地表水热通量研究进展

介绍了当前国内外地表水热通景观测研究的进展及3种不同类型的土壤-植被-大气传输模型（SVAT）：单层模型、双层模型和多层模型。遥感手段常用于监测大面积地表水热通量。基于地表能量平衡方程,现已建立了许多遥感模型以估算水热通量（如简化模型、单层模型、附加阻抗模型、作物缺水指数模型和二源阻抗模型等）,并对这些模型复杂程度及应用范围进行了分析。     

用光合-蒸散耦合模型模拟冬小麦CO2通量的日变化

根据SPAC理论建立了一个冬小麦光合和蒸散的耦合模型.冬小麦CO2通量包括冠层光合、呼吸和土壤呼吸.冠层光合采用了Farquhar光合作用生化模型,并通过冠层阻力的参数化将光合作用与蒸腾作用耦合起来.用涡度相关方法观测了CO2通量,对模型进行了验证,结果显示模型可以较好地模拟CO2通量日变化过程.对模型的敏感性分析发现日间CO2通量最敏感的参数是初始量子效率.其次,CO2通量对光响应曲线凸度、CO2补偿点、凋萎点和叶面积指数的变化也有着较强的敏感性;夜间CO2通量敏感的参数是最适温度下Rubisco催化能力和暗呼吸参数.     

植被-大气相互作用中的气孔导度及其尺度转换

气孔导度是衡量植物和大气间水分、能量及CO2平衡和循环的重要指标,探讨气孔导度在叶片、冠层及区域尺度间的尺度转换及累积效应,对更好地认识植被与大气间的水热运移过程,合理评价植被在陆面过程中的地位和作用具有重要意义.本文着重从叶片尺度气孔导度模拟、气孔导度在冠层尺度的累积表现、冠层到区域尺度转换研究及气孔导度累积效应在陆面过程模型中的作用等4个层次总结了近期国内外研究状况,指出其中存在的异质性等问题,并就今后应加强多尺度间的同步观测提出了展望.     

基于不同浓度变量的温带落叶阔叶林CO2储存通量的误差分析

利用帽儿山温带落叶阔叶林通量塔8层CO2/H2O浓度廓线的测定数据,比较分析了基于不同浓度变量[密度(ρc)、摩尔分数(cc)和混合比(χc)]计算CO2储存通量(Fs)的误差.结果表明:通量观测的控制体积内部干空气储存量不为常数,其波动可引起CO2分子进出控制体积,即干空气储存通量调整项(Fsd)的变化.在夜间以及昼夜转换期,Fsd相对于涡动通量而言较大,忽略Fsd将为森林与大气之间净CO2交换量的计算带来误差.大气水热过程对Fs计算引起的误差包括3方面:空气温度变化引起的误差最大,比大气压强(P)的影响高1个数量级;水蒸气的影响在温暖湿润的夏季大于P的影响,但在寒冷干燥的冬季则相反;P的效应在全年均较低.基于ρc、cc和χc计算Fs分别平均高估CO2有效储存通量(Fs_E)8.5%、0.6%和0.1%.在通量计算过程中,建议选择对大气水热过程守恒的χc计算Fs.     

用光合-蒸散耦合模型模拟冬小麦CO2通量的日变化

根据 SPAC理论建立了一个冬小麦光合和蒸散的耦合模型。冬小麦 CO2 通量包括冠层光合、呼吸和土壤呼吸。冠层光合采用了 Farquhar光合作用生化模型 ,并通过冠层阻力的参数化将光合作用与蒸腾作用耦合起来。用涡度相关方法观测了 CO2通量 ,对模型进行了验证 ,结果显示模型可以较好地模拟 CO2 通量日变化过程。对模型的敏感性分析发现日间 CO2 通量最敏感的参数是初始量子效率。其次 ,CO2 通量对光响应曲线凸度、CO2 补偿点、凋萎点和叶面积指数的变化也有着较强的敏感性 ;夜间 CO2 通量敏感的参数是最适温度下 Rubisco催化能力和暗呼吸参数     

