈单峰型曲线,碳交换通量在7月底至8月初达到最低值。6月初至8月中旬,增温梯度在3-5℃的样点区和自然状态样点区沼泽草甸均表现为CO₂吸收特征;而增温梯度在1-2℃的样点区在整个生长期均表现为CO₂排放特征。3.在不同增温梯度处理样点和自然状态样点区,沼泽草甸净CO₂交换通量均与5cm地温显著相关,相关系数均大于0.58。4.风火山地区沼泽草甸生态系统是土壤碳汇。在气温升高梯度分别为3-5℃、1-2℃和自然状态样点区,沼泽草甸的年固碳率分别达到5044.77±4.02g·m^-2·a^-1、3242.4±1.70g·m^-2·a^-1和1836.6±4.02g·m^-2·a^-1。近地表气温升高提高了生态系统的净初级生产力,对沼泽草甸生态系统碳平衡起到正反馈作用;而且近地表气温越高,碳汇效应越强。对于高寒草甸生态系统:1.近地表气温升高对高寒草甸净生态系统CO₂交换通量也产生显著影响。在植被生长季节,随着增温梯度的提高,生态系统净碳交换通量也逐渐增大。2.在实施增温措施的样点区,高寒草甸生态系统净CO₂交换通量变化曲线的斜率随着增温梯度的提高而增大,说明近地表气温越高,生态系统呼吸强度也越大,高寒草甸土壤碳库中碳流失速度加快。3.在不同增温梯度处理样点和自然状态样点区,高寒草甸净CO₂交换通量也均与5cm地温显著相关,相关系数均大于0.53。4.风火山地区高寒草甸生态系统是土壤碳弱汇。在气温升高梯度分别为3-5℃、1-2℃和自然状态样点区,其年固碳率分别达到898.67±2.38g·m^-2·a^-1、765.24±2.21g·m^-2·a^-1和543.80±1.99g·m^-2·a^-1。气温升高有助于提高生态系统的净初级生产力,使碳汇效应略有增强,对高寒草甸生态系统碳平衡起到正反馈作用。更多还原

【Abstract】 As a region with fragile ecosystems and sensitive response to the global climate change,the Qinghai-Tibetan Plateau is vulnerable to the interference from human activities and the global warming impact.With the global warming and human activity intensifying,the high-cold ecosystems,in particular the grassland ecosystems,are suffering disturbance from unprecedented degradation,rodents,and the human destruction,the near-surface warming and such as factors,impacting on the ecosystem balance,on the Qinghai-Tibetan Plateau currently.As an important composition of the major research project funded by National Natural Science foundation of China-The response and the hydrological effect of the high-cold ecosystems on the global climate change in the headwater regions of the Yangtze and the Yellow River,this study selected two typical and representative ecosystems- swamp meadow ecosystem and alpine meadow systems-to sudsy especially in the Fenghuoshan region on the Qinghai-Tibetan Plateau.This paper investigated and studied on the following several aspects in detail:（1）to research and study the vegetation conditions,biomass under different conditions,soil types and climatic conditions of the study area;（2）to study the impacts of two high-cold ecosystems’ degradation on soil physical and chemical properties and carbon fluxes from the ecosystems;（3）Under the condition of air temperature elevated,to study the influences of elevated temperature on the near-surface CO₂ concentration and the coupling relations between the CO₂ concentration and the environmental factors,at the same time,to identify the most sensitive factor to impact the change of CO₂ concentration;（4）to research the impact of elevated temperature on the net CO₂ exchange fluxes of high-cold ecosystems,and the coupling relations between the net CO₂ exchange fluxes and environmental factors;（5）to research the influences of elevated temperature on the carbon balance of two high-cold ecosystems.（Ⅰ）Research on the impact of degradation on the high-cold ecosystems,the results showed that:1.The soil properties of swamp meadow and alpine meadow with different degradation degrees showed significant differences（analysis of variance,F＞ 7.47,P＜0.05）.The contents of organic matter,ammonia nitrogen and nitrate nitrogen in soil of non-degraded meadows are higher than those of the moderately and severely degraded meadows.With the degradation becoming aggravating,the nutrients in the soil run off seriously.The biomasses among different degradation degrees of the swamp meadow and alpine meadow have significant differences（analysis of variance,F＞4.63,P＜0.05）.During the whole growing period,the biomasses of its aboveground and underground are behaving the increasing trend;however,among the different degradation degrees of the same ecosystem,gradually declining are the biomasses.2.The responses of CO₂ and CH₄ emissions from the swamp meadow are remarkable to the grassland degradation.Among them,the CO₂ emission fluxes from the non-degraded swamp meadow are 1.08-1.69 and 1.41-4.43 times higher than those from the moderately degraded and seriously degraded ones,respectively;the CH₄ emission fluxes from the non-degraded swamp meadow are 1.09-3.5 and 2.5-11.27 times higher than those from the moderately and seriously degraded one,respectively.The worse the degradation becomes,the lower are the CH₄ and CO₂ fluxes from the swamp meadow.For the alpine meadow,compared to the non-degraded and moderately degraded ones,the severely degraded meadow showed a higher CO₂ emission flux and a strong absorbing methane capacity.The CO₂ emission flux from the severely degraded ones is 1.05-78.5 and 1.04-6.28 times higher than that from the non-degraded and moderately degraded ones, respectively.The absorbing CH₄ flux of the severely degraded ones is 6.6-21 and 1.1-5.25 times higher than that of the non-degraded and moderately degraded ones,respectively.The more seriously degraded,the greater the intensity of the CO₂ emissions and methane absorption.3.Temperature,soil moisture and soil temperature are the major environmental factors to control the carbon fluxes from the swamp meadow and alpine meadow ecosystems.