草地生态系统碳循环及其对全球变化的响应I.碳循环的分室模型、碳输入与贮量

概述了草地生态系统碳素循环的一般特征,介绍了一个草地碳循环的分室模型;对世界草地生态系统的碳贮量和碳输入量的有关数据进行了归纳整理,并初步讨论了草地生态系统在全球碳循环中的作用。     

草地生态系统碳循环及其对全球变化的响应Ⅰ.碳循环的分室模型,碳输 …

概述了草地生态系统碳素循环的一般特征,介绍了一个草地碳循环的分室模型;对世界草地生态系统的碳贮量和碳输入量的有关数据进行了归纳整理,并初步讨论了草地生态系统在全球碳循环中的作用。     

东亚地区碳循环研究新进展

近百年来,温室效应的日益加剧,引发了全球温暖化、海平面上升等一系列重大环境问题,碳循环研究因此而受到全球范围的普遍关注和重视.东亚地区因其独特的气候特征,多样化的物种和生态系统,以及活跃的人类活动而成为世界碳循环研究中不可或缺的一部分.在中、日、韩三国联合启动东亚碳循环前沿研究计划(A3 Foresight Program)三周年之际,《中国科学生命科学》(Science China Life Sciences)2010年第7期发表了东亚地区碳循环研究专题,包括14篇述评和研究论文,从区域碳储量及其变化特征,不同地带森林生态系统的碳源汇变化,草地和农田生态系统的碳储量和碳循环研究中的新方法等多个方面系统展示了东亚地区碳循环研究的最新进展.     

森林生态系统碳循环的基本概念和野外测定方法评述

全球气候变化与森林生态系统碳循环息息相关,定量评估森林碳收支是生态系统与全球变化研究的重要任务。30年来森林生态系统碳循环研究已经取得了长足的进展,但全球和区域森林碳收支仍然存在很大的不确定性。这一方面与森林生态系统本身的复杂性有关,另一方面也与具体研究方法有关。评述了森林生态系统碳循环的基本概念和主要野外测定方法,为我国森林生态系统碳循环研究提供可参考的方法论。从生态系统碳浓度、密度、通量、分配和周转5个方面回顾了碳循环相关概念,指出碳浓度和碳储量是对碳库的静态描述,而碳通量和碳周转是对碳库的动态描述。净初级生产力是测量最普遍的碳通量组分,但大多数情况下因忽略了一些细节而被系统低估。普遍使用的净生态系统生产力,由于没有包含非CO2形式的水文、气象和干扰过程产生的碳通量,通常情况下高于生态系统净碳累积速率。在详细介绍碳通量组分的基础上,改进了森林生态系统碳循环的概念模型。重点讨论了碳通量的3种地面实测方法:测树学方法、箱法和涡度协方差法,并指出了其注意事项和不确定性来源。针对当前碳循环研究的突出问题,建议从4个方面减小碳循环测定的不确定性:(1)恰当运用生物量方程估算乔木生物量;(2)尽可能全面测定生态系统碳组分;(3)给出碳通量估算值的不确定性;(4)多种途径交互验证。     

高原湿地的碳循环

<正>湿地生态系统是陆地生态系统中仅次于森林生态系统的最大碳库,湿地生态系统碳循环在全球碳循环中起着重要作用。湿地独特的水文条件,使得湿地碳循环具有与其他生态系统不同的特点。湿地土壤有机碳的循环过程生态系统有机碳的积累取决于系统植被净初级生产力(NPP)与有机碳分解和净排放之间的差异。湿地植物残体因受湿地多水和还原性强的限制,其分解、转化速度比较缓慢,通常以泥炭或有机质的形式表现为有     

陆地生态系统类型转变与碳循环

 土地利用变化引起的陆地生态系统类型转变对于全球碳循环有着极其重要的作用。　通过总结国内外有关森林砍伐以及森林、草地转变成农田对于碳循环的影响,阐述了可能引起全球“未知汇”现象的重要原因,强调未来中国陆地生态系统碳循环研究应充分重视陆地生态系统类型转变对于全球碳循环的影响研究,包括研究陆地生态系统的不同发展阶段(自然与退化生态系统)、利用方式的改变(森林转化为人工林或农田,草地转化为农田、退耕还林草等)所引起的碳库类型转换的增汇机理及其对全球变化响应,并指出了建立统一观测方法与规范的陆地生态系统碳通量观测网     

