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气候变化对高寒草甸生态系统温室气体通量特征的影响
Alternative TitleImpact of Climate Change on GHG flux Characteristics of Alpine Meadow Ecosystems
陈晓鹏
Subtype博士
Thesis Advisor王根绪
2017
Degree Grantor中国科学院大学
Place of Conferral北京
Degree Discipline自然地理
Keyword气候变暖 氮沉降 温室气体 高寒草甸 高寒湿地
Abstract高寒草甸是青藏高原多年冻土区典型生态系统,其不仅具有重要的生态系统服务功能,更是当地牧民重要的生产资料。然而,在过去的50年间,青藏高原平均气温和年均降水量以每10年0.3 °C 和9.1 mm的速度不断增加,氮沉降水平虽然 < 2 Kg hm-2 a-1,小于中国其他地区,但也呈增加趋势。这些气候因素变化必然影响高寒草甸生态系统碳、氮循环。温室气体通量变化作为生物圈与大气进行碳、氮交换的重要途径,探究气候变化对温室气体通量变化的影响,是人类深入了解气候变化对高寒草甸生态系统碳、氮循环影响的重要环节。虽然有关增温和氮沉降增加对高寒生态系统温室气体通量的研究已经大量开展,但对于两者交互作用的原位观测研究报告还很少见。尤其在多年冻土区,温室气体通量变化很可能与活动层融化深度及活动层土壤温度、水分有着密切关联,而呈现出与非冻土区不同的季节变化特征。因此,以多年冻土区土壤温度变化而划分的生长季的不同阶段温室气体通量变化是又一重要的研究课题。本研究以长江源区高寒草甸和高寒沼泽草甸为研究对象,依托风火山模拟增温和氮沉降试验场,对两种类型高寒草甸在生长季前期、中期和后期的主要温室气体通量(生态系统呼吸、CH4和N2O通量)变化进行原位观测,并且通过对比在干、湿年份结果的差异,意图揭示未来气候变化(气候变暖、氮沉降增加和降水量变化)对高寒草甸生态系统温室气体通量变化的影响。基于本研究得到的主要结果如下:1. 模拟增温(4.5 °C)促进了高寒草甸的生长季生态系统呼吸、CH4吸收和N2O排放,增幅分别为73.5%、65.9%和431.6%。氮沉降增加对高寒草甸三种温室气体通量均无显著影响。氮沉降增加显著促进了增温情境下高寒草甸10.3%的CH4吸收和27.2%的N2O排放(相比于单独的增温),但对高寒草地生态系统呼吸无显著影响。氮添加倾向于削弱增温对高寒草甸生态系统呼吸的作用,促进其CH4吸收和N2O排放,表明高寒草甸温室气体通量变化对未来气候变暖和氮沉降增加同时具有正的和负的反馈。高寒草甸的生长季生态系统呼吸和CH4吸收主要受土壤表层5 cm温度的调控,N2O通量主要受到降雨量变化的影响。高寒草甸三种温室气体的平均通量均呈现在生长季中期>后期>前期的趋势,与高寒草甸生态系统呼吸和CH4吸收的土壤温度敏感性在生长季后期大于前期的结果一并,表明高寒草甸碳通量(CO2和CH4)对冻土的冻结过程的敏感性要强于融化过程,即高寒草甸的碳通量对土壤降温过程而非增温过程更加敏感。2. 模拟增温(6.2 °C)显著增强高寒沼泽草甸生态系统呼吸,增幅30.9%;增温促使高寒沼泽草甸由N2O的弱汇转变为弱源,增温对高寒沼泽草甸CH4通量无显著影响。增温和氮沉降增加(与增温处理相比)的交互作用显著促进了高寒沼泽草甸69.6% CH4吸收的和26.2%的N2O排放,但对高寒沼泽草甸生态系统呼吸无显著影响。这与高寒草甸的结果一致,温室气体通量对气候变暖和氮沉降增加同时具有积极和消极的响应。高寒沼泽生态系统呼吸主要受表层土壤温度控制,而土壤水分调控其CH4通量,N2O通量受降水变化的调控。增温对表层土壤温度的影响在生长季前期最强,但增温对生态系统呼吸的促进作用却最弱,表明深层冻土壤起到缓冲温度升高的作用,从而对增温后生态系统呼吸增加产生了削弱作用。通过比较湿地与非湿地温室气体通量之间对气候变化的响应差异,结果表明,虽然湿地生态系统可对气温升高产生缓冲作用,但由于土壤有机碳库较大,生态系统呼吸的温度敏感性较高,其对气候变化的反馈仍不应当被忽视。3. 模拟增温对高寒草甸和高寒沼泽草甸三种温室气体通量特征的影响并未收到降水变化的影响。而氮沉降增加:(1)在相对干旱年份,显著减少了高寒草甸生态系统呼吸;在相对湿润年份,显著降低了高寒沼泽草甸生态系统呼吸;(2)在相对干旱年份,显著增加了高寒草甸CH4吸收,但在相对湿润年份,对高寒草甸CH4通量无显著影响;(3)模拟增温和氮沉降增加在干旱年份对高寒沼泽草甸CH4吸收和N2O排放的交互促进作用,在湿润年份对高寒沼泽草甸生态系统呼吸有显著的相互抵消作用。表明虽然湿地生态系统土壤水分较高,但其温室气体通量对非湿地生态系统的年降水量变化更为敏感。因为干旱放大了氮沉降增加的在非湿地生态系统对碳通量的作用,但在湿地生态系统减弱了这种作用。表明氮沉降增加而非增温对高寒草甸生态系统碳通量(生态系统呼吸 [CO2 ]和CH4)的影响将受到降水变化的影响。4. 模拟碳平衡结果显示,增温促进了典型高寒草甸生态系统生长季日间CO2吸收,增幅约86%;但也促进了其生长季夜间CO2排放(增幅约116%)及其非生长季CO2排放(增幅约12%)。典型高寒草甸是一个碳汇,增温增强典型高寒草甸生态系统的碳贮存能力,增幅约210%。
Other AbstractAlpine meadow is a typical ecosystem of permafrost in the Qinghai-Tibet Plateau (QTP). It not only has important functions of ecosystem services, but also the only means of production of local herders. However, over the past 50 years, the average temperature and annual precipitation of the QTP have increased at a rate of 0.3 °C and 9.1 mm every 10 years. Although the level of nitrogen (N) deposition is less than 2 Kg hm-2 a-1, the N deposition of the QTP showed an increasing trend. These climatic factors will inevitably affect the carbon (C) and N cycles in alpine meadow ecosystem. The greenhouse gas (GHG) flux is an important way to the exchanges of C and N between the biosphere and atmosphere. To investigate the impacts of climate change on the GHG flux is an important part for human understanding of the impact of climate change on C and N cycling in alpine meadow ecosystem. Although the study of GHG flux in alpine ecosystems has been extensively carried out by increasing warming and N deposition, in situ observations about the interaction between warming and N addition have been rare. Especially in the permafrost region, the GHG flux is closely related to the depth of activity and the soil temperature and moisture of the active layer. Additionally, the seasonal variation characteristics of the GHGs in permafrost will probably are different from those of the unfrozen soils. Therefore, GHG flux at different stages of the growing season, which are divided by changes in soil temperature in permafrost regions, are another purpose of this study. In this study, an alpine meadow and an alpine swamp meadow in the Yangtze River source area were selected to investigate the GHG flux (ecosystem respiration [Re], CH4 and N2O) in the early (EG), middle (MG) and late (LG) growing season of