（Ⅱ）Research on the impact of warming on the near-surface CO₂ over the high-cold ecosystems,results showed that:For the swamp meadow ecosystem: 1.Under the conditions that the near-surface temperatures increased 3-5℃and 1-2℃respectively,the soil temperature at a depth of 5cm was higher 3.67℃and 1.65℃respectively than that at the nature condition;The soil moisture at a depth of 5cm was lower 2.1%and 7.9%respectively than that in the controlling sites;At the same time,the higher the near-surface temperature, the initial melting rate of the permafrost faster.2.During the whole observation,at the sample plots that the near-surface temperature increased 3-5℃and 1-2℃,respectively,the average CO₂ concentration was higher 29.3ppm and 9.8ppm,respectively than that over the nature sample plots.3.Air temperature,soil temperature and moisture at a depth of 5cm are the major environmental factors to impact the CO₂ concentrations.Sensitivity analysis shows that:the changes of CO₂ concentration was most sensitve to the soil temperature and moisture content at the depth of 5cm.For the alpine meadow ecosystem:1.At the conditions that the near-surface air temperatures were average 4.76℃and 2.00℃higher respectively than that at the natural state,the soil moistures at a depth of 5cm were average 6.97%and 2.68%lower than those at the natural condition,respectively.2.During the whole observation period,the near-surface CO₂ concentrations over the sample plots,which temperature was elevated 4.76℃and 2.00℃, respectively than that at the natural sample plots,were average 37.78ppm and 21.89ppm higher than those over the natral sample plots.3.Air temperature,soil temperature and moisture at a depth of 5cm are the main environmental factors to impact the near-surface CO₂ concentrations on the alpine meadows.Sensitivity analysis shows that:the changes of CO₂ concentration was most sensitve to the soil temperature at the depth of 5cm.（Ⅲ）Research on the impact of warming on the net ecosystem carbon exchange （NEE）and carbon balance of the high-cold ecosystem,results showed that:For the swamp meadow ecosystem:1.The influences of the near-surface air warming were very significant on the net ecosystem CO₂ exchange of the swamp meadows.In the growing seasons, the net ecosystem CO₂ exchanges of the swamp meadows gradually increased with the warming gradient ascending.2.At the sample plots treated with warming,the changes of the average monthly net CO₂ exchange fluxes from the swamp meadows all showed a single peak curve and the net CO₂ exchange fluxes from the swamp meadow plots all reached the most low values at the time from the end of July to the beginning of August.From early June to mid-August,the swamp meadows both at the plots with 3-5℃elevated and those at natural conditions showed a capacity of absorbed;and at the sample plots with 1-2℃elevated,the swamp meadows performed the characteristics for CO₂ emissions during the whole growing seasons.3.Regression analysis showed that:the net CO₂ exchange fluxes from the swamp meadows with three different treatments were significantly correlated with the soil temperature at a depth of 5cm and the correlation coefficients were greater than 0.58.4.The swamp meadow ecosystem in the Fenghuoshan region is a carbon sink. At the sample plots treated with 3-5℃,1-2℃elevated and natural state,the carbon sequestration rates of the swamp meadows were 5044.77±4.02g·m^-2·a^-1,3242.4±1.70g·m^-2·a^-1and 1836.6±4.02g·m^-2·a^-1, respectively.The near-surface temperature warming enhanced the respiration of the ecosystem,and took a positive feedback effect on the carbon balance. The warmer the near-surface temperature,the stronger the effect of carbon sinks.For the alpine meadow ecosystem:1.The influences of the near-surface air warming were also very significant on the net ecosystem CO₂ exchange of the alpine meadows.In the growing seasons,the net ecosystem CO₂ exchanges of the alpine meadows gradually increased with the near-surface temperatures ascending.2.At the sample plots treated with warming,the higher the near-surface air-temperature elevated,the greater the slope of the curve,which showed the changes of the net CO₂ exchange fluxes from the alpine meadow ecosystem. This denoted that the respirations of the ecosystem were greater and the loss rate of soil carbon would be accelerated.3.Regression analysis showed that:the net CO₂ exchange fluxes from the alpine meadows with three different treatments were also significantly correlated with the soil temperature at a depth of 5cm and the correlation coefficients were greater than 0.53.4.The alpine meadow ecosystem in the Fenghuoshan region is a weak carbon sink.At the sample plots treated with 3-5℃,1-2℃elevated and natural state, the carbon sequestration rates of the alpine meadows were 898.67±2.38g·m^-2·a^-1,765.24±2.21g·m^-2·a^-1and 543.80±1.99g·m^-2·a^-1, respectively.The near-surface warming on the alpine meadow ecosystem has also taken a positive feedback effect on the carbon balance,and strengthened the effect of carbon sink.更多还原