土壤溶解性有机碳在陆地生态系统碳循环中的作用

土壤溶解性有机碳(DOC)是有机碳库的活跃组分,在陆地生态系统碳循环中发挥重要作用.本文从碳循环重要性着手,综述了土壤DOC在土壤碳固持与温室气体排放中的作用;结合我国的现实情况(如土壤酸化、气候变暖等),探讨了土壤DOC的相关影响因素如土壤性质、环境因素、人为活动对土壤DOC的影响及作用机制,对进一步理解土壤DOC在陆地生态系统碳循环与温室气体减排中的作用具有重要意义.     

增温增水对草地生态系统碳循环关键过程的影响

生态系统碳循环是生态系统过程的重要组成部分,对碳循环关键过程机理的研究有助于更好地理解生态系统过程。目前,气候变化（全球变暖、降水时空格局变化）对草地生态系统过程产生了重要的影响。综述了气候变化（温度和降水变化）对草地生态系统碳循环关键过程（植物生产力、植物物候、植物根系周转、生态系统呼吸和生态系统净碳交换）的影响,在此基础上指出了目前气候变化（温度和降水变化）控制试验研究的不足,并进一步提出了今后应该加强研究的方向。     

城市土壤碳循环与碳固持研究综述

城市化过程带来的土地利用变化和环境污染是全球变化的重要方面,城市为人们了解人类与自然复合生态系统对全球变化的影响及其对全球变化的响应过程提供一个独特的"天然实验室"。陆地生态系统碳循环是全球变化研究的热点领域之一,然而,人们对城市在全球碳循环中的作用和影响知之甚少,城市土壤碳循环研究处于起步阶段。介绍了城市土壤的主要特性和碳循环特征,指出强烈的人为作用是其最突出的特点;综述了城市土壤碳库、碳通量和碳固持研究方面取得的进展;探讨了城市化过程中土地利用变化、土壤中生物及土壤管护措施、城市小气候、大气污染沉降和土壤污染等对土壤碳循环的影响;提出未来城市碳循环研究需要开展长期系统监测、深化城市土壤碳循环机制研究、创新研究范式和研究方法、并将研究成果与城市景观规划与设计相结合,提升城市土壤碳管理能力。     

DICE/RICE模型中碳循环模块的比较

碳循环模型的正确构建是影响综合集成评估模型IAM(Integrated Assessment Model)模拟结果的重要因素之一。DICE/RICE模型中的碳循环模型主要有两个,即Nordhaus单层碳库模型和Nordhaus三层碳库模型,但这两个模型的主要缺陷是不考虑陆地生态系统在碳循环中的贡献,因此,引入了包含陆地生态系统的Svirezhev碳循环模型,并将其与Nordhaus单层碳库模型、Nordhaus三层碳库模型展开比较研究。结果表明,在基于历史数据的模型检验中,Svirezhev碳循环模型对全球二氧化碳浓度模拟的准确度优于其他两个模型。对于未来全球气候变化的模拟,3个模型模拟得到了至2100年的温度预测值分别为2.98,3.54,2.91℃,二氧化碳浓度值分别为608.04,733.04,594.70μL/L。其中,Svirezhev碳循环模型的模拟值在3个模型中最低,表明了陆地生态系统和海洋对二氧化碳的吸收作用对抑制全球升温的贡献;而分析也发现Nordhaus三层碳库模型对陆地生态系统和海洋碳库的模拟与实际观测值偏离较大。最后,通过敏感性分析,研究发现DICE/RICE模型中使用的气候响应模块在短期温度模拟中对地表温度的初值较为敏感,在长期温度模拟中敏感度显著下降。总之,从碳循环机制的模拟性能而言,Svirezhev碳循环模型优于其他两个模型,而Nordhaus单层碳库模型虽然机制较为简单却保证了模拟的准确性,但Nordhaus三层碳库模型虽然丰富了碳库的表征,实际上各碳库的模拟准确性差,降低了模型的可靠性。     

