森林生态系统碳储量及碳通量遥感监测研究进展

在全球CO₂浓度持续增加导致气候变暖的背景下,森林生态系统碳储量及碳通量遥感大尺度监测成为关注热点。文中深入分析了当前国内外卫星遥感观测技术对森林碳循环评估的2种途径:1）基于遥感手段估算森林生物量并推算森林碳储量,通过碳储量变化确定森林生态系统的CO₂通量。归纳各类森林生物量遥感估算方法的原理及优缺点,系统评述各类方法在大区域森林碳储量估算中存在的不确定性。2）基于CO₂温室气体观测卫星遥感数据,定量监测森林生态系统与大气CO₂通量,基于交换的CO₂通量推算森林碳储量变化。归纳遥感手段观测森林生态系统与大气CO₂通量的主要数据、方法及优缺点,系统评述各类数据及方法在森林CO₂通量时空变化特征监测、森林碳储量估算等方面取得的进展,重点分析专用CO₂浓度监测卫星数据,尤其是我国自主碳卫星数据在CO₂柱浓度反演算法研究以及不同数据源之间的对比、验证和同化研究等方面取得的进展,总结专用温室气体遥感观测数据在森林碳储量及碳通量监测方面的优势。提出利用遥感手段进行森林生态系统碳循环定量监测的研究展望。     

森林生态系统碳通量遥感估算中若干问题的探讨

森林生态系统碳通量是判定森林是CO₂源/汇的标准, 其准确估算对碳循环研究具有重要的意义。针对森林生态系统碳通量的遥感研究处于起步阶段, 还有很多问题值得我们去探索。文中较系统地总结了有关碳通量的3种主要研究方法——样地清查法、通量观测法和模型模拟法; 重点分析了碳通量遥感估算中存在的问题, 主要有模型的全遥感化、尺度扩展和模型的不确定性等, 并对如何解决这些问题提出了粗浅的看法, 展望了一个全遥感化的森林生态系统碳通量模型, 希望对相关研究的开展有一些促进作用。     

森林固碳能力估测方法及其研究进展

综述了全球范围内森林生态系统碳平衡估测的2种主要方法,即测定表面通量的微气象学方法(涡旋相关法)和生物量清单统计方法。指出了每种方法的优缺点及综合运用各种方法的重要性。简要介绍了应用上述方法对森林生态系统碳平衡研究的进展情况,并对今后森林生态系统碳平衡研究的发展趋势进行了探讨。     

环境同位素在森林生态系统水循环研究中的应用

环境同位素技术有较高的灵敏度与准确性, 为水循环研究提供了新的技术手段。文中综述了环境同位素概念、示踪原理及其在生态系统水循环过程, 包括大气降水、林冠穿透水、地表水、土壤水、地下水和植物水过程的应用现状, 同时展望了环境同位素在定量阐明森林生态系统"六水"转化关系和水循环机理研究中的应用前景。     

稳定同位素技术在森林生态系统碳水循环中的应用

碳水循环是森林生态系统养分循环的重要组成部分,稳定同位素技术因其准确、安全、灵敏等特点被广泛应用于生态、环境、林业等众多研究领域,已逐步成为了解森林生态系统养分循环的强有力工具.近年来,稳定同位素技术在构建森林生态系统碳水耦合模型、计算水分利用效率、量化植被蒸腾和土壤蒸发对森林蒸散量的贡献等方面研究较多.通过论述森林生...     

森林生态系统碳通量研究进展

陆地生态系统是"温室气体"的一个主要排放源, 森林生态系统作为陆地生态系统最大的碳库, 研究其系统与大气界面的碳通量变化具有重要的科研和社会意义。文中简述了森林生态系统碳通量研究的意义和进展, 以及存在的问题和解决途径。     

森林固碳领域的研究方法及最新进展

介绍了样地清查法、微气象学方法、地面同位素方法、应用遥感等新技术模型估算法四大类森林固碳研究方法及其研究现状,分析了各种方法的优势与不足,并指出森林生态系统碳储量的研究将朝着多种方法的综合运用、多学科的联合和渗透方向发展,对碳储量的估算应更加注重多种因素的综合影响,并能在一定程度上揭示碳储量的动态变化过程及其变化机理。     

森林生态系统碳蓄积研究方法进展

作为陆地生态系统的主体,森林生态系统的碳循环与碳蓄积对研究陆地生态系统碳循环起着重要作用.生物量、生产力、土壤有机质以及凋落物量及其分解等相互关系决定了森林生态系统的碳库量和碳交换量.本文简单地介绍了在碳蓄积研究中森林生物量和生产力的几种研究方法,并对研究过程中的问题(大尺度生物量的精确估算,地下生物量的研究,森林生态系统土壤碳库估算)进行了探讨.     

