【作者】 张峰；

【导师】 李凤民； 齐家国； 李长生；

【作者基本信息】 兰州大学 ， 生态学， 2010， 博士

【摘要】 草原作为我国第二大陆地生态系统,对维持陆地生态系统稳定至关重要。在全球气候变化背景下,草原生态系统的变化动态对区域乃至于全球都会产生影响。温室气体作为全球气候变化的主要原因之一,如何控制其排放量,是人类当前所面临的重要问题之一。作为一个复杂巨系统,生态系统中温室气体的排放又与土壤碳库息息相关。面对如此复杂的生态系统,在未知的气候变化背景下,对生态系统本身有一个清晰的了解,不仅有利于保护当前的生态系统,维持生态系统功能的稳定,而且有利于我们找到生态系统中的脆弱点,因地制宜,建立合理的优化管理措施。在这种背景下,本研究将我国整个草原生态系统作为一个整体进行研究,通过对生态系统中的碳氮循环和水热平衡过程进行追踪,从而获取了中国草原的碳库储量、温室气体的排放量以及二者自2000年以来的变化动态。研究结果表明,草原巨大的碳储量对我国陆地生态系统的稳定有着重要的作用。我国草原生态系统的植被碳库、土壤有机碳库储量分别为2.1 GtC和12.4GtC,总计14.5 GtC。中国草原以占世界8%的面积,储存了7.5%的世界植物碳,4.9%的土壤碳和5%的总碳。同时,根据模拟结果显示,草原目前属于碳汇,其碳库年增加量为71±4 Tg.C.y-1。在我国草原碳库中,高寒草原区域具有最大的碳储量,其次是温性草原区域。其中,高寒草原区域年总碳沉积量可以达到48.26±9.54 Tg,其以占总草原39%的面积沉积了总碳沉积量的68%,具有巨大的固碳能力。尽管草原碳储总量在2000到2007年之间增加了,但是在内蒙古西部的温性荒漠草原、新疆北部的温性和温性荒漠草原以及青藏高原西部的高山草原,碳储量有不同程度的降低趋势。N2O是三类主要温室气体中唯一的非碳化合物温室气体,其温室效应是C02的298倍。目前农业生产活动是N2O增加的主要来源之一。本研究表明,中国各草原类型的N20排放量差异较大,温性草原、高山草原以及热带/亚热带草原的平均排放量分别为0.23 kg N ha-1 y-1,0.11 kg N ha-1 y-1和0.39 kg N ha-1 y-1。在中国33.7亿公顷的草原中,年N2O排放总量为76.5 Gg N,相当于9.71TgCO2-C的温室效应,也即其抵消了约14%的草原碳沉降效果。整个草原区域的N20排放量从2000到2007年有增加的趋势。近年来,中国草原受到人类强烈的扰动,因此未来草原的N20排放模式更应该引起我们的重视。从目前的研究结果来看,尽管草原区域仍然是一个甲烷汇,但是甲烷固定量并不是太大。全国草原甲烷固定量为0.22 Tg CH4-C y-1,相当于1.89 Tg CO2-C。平均甲烷固定通量约为0.95±0.77 Kg C ha-1 y-1,这一结果远小于C02的净沉积率210.62±48.76Kg C ha-1 y-1。由此也可以得出,在草原区域,增加碳汇应该主要以增加C02的固定率,减少N20释放为主。在未来的草原管理中,大面积推广改良草原是增加草原碳库储量并抵消温室气体效应的有效手段。但是在实施过程中,则要根据草原的实际情况来选择适合的改良手段。特别是施肥或灌溉措施的实施,要注意选择合理的阈值,以防止在草原在改良过程中产生大量的温室气体而抵消碳沉积的效果。更多还原

【Abstract】 Grassland, as the second largest terrestrial ecosystem in China, is of crucial importance for the stability of China’s ecosystem. On the background of Global Warming and Climate Change, the dynamic of grassland ecosystem would affect the world more than the local area. How to control the greenhouse gas (GHG) emission has become one of the most important things for human beings due to it’s a main factor contributing the global climate change. Ecosystem is a huge complex system. Meanwhile, the GHG emission is closely linked with the soil carbon pool. Therefore, to obtain a clear comprehension of so complicated ecosystem under unknown climate change background is not only good for the protection of the ecosystem and its stable functions but also good for us to find the weakness of the ecosystem so that we can optimize the management practice accordingly. In this paper, we took the whole grassland ecosystem as our research subject and extracted the carbon sequestration, GHG emission and their interrelations with current agricultural practice of grassland in China by modeling the biogeochemical processes in the ecosystem.The result indicates, as the second largest terrestrial ecosystem, the grassland has a large amount of carbon storage and has been playing an important role in the stability of whole China’s terrestrial ecosystem. The sequestrations of the grassland carbon and the soil organic carbon are 2.1 GtC and 12.4 GtC, respectively. The grassland of China accounts for 8% of the global grassland area and deposits 7.5% of plant carbon,4.9% of soil carbon and 5% of the total carbon, respectively, of the world. The modeled result also indicate that currently the grassland is in a period of carbon sequestration with an increase of 71±4 Tg C y-1, and the large underground carbon pool, which showed quite obviously in alpine steep and alpine meadow, is one significant portion of China grassland carbon storage. A total carbon deposition with 48.26±9.54 per y (68% of total carbon deposition) for montane grassland region, which accounts for 51% of the total grassland area revealed by our research. From this perspective, montane grassland region has a great potential to sequestrate carbon. The total carbon sequestration of grassland increased from 2000 to 2007; however, there was a decrease trend of temperate grassland storage appearing in west of Mongolia, north of Xinjiang and west of Qinghai-Tibetan plateau highland.N2O is the only non-carbohydrate one of 3 main GHG but its global warming potential is 297 times as CO2’s. Current agricultural practice is one main source of N2O increase. N2O emissions in different types of grassland, in China differ from each other. The emissions are 0.23,0.11 and 0.39 kg N ha-1 y-1,respectively for Temperate Grassland, Montane grasslands, Tropical/subtropical grasslands. Grassland in China with a total area of 3.37 billion hectares emitted 76.5 GgN of N2O which equivalent to 9.71 Tg CO2 and counterbalanced 14% of the carbon sequestration of grassland. From 2000 to 2007, a growing tendency appeared for the N2O emission of the whole grassland area. Climate change has played a relative important role on it. Grassland in China suffered an intensive disturbance of human in the last years, which should draw attentions in our future research on the emission mode of N2O of grassland.Although grassland is a methane sink from current research, the amount of sequestration is small with a rate of 226 thousand tons per year. The average methane flux is about 0.95±0.77 Kg C ha-1 y-1 which equivalent to 565 tons of CO2-C and is far smaller than the net sequester rate of CO2 210.62±48.76 Kg C ha-1 y-1. The results suggested that increase the carbon sequestration and reduce N2O emission are priority task in the grassland region.更多还原