用GSVAT模型研究地表/大气界面传输

用麦男水分和能量平衡资料验证了包括地下水的土壤－植被－大气水热传输模型（ＧＳＶＡＴ）,结果显示,模型能较好地模拟地表／大气水热传输特征,以及土壤水分的动态变化。通过敏感性分析,探讨叶／气界面,土壤／空气界面的节水调控效应,结果发现这两个界面对水汽传输的交互影响显著,若同时增加它们的水汽传输阻力,节水效果尤其明显。     

气候变化对长白山阔叶红松林冠层蒸腾影响的模拟

应用基于过程的碳水耦合多层模型对长白山阔叶红松林冠层蒸腾量进行了模拟和模型验证,并模拟了冠层蒸腾量对未来气候变化的响应.结果表明:多层模型可以较好地模拟长白山阔叶红松林冠层蒸腾量,模拟值与涡动相关技术观测的实测值拟合较好.冠层蒸腾对气候变化响应的模拟显示,气温升高,潜热通量(LE)增加;土壤含水量减少,LE减少;大气CO2浓度增加,LE减少.在研究假定的气候变化情景下,LE对0～20 cm土壤含水量减少10%、CO2浓度增加190μmol·mol-1的联合变化的响应最敏感,对气温增加3.6℃、土壤含水量减少10%的联合变化的响应不敏感.     

黄河小浪底人工混交林冠层CO2储存通量变化特征

基于黄河小浪底人工混交林2008年的CO2浓度和碳通量数据,分析了不同天气条件下CO2浓度在时间和空间上的变化特征,对比了CO2浓度廓线法和涡度相关法估算的CO2储存通量,研究了CO2储存通量的日、季变化特征。结果表明:人工混交林冠层上方月平均CO2浓度具有明显的季节变化规律。月平均CO2浓度最大值出现在3月(370μmol/mol),最低值出现在8月(347μmol/mol)。涡度相关法估算的CO2储存通量比廓线法所得结果偏低9%。生长季,冠层CO2储存通量和净生态系统碳交换量(NEE)日平均值分别为-0.0004和-0.091 mg CO2m-2s-1,冠层CO2储存通量在NEE中仅占0.4%。2008年CO2储存通量和NEE分别为-46.1、-1133 g CO2m-2a-1。在年尺度上,CO2储存通量占NEE的4.1%。因此,在日和年尺度上计算黄河小浪底人工混交林NEE时,CO2储存通量可以忽略。     

生态系统模拟模型的研究进展

从四个方面概述了生态系统模拟模型的发展现状：1)个体及种群,种群动态模型主要模拟在一个生境中单个种的动、植物个体出生或发芽、成长及其死亡过程,还有种内竞争和种间相互作用,主要分析生境中生物之间的相互作用。主要概述了林窗模型和土壤一植物一大气系统模型。2)群落与生态系统,概述了生态系统生产力模型、生物地球化学循环模型及演替模型。主要模拟植物种类在整个生态系统发展过程中的变化,以及植被类型的转变和相关的生物地球化学循环过程的改变,从而反映生物群落对气候变化的响应。3)景观生态系统,景观动态研究包含了时空两个方面的动态变化,一般可分为随机景观模型和基于过程的景观模型。随机模型用于模拟群落格局在演替过程中的动态变化等,基于过程的景观模型深入研究组成景观的各生态系统的空间结构。4)生物圈与地球生态系统,基于过程的陆地生物地球化学模式被用来研究自然生态系统中碳和其它矿物营养物质的潜在通量和蓄积量,较为流行的模式有陆地生态系统模式TEM、CENTURY、法兰克福生物圈模式FBM、Biome-BGC、卡内基-埃姆斯-斯坦福方法CASA等。这些模式己被用于估算自然生态系统对大气CO2加倍及相关气候变化在区域和全球尺度的平衡响应。最后,结合实际工作展望了生态系统模拟模型在各方面的发展方向。     