样地清查法在森林碳汇估算中的应用进展

森林是陆地生态系统的重要组成部分,在全球碳循环中起到重要的作用。森林固定的碳每年约占整个陆地生态系统的2/3,其变化决定了陆地生态系统碳源和碳汇的功能。目前,国内外众多学者对区域尺度森林碳储量的估算所提出的方法较多,但还没有统一的估算方法。样地查清法是估算森林碳储量的方法之一,通过总结该方法的优缺点及应用范围,为碳储量估算精度和碳评估提供合理的参考。     

碳氢氧稳定同位素在草地生态系统水循环研究中的应用

碳氢氧稳定同位素是存在于天然水体和植物组织中的良好的示踪剂,具有较高的灵敏度与准确性,可系统和定量地阐明草地生态系统水循环过程及各水体的转化关系、植物水分利用策略以及植被对全球变化的响应机制等。本文概述了稳定同位素的基本概念和原理,总结和分析了草地生态系统水循环的研究方法和现状,重点探讨和综述了氢氧稳定同位素技术在草地生态系统水循环过程(包括大气降水、地表水、土壤水、地下水、植物水、蒸发水等)以及碳稳定同位素技术在植物水分利用效率中应用的国内外研究进展,分析了其存在的问题,展望了这一领域未来的研究方向和应用前景,为我国草地资源保护、合理利用及退化草地生态系统恢复等提供理论依据。     

安庆杨树林生态系统碳通量及其影响因子研究

以安徽安庆长江外滩地杨树林生态系统为研究对象,运用涡度相关技术进行长期CO2通量监测,得到2005年4月到2006年3月间生态系统碳通量的日动态变化过程:从7:30左右生态系统开始吸收CO2,午间13:30左右达到全天碳吸收最高峰,然后开始降低,到17:30左右生态系统逐渐转入碳排放;同时分析了生态系统碳通量与光合有效辐射(PAR)、温度、土壤热通量等环境因子的响应变化关系:PAR＞1 μmol·m-2·s-1时,在不同温度范嗣内,PAR与碳通量的响应关系不同;平均夜间碳通量与月平均气温呈线性相关;平均夜间碳通量与5 cm处土壤日平均温度呈指数相关;月平均碳通量与2 cm深处土壤热通量也呈指数相关.     

Environmental controls on the carbon isotope composition of ecosystem-respired CO2 in contrasting forest ecosystems in Canada and the USA

We compared the carbon isotope composition of ecosystem-respired CO2 (delta13C(R)) from 11 forest ecosystems in Canada and the USA and examined differences among forest delta13C(R) responses to seasonal variations in environmental conditions from May to October 2004. Our experimental approach was based on the assumption that variation in delta13C(R) is a good proxy for short-term changes in photosynthetic discrimination and associated shifts in the integrated ecosystem-level intercellular to ambient CO2 ratio (c(i)/c(a)). We compared delta13C(R) responses for three functional groups: deciduous, boreal and coastal forests. The delta13C(R) values were well predicted for each group and the highest R2 values determined for the coastal, deciduous and boreal groups were 0.81, 0.80 and 0.56, respectively. Consistent with previous studies, the highest correlations between delta13C(R) and changes in environmental conditions were achieved when the environmental variables were averaged for 2, 3 or 4 days before delta13C(R) sample collection. The relationships between delta13C(R) and environmental conditions were consistent with leaf-level responses, and were most apparent within functional groups, providing support for our approach. However, there were differences among groups in the strength or significance, or both, of the relationships between delta13C(R) and some environmental factors. For example, vapor pressure deficit (VPD) and soil temperature were significant determinants of variation in delta13C(R) in the boreal group, whereas photosynthetic photon flux (PPF) was not; however, in the coastal group, variation in delta13C(R) was strongly correlated with changes in PPF, and there was no significant relationship with VPD. At a single site, comparisons between our delta13C(R) measurements in 2004 and published values suggested the potential application of delta13C(R) measurements to assess year-to-year variation in ecosystem physiological responses to changing environmental conditions, but showed that, in such an analysis, all environmental factors influencing carbon isotope discrimination during photosynthetic gas exchange must be considered.     

No diurnal variation in rate or carbon isotope composition of soil respiration in a boreal forest

