NWIPB OpenIR
三江源区退化草地生态系统CO2通量及反射辐射特征的研究
冯 超
学位类型硕士
导师古松
2010-06
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业生态学
关键词退化草地 三江源区 Co2通量 涡度相关法 地表反照率
摘要陆地生态系统的碳收支与能量平衡是全球变化研究中重要的内容之一。青藏高原是世界上海拔最高,高寒草甸分布面积最广的高原。由于自然环境严酷,生态系统十分脆弱,使其对气候变化的响应异常敏感。因此,探讨青藏高原高寒草地生态系统碳收支和能量平衡对区域乃至全球气候变化的影响已成为研究热点。特别是近几十年,由于人为干扰和气候变化等原因,导致草地大面积退化,对生态系统的碳收支状况带来巨大影响。另外,草地退化改变了原有的下垫面特征,对生态系统的能量平衡亦产生影响。因而,研究草地退化对生态系统碳收支及地表反射辐射的影响可为预测高原生态系统碳汇功能以及能量平衡研究提供理论依据,对全面揭示草地退化对区域生态系统的能量收支以及局地气候的影响具有重要意义。 本研究采用微气象方法-涡度相关技术对位于青藏高原腹地的三江源区退化草地生态系统(34°24′N,100°24′E,海拔3958 m)的二氧化碳通量、环境要素及地表反射辐射特征进行了连续观测和研究。该区域属高原寒冷气候类型,生长季降水丰富,辐射资源丰富。本研究利用2006年12月至2007年11月全年的观测数据探讨分析了退化草地的生态系统年CO2净交换(NEE)、总初级生产力(GPP)、生态系统呼吸(Reco)以及Reco /GPP的变化特征以及影响因子,同时分析了该生态系统地表反照率的季节动态和日变化特征及其影响因子。研究结果表明: (1)研究期间三江源区退化草地生态系统CO2年排放量为260.48 gCO2 ·m-2·y-1,总体为一个碳源。年GPP为-1715.03 gCO2 ·m-2·y-1。从6月下旬开始,NEE由正转负,7月30日达到碳吸收的最大值为-9.35 gCO2·m-2·d-1,此后随着生长季的结束NEE逐渐由负转正,生态系统进入碳的净排放期,并在10月初达到第二个排放高峰为7.19 gCO2·m-2·d-1。生长季NEE呈现明显的单峰式变化,在植物生长旺盛的7、8两月生态系统表现为明显的碳汇。
(2)一日中,CO2的最大吸收速率为-0.38 mgCO2·m-2·s-1,最大排放速率为0.25 mgCO2·m-2·s-1,分别出现在7、8月份。生长季晴天状况下NEE的日变化呈现明显的单峰式日变化,一天中碳吸收的高峰时刻出现在上午11:00(北京时)左右,NEE由正变负和由负变正的时间分别在早晨7:00(北京时)和傍晚17:00(北京时)左右。生长季不同时期的NEE日变化具有明显的差异,其中在植物生长旺盛的7、8两月,生态系统的NEE日变化幅度较大。 (3)该生态系统生长季表现出较大的Reco/GPP,其中5和9月的Reco/GPP分别为2.19和1.03都大于1,6-8月的值小于1。生长季平均Reco/GPP为0.95,说明退化草地生态系统呼吸占GPP的比重较大。从上、下午Reco/GPP的情况来看,除5月份以外,下午的Reco/GPP均高于上午。 (4)地表反照率受积雪、云量等环境因子,植被状况等生物因子以及土壤性质的综合影响,呈现出明显的年动态特征。该退化草地生态系统年均地表反照率为0.22,非生长季的平均地表反照率(0.25)高于生长季(0.18)。最高值出现在有积雪覆盖的冬季,最低值出现在降水相对较多、植物生长初期植被覆盖度较低的5月末至6月初。植物生长旺盛的7-8月,地表反照率相对较稳定,并略高于生长季中其它各月。降雪后反照率随积雪的融化呈直线下降趋势。 (5)地表反照率的日变化呈―U‖型,阴天的地表反照率高于晴天。全年地表反照率出现的最大频率集中在0.20附近,非生长季在0.22附近,生长季在0.18附近。 (6)由于该退化草地植被覆盖度低,土壤颜色较暗,降水多,土壤含水量较高,导致该生态系统生长季的地表反照率并未由于草地退化而出现明显增加的趋势。
其他摘要Terrestrial ecosystem carbon cycle and energy balance are important contents of global change study. The Qinghai-Tibetan Plateau is the highest Plateau with the most widely distributed of alpine meadow in the world. Because of its unique geographic and high altitude, the alpine ecosystem in Qinghai-Tibetan Plateau is very fragile and has sensitive responses to global climate change. In the past decades, the area of the grassland in this region has been reduced greatly because of climate warming and human activities. Grassland degradation will results in the change in the ecosystem carbon cycle and energy balance. Therefore, clarifying the carbon dynamics and surface reflection of degraded meadow are essential for understanding the global carbon budget and energy balance and predicts their responses to climate change for the Qinghai-Tibetan Plateau.