two types of alpine meadows. And the effect of future climate change on the change of GHG flux in alpine meadow ecosystem was determined during two contrasting hydrological growing seasons. The main results are as follows:1. warming (4.5 °C) increased the average seasonal Re, CH4 uptake and N2O emission by 73.5%, 65.9% and 431.6%, respectively. N fertilization (4 g N m-2) alone had no significant effect on GHG flux; the interaction of warming and N fertilization enhanced CH4 uptake by 10.3% and N2O emissions by 27.2% than warming, while there was no significant effect on the Re; the average seasonal fluxes of Re, CH4 and N2O were MG>LG>EG, and Re and CH4 uptake were most sensitive to the soil freezing process instead of soil thawing process; surface soil temperature was the main driving factor of the Re and CH4 fluxes, and the N2O flux was mainly affected by daily rainfall; These results indicate that (i) relative to future climate warming (or permafrost thawing), there could be a hysteresis of GHG flux in the alpine meadow of permafrost region; (ii) increasing N deposition has both positive and negative feedbacks on GHG fluxes of alpine meadow in response to climate warming. 2. warming (6.2 °C) increased the average seasonal Re by 30.9% and transformed the alpine swamp meadow from a N2O sink to a source, whereas CH4 flux was not significantly affected. N fertilization (4 g N m-2 a-1) alone had no significant effect on the fluxes of GHGs. The interaction of warming and N fertilization increased CH4 uptake by 69.6% and N2O emissions by 26.2% compared with warming, whereas the Re was not significantly affected. During the EG, although the soil temperature sensitivity of the Re was the highest, the effect of warming on the Re was the weakest. The primary driving factor for Re was soil surface temperature, whereas soil moisture controlled CH4 flux, and the N2O flux was primarily affected by rain events. The results indicated: (i) increasing N deposition has both positive and negative feedbacks on GHG fluxes of alpine swamp meadow in response to climate warming; (ii) during soil thawing process at active layer, low temperature of deep frozen soils have a negative contribution to Re in alpine ecosystems; and (iii) although these alpine wetland ecosystems are buffers against increased temperature, their feedbacks on climate change cannot be ignored because of the large soil organic carbon pool and high temperature sensitivity of the Re.3. warming increased the Re in both the AM and SM, warming increased the CH4 uptake in the AM but had no effect in the SM, and warming increased the N2O emissions from the AM and resulted in a change of the SM from a N2O sink into a source; N fertilization decreased the Re of the AM during the dry growing season and of the SM during the wet growing season, increased the CH4 uptake of the AM during the dry growing season, and had no effect on the CH4 and N2O fluxes of the SM; and the interaction between warming and N fertilization increased the CH4 uptake of the AM over the two growing seasons while increasing the CH4 uptake and N2O emissions of the SM during the dry growing season. Our results suggest that (i) the GHG flux of wetland ecosystems is more sensitive to precipitation variations than that of non-wetlands and (ii) precipitation controls the carbon (Re and CH4) flux response to increasing N deposition of these alpine meadows.4. The results of simulated carbon balance showed that warming promoted the day CO2 uptake of the AM by about 86% during growing season, but also promoted the night CO2 emission by about 116% during the growing season and its non-growing season CO2 emissions increasing by about 12%. The AM is a carbon sink, warming enhanced carbon sequestration of the AM by about 210%. 
Pages97
Language中文
Document Type学位论文
Identifierhttp://ir.imde.ac.cn/handle/131551/24563
Collection山地表生过程与生态调控重点实验室
Affiliation中国科学院成都山地灾害与环境研究所
First Author Affilication中国科学院水利部成都山地灾害与环境研究所
Recommended Citation
GB/T 7714
陈晓鹏. 气候变化对高寒草甸生态系统温室气体通量特征的影响[D]. 北京. 中国科学院大学,2017.
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