植被冠层尺度生理生态模型的研究进展

随着人们对植物生命活动各个过程研究的不断深入,以植物生理过程、物理过程为基础的各种生理生态学模型逐渐发展起来,而植被冠层尺度生理生态学过程模型已成为生态系统模型的核心之一。目前植被冠层尺度的大叶模型、多层模型、二叶模型以其成熟的理论基础及对植被冠层的光合作用、蒸腾作用较为成功的模拟,得到了广泛的应用。3个模型都以光合作用-气孔导度-蒸腾作用耦合模型为基础,但又具有各自的特点。本文对3种模型的结构及特点进行了总结,并对其进行了比较,简要介绍了目前植被冠层尺度生理生态学模型的应用及存在的问题和发展状况。     

光合作用-蒸腾作用-气孔导度的耦合模型及C_3植物叶片对环境因子的生理响应(英文)

以叶片的气体传输过程为基础,将蒸腾作用包括在以往光合作用气孔导度的耦合模型中,建立了光合作用蒸腾作用气孔导度的耦合模型。该模型可以模拟边界层导度对生理过程的影响。模拟了Ｃ３植物叶片对环境因子,如光照、温度、湿度、边界层导度和ＣＯ２浓度等的生理响应（光合作用、蒸腾作用、气孔导度）以及Ｃｉ和水分利用效率的变化。在环境因子变化于较大范围的情况下,模拟结果符合许多实验结论。     

Simulation of the Physiological Responses of C3 Plant Leaves to Environmental Factors by a Model Which Combines Stomatal Conductance,Photosynthesis and Transpiration

Transpiration element is included in the integrated stomatal conductance-photosynthesis model by considering gaseous transfer processes, so the present model is capable to simulate the influence of boundary layer conductance. Leuning in his revised Ball' s model replaced relative humidity with VPDs(the vapor pressure deficit from stomatal pore to leaf surface) and thereby made the relation with transpiration more straightforward, and made it possible for the regulation of transpiration and the influence of boundary layer conductance to be integrated into the combined model. If the differences in water vapor and CO2 concentration between leaf and ambient air are considered, VPDs, the evaporative demand, is influenced by stomatal and boundary layer conductance. The physiological responses of photosynthesis, transpiration, and stomatal function, and the changes of intercellular CO2 and water use efficiency to environmental factors, such as wind speed, photon flux density, leaf temperature and ambient CO2, are analyzed. It is shown that ff the boundary layer conductance drops to a level comparable with stomatal conductance, the results of simulation by the model presented here differ significantly from those by the previous model, and, in some cases, are more realistic than the latter.     

Strategies for measuring and modelling carbon dioxide and water vapour fluxes over terrestrial ecosystems

Continuous and direct measurements of ecosystem carbon dioxide and water vapour fluxes can improve our ability to close regional and global carbon and hydrological budgets. On this behalf, an international and multidisciplinary group of scientists (micrometeorologists, ecophysiologists and biogeochemists) assembled at La Thuile, Italy to convene a workshop on ‘Strategies for Monitoring and Modelling CO₂ and Water Vapour Fluxes over Terrestrial Ecosystems’. Over the course of the week talks and discussions focused on: (i) the results from recent field studies on the annual cycle of carbon dioxide and water vapour fluxes over terrestrial ecosystems; (ii) the problems and pitfalls associated with making long-term flux measurements; (iii) alternative methods for assessing ecosystem carbon dioxide and water vapour fluxes; (iv) how direct and continuous carbon dioxide and water vapour flux measurements could be used by the ecological and biogeochemical modelling communities; and (v) if, how and where to proceed with establishing a network of long-term flux measurement sites. This report discusses the purpose of the meeting and summarizes the conclusions drawn from the discussions by the attending scientists. There was a consensus that recent advances in instrumentation and software make possible long-term measurements of carbon dioxide and water vapour fluxes over terrestrial ecosystems. At this writing, eight research teams have conducted long-term carbon dioxide and water vapour flux experiments and more long-term studies are anticipated. The participants advocated an experimental design that would make long-term flux measurement valuable to a wider community of modelers, biogeochemists and ecologists. A network of carbon dioxide and water vapour flux measurement stations should include ancillary measurements of meteorological, ecological and biological variables. To assess spatial representativeness of the long term and tower-based flux measurements, periodic aircraft-based flux experiments and satellite-based assessments of land cover were recommended. Occasional cuvette-based measurements of leaf-level carbon dioxide and water vapour fluxes were endorsed to provide information on the biological control of surface fluxes. They can also provide data to parameterize ecophysiological models. Flask sampling of stable carbon isotopes was advocated to extend the flux measurements to the global scale.     