子午岭林区生态系统转换对土壤有机碳特征的影响

生态系统转换影响土壤有机碳的动态、循环及环境质量.本研究分析了子午岭林区农田、草地、灌丛和森林不同生态系统土壤总有机碳、活性有机碳和稳定性有机碳含量.结果显示:各生态系统中,表层(0~10 cm)土壤总有机碳含量显著高于深层土壤(40~70 cm).与农田生态系统表层土壤相比,草地、灌丛、森林生态系统土壤总有机碳含量分别增加82.07%、121.67%和183.16%,深层土壤有机碳含量也有类似的趋势;从增加的绝对值来看,表层土壤活性有机碳含量分别增加2.24、4.13和5.43 g/kg,土壤稳定性有机碳含量分别增加4.76、6.23和10.18g/kg.表明农田生态系统转换为林、草生态系统,有利于土壤有机碳的积累.而且,土壤作为碳“汇”的功能增强,更有利于CO2固定和生态环境改善.     

Plumbing the Global Carbon Cycle: Integrating Inland Waters into the Terrestrial Carbon Budget

ABSTRACT Because freshwater covers such a small fraction of the Earth’s surface area, inland freshwater ecosystems (particularly lakes, rivers, and reservoirs) have rarely been considered as potentially important quantitative components of the carbon cycle at either global or regional scales. By taking published estimates of gas exchange, sediment accumulation, and carbon transport for a variety of aquatic systems, we have constructed a budget for the role of inland water ecosystems in the global carbon cycle. Our analysis conservatively estimates that inland waters annually receive, from a combination of background and anthropogenically altered sources, on the order of 1.9 Pg C y⁻¹ from the terrestrial landscape, of which about 0.2 is buried in aquatic sediments, at least 0.8 (possibly much more) is returned to the atmosphere as gas exchange while the remaining 0.9 Pg y⁻¹ is delivered to the oceans, roughly equally as inorganic and organic carbon. Thus, roughly twice as much C enters inland aquatic systems from land as is exported from land to the sea. Over prolonged time net carbon fluxes in aquatic systems tend to be greater per unit area than in much of the surrounding land. Although their area is small, these freshwater aquatic systems can affect regional C balances. Further, the inclusion of inland, freshwater ecosystems provides useful insight about the storage, oxidation and transport of terrestrial C, and may warrant a revision of how the modern net C sink on land is described.     

Carbon balance along the Northeast China Transect(NECT-IGBP)

The Northeast China Transect (NECT) along a precipitation gradient wasused to calculate the carbon balance of different vegetation types, land-use practices and temporal scales. NECT consists of mixed coniferous-broadleaved forest ecosystems, meadow steppe ecosystems and typical steppe ecosystems. Analyses of the C budget were carried out with field measurement based on dark enclosed chamber techniques and alkali absorption methods, and the application of the CENTURY model. Results indicated that: (1) soil CO2 flux had a strong diurnal and seasonal variation influenced by grassland type and land-use practices. However, the seasonal variation on soil CO2 fluxes did not show obvious changes between non-grazing and grazing Leymus chinensis dominated grasslands. (2) Hourly soil CO2 fluxes mainly depended on temperature, while daily CO2 fluxes were affected bothby temperature and moisture. (3) NPP of the three typical ecosystems showed linear relationships with inter-annual precipitation, but total soil carbon of those ecosystems did not. NPP and total soil carbon values decreased westward with decreasing precipitation. (4) Model simulation of NPP and total soil carbon showed that mean annual precipitation was the major limiting factor for ecosystem productivity along NECT. (5) Mean annual carbon budget is the largest for the mixedconiferous- broadleaved forest ecosystem (503.2 gC m-2 a-1), followed by the meadow steppe ecosystem (227.1 gC m-2 a-1), and the lowest being the typical steppe ecosystem (175.8 gC m-2 a-1). This study shows that concurrent field measurements of terrestrial ecosystems including the soil and plant systems with surface layer measurements along the water-driven IGBP-NECT are valuable in understanding the mechanisms driving the carbon cycle in different vegetation types under different land-use practices. Future transect research should be emphasized.     