Characterization of soil respiration rates and delta(13)C values of soil-respired CO(2) are often based on measurements at a particular time of day. A study by Gower et al. (2001) in a boreal forest demonstrated diurnal patterns of soil CO(2) flux using transparent measurement chambers that included the understory vegetation. It is unclear whether these diurnal patterns were solely the result of photosynthetic CO(2) uptake during the day by the understory or whether there were underlying trends in soil respiration, perhaps driven by plant root allocation, as recently demonstrated in Mediterranean oak savannah. We undertook intensive sampling campaigns in a boreal Picea abies L. Karst. forest to investigate whether diurnal variations in soil respiration rate and stable carbon isotope ratio (delta(13)C) exist in this ecosystem when no understory vegetation is present in the measurement chamber. Soil respiration rates and delta(13)C were measured on plots in which trees were either girdled (to terminate the fraction of soil respiration directly dependent on recent photosynthate from the trees), or not girdled, every 4 h over two 48-hour cycles during the growth season of 2004. Shoot photosynthesis and environmental parameters were measured concurrently. No diurnal patterns in soil respiration rates and delta(13)C were observed in either treatment, despite substantial variations in climatic conditions and shoot photosynthetic rates in non-girdled trees. Consequently, assessment of daily soil respiration rates and delta(13)C in boreal forest systems by single, instantaneous daily measurements does not appear to be confounded by substantial diurnal variation.     

Daily and seasonal patterns of carbon and water fluxes above a north Australian savanna

Daily and seasonal fluxes of carbon dioxide and water vapor above a north Australian savanna were recorded over a complete dry season-wet season annual cycle using the eddy covariance technique. Wet season rates of photosynthesis and transpiration were larger than those measured in the dry season and were dominated by the presence of the grassy understory. As the dry season progressed and the grass understory died, ecosystem rates of assimilation and water vapor flux declined substantially. By the end of the dry season, canopy assimilation and evapotranspiration rates were 20-25% of wet season values. Assimilation was light saturated in the dry season but not in the wet season. Stomatal control of transpiration increased between the wet and dry season. This was revealed by the decline in the slope of E with increasing leaf-to-air vapor pressure difference (D) between wet and dry seasons, and also by the significant decrease in the ratio of boundary to canopy conductance observed between the wet and dry seasons. A simple pan-tropical modeling of leaf area index or wet season canopy CO2 flux was undertaken. It was shown that with readily available data for foliar N content and the ratio of rainfall to potential evaporation, leaf index and wet season canopy CO2 flux can be successfully estimated for a number of tropical ecosystems, including north Australian savannas.     

Estimating CO(2) flux from snowpacks at three sites in the Rocky Mountains

Soil surface CO(2) flux (F(s)) is the dominant respiratory flux in many temperate forest ecosystems. Snowpacks increase this dominance by insulating the soil against the low temperature to which aboveground components are exposed. However, measurement of F(s) in winter may be impeded by snow cover. Likewise, developing annual F(s) models is complicated by seasonal variation in root and microbial metabolism. We compared three methods of measuring sub-snow F(s): (1) dynamic chamber measurements at the upper snowpack surface (F(snow)), (2) dynamic chamber measurements at the soil surface via snowpits (F(soil)), and (3) static estimates based on measured concentrations of carbon dioxide ([CO(2)]) and conductance properties of the snowpack (F(diffusional)). Methods were compared at a mid-elevation forest in northeastern Washington, a mid-elevation forest in northern Idaho, and a high-elevation forest and neighboring meadow in Wyoming. The methods that minimized snowpack disturbance, F(diffusional) and F(snow), yielded similar estimates of F(s). In contrast, F(soil) yielded rates two to three times higher than F(snow) at the forested sites, and seven times higher at the subalpine meadow. The ratio F(soil)/F(snow) increased with increasing snow depth when compared across all sites. Snow removal appears to induce elevated soil flux as a result of lateral CO(2) diffusion into the pit. We chose F(snow) as our preferred method and used it to estimate annual CO(2) fluxes. The snowpack was present for 36% of the year at this site, during which time 132 g C m(-2), or 17% of the annual flux, occurred. We conclude that snowpack CO(2) flux is quantitatively important in annual carbon budgets for these forests and that the static and dynamic methods yield similar and reasonable estimates of the flux, as long as snowpack disturbance is minimized.     

半干旱区农田和草地与大气间二氧化碳和水热通量的模拟研究

集成生物圈模型（IBIS）是目前最复杂的基于动态植被模型的陆面生物物理模型之一.应用该模型对国际CEOP计划半干旱区基准站之一的吉林通榆观测站（44°25＇N , 122°52＇E）草地和农田生态系统2003年全年的CO2和水、热通量变化进行模拟,并将结果与涡度相关法测定的观测值进行了对比分析,以检验IBIS模型在半干旱区的模拟能力.对比结果表明：除CO2通量模拟结果不够理想外,IBIS模型较好地模拟了通榆观测站的感热通量和潜热通量.总体上看,该模型对农田生态系统模拟的偏差小于对退化草地的模拟.     