内蒙古克氏针茅草原生态系统-大气通量交换特征

基于内蒙古克氏针茅草原生态系统的涡动相关观测资料和小气候梯度系统观测资料,对研究区碳通量和水热通量的日、季动态进行了研究.结果表明：克氏针茅草原生态系统生长季的碳通量日动态呈U型曲线,即日出前释放CO₂,日出后开始吸收CO₂,正午前后达峰值,午后吸收CO₂减弱,日落后重新转为释放CO₂;9月白天CO₂吸收最为强烈,8月次之,10月最低.克氏针茅草原的感热和潜热通量的日动态均呈倒U型曲线,与碳通量日动态相反,即白天感热和潜热通量多为正值,夜间感热为负值,潜热接近于零;感热通量以5月最高,潜热通量以9月最高.冬季草地为弱碳源,CO₂通量较小,夏季表现为明显的碳汇.     

Significance of riverine carbon transport: A case study of a large tropical river, Godavari (India)

Although riverine carbon fluxes are a minor component of the global carbon cycle, the transfer of organic carbon from land to ocean represents a flux of potential carbon storage, irreversible over 103 to 104 a. Future carbon transfers through river basins are expected to accelerate, with respect to both sources and sinks, because of the large-scale human driven land-use and land-cover changes. Thus, the increased amounts of carbon transported to and sequestered in marine sediments (through fertilization by river-borne inorganic nutrients) may be an important net sink for anthropogenic CO2. Particularly, the humid tropics of South Asia are regions very sensitive to this lateral C transport because of high precipitation and high rates of land use and cover change. In this paper we report on the role of upland tributaries in the transport processes influencing the lateral carbon and nitrogen fluxes of the Godavari, a large tropical river of India. By far, dissolved inorganic carbon (DIC) is the dominant form of carbontransport in the river basin. It constitutes as much as 75% to the total carbonload. Particulate and dissolved organic carbon (POC and DOC) fluxes account for21% and 4%, respectively. In the upper basin, DOC fluxes exceed that of POC dueto large-scale anthropogenic activities. In contrast, tributaries in the central basin are characterized by comparable fluxes of POC and DOC. However, downriver POC export is 35% less than the import from upriver and tributaries due to theentrainment of sediments in river channels and dam sites. We argue that for highly disturbed watersheds in tropical regions, downstream transport of sediments and carbon requires long-term sampling programmes.     

Multiscale model intercomparisons of CO2 and H2O exchange rates in a maturing southeastern US pine forest

We compared four existing process‐based stand‐level models of varying complexity (physiological principles in predicting growth, photosynthesis and evapotranspiration, biogeochemical cycles, and stand to ecosystem carbon and evapotranspiration simulator) and a new nested model with 4 years of eddy‐covariance‐measured water vapor (LE) and CO₂ (Fc) fluxes at a maturing loblolly pine forest. The nested model resolves the ‘fast’ CO₂ and H₂O exchange processes using canopy turbulence theories and radiative transfer principles whereas slowly evolving processes were resolved using standard carbon allocation methods modified to improve leaf phenology. This model captured most of the intraannual variations in leaf area index (LAI), net ecosystem exchange (NEE), and LE for this stand in which maximum LAI was not at a steady state. The model comparisons suggest strong linkages between carbon production and LAI variability, especially at seasonal time scales. This linkage necessitates the use of multilayer models to reproduce the seasonal dynamics of LAI, NEE, and LE. However, our findings suggest that increasing model complexity, often justified for resolving faster processes, does not necessarily translate into improved predictive skills at all time scales. Additionally, none of the models tested here adequately captured drought effects on water and CO₂ fluxes. Furthermore, the good performance of some models in capturing flux variability on interannual time scales appears to stem from erroneous LAI dynamics and from sensitivity to droughts that injects unrealistic flux variability at longer time scales.     