Land Use Alters the Drought Responses of Productivity and CO<Subscript>2</Subscript> Fluxes in Mountain Grassland

Climate extremes and land-use changes can have major impacts on the carbon cycle of ecosystems. Their combined effects have rarely been tested. We studied whether and how the abandonment of traditionally managed mountain grassland changes the resilience of carbon dynamics to drought. In an in situ common garden experiment located in a subalpine meadow in the Austrian Central Alps, we exposed intact ecosystem monoliths from a managed and an abandoned mountain grassland to an experimental early-summer drought and measured the responses of gross primary productivity, ecosystem respiration, phytomass and its components, and of leaf area index during the drought and the subsequent recovery period. Across all these parameters, the managed grassland was more strongly affected by drought and recovered faster than the abandoned grassland. A bivariate representation of resilience confirmed an inverse relationship of resistance and recovery; thus, low resistance was related to high recovery from drought and vice versa. In consequence, the overall perturbation of the carbon cycle caused by drought was larger in the managed than the abandoned grassland. The faster recovery of carbon dynamics from drought in the managed grassland was associated with a significantly higher uptake of nitrogen from soil. Furthermore, in both grasslands leaf nitrogen concentrations were enhanced after drought and likely reflected drought-induced increases in nitrogen availability. Our study shows that ongoing and future land-use changes have the potential to profoundly alter the impacts of climate extremes on grassland carbon dynamics.     

Carbon dioxide consumption during soil development

Carbon is sequestered in soils by accumulation of recalcitrant organic matter and by bicarbonate weathering of silicate minerals. Carbon fixation by ecosystems helps drive weathering processes in soils and that in turn diverts carbon from annual photosynthesis-soil respiration cycling into the long-term geological carbon cycle. To quantify rates of carbon transfer during soil development in moist temperate grassland and desert scrubland ecosystems, we measured organic and inorganic residues derived from the interaction of soil biota and silicate mineral weathering for twenty-two soil profiles in arkosic sediments of differing ages. In moist temperate grasslands, net annual removal of carbon from the atmosphere by organic carbon accumulation and silicate weathering ranges from about 8.5 g m^–2 yr^–1 for young soils to 0.7 g M^–2 yr^–1 for old soils. In desert scrublands, net annual carbon removal is about 0.2 g m^–2 yr^–1 for young soils and 0.01 g m^–2 yr^–1 for old soils. In soils of both ecosystems, organic carbon accumulation exceeds CO₂ removal by weathering, however, as soils age, rates of CO₂ consumption by weathering accounts for greater amounts of carbon sequestration, increasing from 2% to 8% in the grassland soils and from 2% to 40% in the scrubland soils. In soils of desert scrublands, carbonate accumulation far outstrips organic carbon accumulation, but about 90% of this mass is derived from aerosolic sources that do not contribute to long-term sequestration of atmospheric carbon dioxide.     

Warming Reduces Carbon Losses from Grassland Exposed to Elevated Atmospheric Carbon Dioxide

The flux of carbon dioxide (CO₂) between terrestrial ecosystems and the atmosphere may ameliorate or exacerbate climate change, depending on the relative responses of ecosystem photosynthesis and respiration to warming temperatures, rising atmospheric CO₂, and altered precipitation. The combined effect of these global change factors is especially uncertain because of their potential for interactions and indirectly mediated conditions such as soil moisture. Here, we present observations of CO₂ fluxes from a multi-factor experiment in semi-arid grassland that suggests a potentially strong climate – carbon cycle feedback under combined elevated [CO₂] and warming. Elevated [CO₂] alone, and in combination with warming, enhanced ecosystem respiration to a greater extent than photosynthesis, resulting in net C loss over four years. The effect of warming was to reduce respiration especially during years of below-average precipitation, by partially offsetting the effect of elevated [CO₂] on soil moisture and C cycling. Carbon losses were explained partly by stimulated decomposition of soil organic matter with elevated [CO₂]. The climate – carbon cycle feedback observed in this semiarid grassland was mediated by soil water content, which was reduced by warming and increased by elevated [CO₂]. Ecosystem models should incorporate direct and indirect effects of climate change on soil water content in order to accurately predict terrestrial feedbacks and long-term storage of C in soil.     