High-frequency analysis of the complex linkage between soil CO(2) fluxes, photosynthesis and environmental variables

High-frequency soil CO(2) flux data are valuable for providing new insights into the processes of soil CO(2) production. A record of hourly soil CO(2) fluxes from a semi-arid ponderosa pine stand was spatially and temporally deconstructed in attempts to determine if variation could be explained by logical drivers using (i) CO(2) production depths, (ii) relationships and lags between fluxes and soil temperatures, or (iii) the role of canopy assimilation in soil CO(2) flux variation. Relationships between temperature and soil fluxes were difficult to establish at the hourly scale because diel cycles of soil fluxes varied seasonally, with the peak of flux rates occurring later in the day as soil water content decreased. Using a simple heat transport/gas diffusion model to estimate the time and depth of CO(2) flux production, we determined that the variation in diel soil CO(2) flux patterns could not be explained by changes in diffusion rates or production from deeper soil profiles. We tested for the effect of gross ecosystem productivity (GEP) by minimizing soil flux covariance with temperature and moisture using only data from discrete bins of environmental conditions (±1 °C soil temperature at multiple depths, precipitation-free periods and stable soil moisture). Gross ecosystem productivity was identified as a possible driver of variability at the hourly scale during the growing season, with multiple lags between ~5, 15 and 23 days. Additionally, the chamber-specific lags between GEP and soil CO(2) fluxes appeared to relate to combined path length for carbon flow (top of tree to chamber center). In this sparse and heterogeneous forested system, the potential link between CO(2) assimilation and soil CO(2) flux may be quite variable both temporally and spatially. For model applications, it is important to note that soil CO(2) fluxes are influenced by many biophysical factors, which may confound or obscure relationships with logical environmental drivers and act at multiple temporal and spatial scales; therefore, caution is needed when attributing soil CO(2) fluxes to covariates like temperature, moisture and GEP.     

Seasonal dynamics of water use efficiency of typical forest and grassland ecosystems in China

We selected four sites of ChinaFLUX representing four major ecosystem types in China—Changbaishan temperate broad-leaved Korean pine mixed forest (CBS), Dinghushan subtropical evergreen broadleaved forest (DHS), Inner Mongolia temperate steppe (NM), and Haibei alpine shrub-meadow (HBGC)—to study the seasonal dynamics of ecosystem water use efficiency (WUE = GPP/ET, where GPP is gross primary productivity and ET is evapotranspiration) and factors affecting it. Our seasonal dynamics results indicated single-peak variation of WUE in CBS, NM, and HBGC, which were affected by air temperature (Ta) and leaf area index (LAI), through their effects on the partitioning of evapotranspiration (ET) into transpiration (T) (i.e., T/ET). In DHS, WUE was higher at the beginning and the end of the year, and minimum in summer. Ta and soil water content affected the seasonal dynamics of WUE through their effects on GPP/T. Our results indicate that seasonal dynamics of WUE were different because factors affecting the seasonal dynamics and their mechanism were different among the key ecosystems.     

湖南会同杉木人工林生态系统CO_2通量特征

利用开路式涡动相关系统与自动气象梯度观测系统2008年12个月的观测数据,研究会同13年生杉木人工林CO2通量特征。结果表明:13年生杉木人工林生态系统CO2通量日变化存在明显的季节差异,晴天平均碳汇持续时间表现为夏>春>秋>冬,平均日较差表现为夏>秋>春>冬,最大碳汇出现时间由早到晚依次为夏、秋、春和冬;1年中,月累积碳通量除1和2月为碳源外,其他各月均表现为碳汇,碳汇最大值出现在6月(-53.0gC·m-2);13年生杉木林的年碳汇总量为-255.3gC·m-2。白天CO2通量与光合有效辐射的关系可用Michaelis-Menten模型模拟(P<0.05),但模型参数随温度而异;夜间CO2通量与5cm土壤温度呈指数关系(P<0.05)。     

Ecosystem-scale biosphere-atmosphere interactions of a hemiboreal mixed forest stand at Järvselja, Estonia

During two measurement campaigns, from August to September 2008 and 2009, we quantified the major ecosystem fluxes in a hemiboreal forest ecosystem in Järvselja, Estonia. The main aim of this study was to separate the ecosystem flux components and gain insight into the performance of a multi-species multi-layered tree stand. Carbon dioxide and water vapor fluxes were measured using the eddy covariance method above and below the canopy in conjunction with the microclimate. Leaf and soil contributions were quantified separately by cuvette and chamber measurements, including fluxes of carbon dioxide, water vapor, nitrogen oxides, nitrous oxide, methane, ozone, sulfur dioxide, and biogenic volatile organic compounds (isoprene and monoterpenes). The latter have been as well characterized for monoterpenes in detail. Based on measured atmospheric trace gas concentrations, the flux tower site can be characterized as remote and rural with low anthropogenic disturbances.Our results presented here encourage future experimental efforts to be directed towards year round integrated biosphere-atmosphere measurements and development of process-oriented models of forest-atmosphere exchange taking the special case of a multi-layered and multi-species tree stand into account. As climate change likely leads to spatial extension of hemiboreal forest ecosystems a deep understanding of the processes and interactions therein is needed to foster management and mitigation strategies.