Eddy covariance technique and microclimate measurement system were used to measure the CO2 flux and surface reflected radiation at a degraded alpine meadow at the Three-River Source Region in the south of Qinghai province on the Qinghai-Tibetan Plateau, China (Lat 34°24′N, Long 100°24′′E, elevation 3,958 m). The local climate is characterized by strong solar radiation with low temperature and abundant rainfall. The data from December 1, 2006 to November 30, 2007 was used to examine the seasonal and diurnal variations in net ecosystem exchange (NEE), gross primary productivity (GPP), ecosystem respiration (Reco) and albedo of degraded alpine meadow; meanwhile we analyzed the effect of meteorological and biological factors on CO2 exchange. The major results can be summarized as follows: (1) The degraded meadow ecosystem was a carbon source with 260 gCO2·m-2·y-1, and the annual GPP was -1715.03 gCO2·m-2·y-1. Ecosystem became carbon sink from late June and the maximum daytime CO2 uptake with 9.35 gCO2·m-2·d-1 appeared on July 30. After then the magnitude of NEE decreased gradually and become carbon source again in middle of September with the maximum carbon release of 7.19 gCO2·m-2·d-1 in October. (2) The diurnal variation of NEE shows a single peaked pattern under the clear sky conditions with the maximum uptake of -0.38 mgCO2·m-2·s-1 at 11:00 (Beijing time) in July and release of 0.25 mgCO2·m-2·s-1 in August, respectively, during the growing season. It turned to negative at about 7:00 (Beijing time) and positive 17:00 (Beijing time), respectively. The diurnal variation of NEE has obviously difference in different growing period, and the greater variation amplitude occurred in July and August. (3) The larger Reco/GPP appeared in May and September(2.19 and 1.03 respectively) because of the higher ecosystem respiration, and the lower value appeared from June to August. The average ratio of Reco/GPP was 0.95 during the growing season, indicating that Reco has a great contribution to GPP. The ratios of Reco/GPP in afternoon were higher than those in forenoon during the growing season (from May to September) except May. (4) The obviously seasonal variation in albedo was found in this ecosystem due to the effect of environmental and biological factors. The annual average albedo was 0.25, with the average of 0.18 in growing season and 0.25 in non-growing season. The maximum albedo appeared in winter due to the snow cover, and minimum was in the early of growth season when the soil keeps relatively higher water and plants are small. The albedo appeared to remain relatively steady in July and August, which was higher than those in other months of growing season. The albedo decreased linearly with the melting of snow.
(5) The diurnal variation in albedo showed ―U‖ pattern, and the albedo in cloudy skies was higher than that in clear skies. The highest frequency of albedo distributed in about 0.20 for one year, in 0.22 for non-growing season and in 0.18 for growing season, respectively. (6) The results shows that the degraded meadow does not lead to the increase in albedo, the possible reason may be due to the low vegetation coverage, dark-colored soil and high soil water content in this ecosystem during the growing season.
学科领域生物科学
语种中文
文献类型学位论文
条目标识符http://210.75.249.4/handle/363003/3393
专题中国科学院西北高原生物研究所
推荐引用方式
GB/T 7714
冯 超. 三江源区退化草地生态系统CO2通量及反射辐射特征的研究[D]. 北京. 中国科学院研究生院,2010.
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