早春和夏季氮磷添加对内蒙古典型草原退化群落碳交换的影响

过度放牧导致的养分“入不敷出”是我国天然草地大面积退化的主要原因之一, 而草地退化又显著影响了草原生态系统的固碳功能。能否通过补充土壤养分来恢复退化草地的固碳功能, 迄今相关研究较少。净生态系统碳交换(NEE)、生态系统呼吸(ER)和生态系统总初级生产力(GEP)是表征生态系统碳循环的重要指标。氮(N)和磷(P)是中国典型草原的主要限制性养分元素, 而草地退化进一步加剧了养分的限制。在退化草地上添加氮磷对碳循环的上述过程(NEE、ER和GEP)有何影响, 以及两种养分之间是否存在互作, 目前尚不清楚。为此, 该研究以内蒙古典型草原的退化草地为研究对象, 选择早春融雪期(4月)和夏季生长期(7月)两个时间节点, 设置不施肥(CK)、N添加(10.5 g·m^-2·a^-1, NH₄NO₃)、P添加(7 g·m^-2·a^-1, KH₂PO₄)和N、P共同添加((10.5 g N + 7 g P)·m^-2·a^-1) 4个养分处理, 探究早春和夏季氮磷添加对内蒙古典型草原退化群落碳交换的影响及其互作机制。结果表明: 1)在早春和夏季两个时期, 单独添加N或P对生态系统碳交换过程的影响均未达到显著水平, 而氮磷共同添加可显著提高NEE和GEP。2)早春(4月份)氮磷共同添加对NEE、ER和GEP的互作机制表现为正协同效应, 而夏季(7月份)氮磷共同添加对NEE、ER和GEP的互作机制表现为加性效应。为了恢复退化的典型草原的固碳功能, 氮磷共同添加比单一元素添加效果好, 且早春添加优于夏季添加。该研究对指导退化草地的恢复具有参考价值。     

Precipitation Pattern Determines the Inter-annual Variation of Herbaceous Layer and Carbon Fluxes in a Phreatophyte-Dominated Desert Ecosystem

Arid and semi-arid ecosystems dominated by shrubby species are an important component in the global carbon cycle but are largely under-represented in studies of the effect of climate change on carbon flux. This study synthesizes data from long-term eddy covariance measurements and experiments to assess how changes in ecosystem composition, driven by precipitation patterns, affect inter-annual variability of carbon flux and their components in a halophyte desert community dominated by deep-rooted shrubs (phreatophytes, which depend on groundwater as their primary water source). Our results demonstrated that the carbon balance of this community responded strongly to precipitation variations. Both pre-growing season precipitation and growing season precipitation frequency significantly affected inter-annual variations in ecosystem carbon flux. Heavy pre-growing season precipitation (November–April, mostly as snow) increased annual net ecosystem carbon exchange, by facilitating the growth and carbon assimilation of shallow-rooted annual plants, which used spring and summer precipitation to increase community productivity. Sufficient pre-growing season precipitation led to more germination and growth of shallow-rooted annual plants. When followed by high-frequency growing season precipitation, community productivity of this desert ecosystem was lifted to the level of grassland or forest ecosystems. The long-term observations and experimental results confirmed that precipitation patterns and the herbaceous component were dominant drivers of the carbon dynamics in this phreatophyte-dominated desert ecosystem. This study illustrates the importance of inter-annual variations in climate and ecosystem composition for the carbon flux in arid and semi-arid ecosystems. It also highlights the important effect of changing frequency and seasonal pattern of precipitation on the regional and global carbon cycle in the coming decades.