基于CEVSA2模型的亚热带人工针叶林长期碳通量及碳储量模拟

随着造林活动的开展,准确评估人工林的碳储量和固碳能力,对于准确估算全球和区域碳平衡具有重要意义。基于生态系统机理模型为分析和预测人工林生态系统碳储量和碳汇功能的动态特征提供了重要手段。CEVSA2模型是在CEVSA模型的基础上,改进了碳水循环关键过程的定量表达方法而发展的新版本。基于改进后的CEVSA2模型,模拟分析了亚热带红壤丘陵区人工林自造林以来生态系统碳储量和碳通量的变化特征。模拟结果表明,造林后,植被碳持续增加,研究时段内平均每年的增长速率为22%。土壤碳储量在造林后最初的7-8a间是逐渐下降的,而后逐渐升高,约15a后土壤碳增加到初始水平,随后土壤碳继续增加。生态系统的总碳储量也表现为先降低后增加,造林4a后,总碳储量由降低转为增加趋势,6a后,总碳储量即超过造林当年的总碳储量。造林后,总初级生产力和净初级生产力逐渐升高,而总呼吸则先降低后升高,呼吸组分中自养呼吸所占比例逐渐升高而异养呼吸逐渐下降。人工林在造林初期表现为一个碳源,随着人工林的生长,碳汇功能逐渐增强。由此可见,造林初期,生态系统碳储量下降,生态系统向大气释放碳,随着人工林的生长,生态系统转变为一个碳汇,植被碳、土壤碳和总碳储量均显著增加。     

Comparing and evaluating process-based ecosystem model predictions of carbon and water fluxes in major European forest biomes

Process‐based models can be classified into: (a) terrestrial biogeochemical models (TBMs), which simulate fluxes of carbon, water and nitrogen coupled within terrestrial ecosystems, and (b) dynamic global vegetation models (DGVMs), which further couple these processes interactively with changes in slow ecosystem processes depending on resource competition, establishment, growth and mortality of different vegetation types. In this study, four models – RHESSys, GOTILWA+, LPJ‐GUESS and ORCHIDEE – representing both modelling approaches were compared and evaluated against benchmarks provided by eddy‐covariance measurements of carbon and water fluxes at 15 forest sites within the EUROFLUX project. Overall, model‐measurement agreement varied greatly among sites. Both modelling approaches have somewhat different strengths, but there was no model among those tested that universally performed well on the two variables evaluated. Small biases and errors suggest that ORCHIDEE and GOTILWA+ performed better in simulating carbon fluxes while LPJ‐GUESS and RHESSys did a better job in simulating water fluxes. In general, the models can be considered as useful tools for studies of climate change impacts on carbon and water cycling in forests. However, the various sources of variation among models simulations and between models simulations and observed data described in this study place some constraints on the results and to some extent reduce their reliability. For example, at most sites in the Mediterranean region all models generally performed poorly most likely because of problems in the representation of water stress effects on both carbon uptake by photosynthesis and carbon release by heterotrophic respiration (R_h). The use of flux data as a means of assessing key processes in models of this type is an important approach to improving model performance. Our results show that the models have value but that further model development is necessary with regard to the representation of the some of the key ecosystem processes.     

Simulated and observed fluxes of sensible and latent heat and CO2 at the WLEF-TV tower using SiB2.5

Three years of meteorological data collected at the WLEF‐TV tower were used to drive a revised version of the Simple Biosphere (SiB 2.5) Model. Physiological properties and vegetation phenology were specified from satellite imagery. Simulated fluxes of heat, moisture, and carbon were compared to eddy covariance measurements taken onsite as a means of evaluating model performance on diurnal, synoptic, seasonal, and interannual time scales. The model was very successful in simulating variations of latent heat flux when compared to observations, slightly less so in the simulation of sensible heat flux. The model overestimated peak values of sensible heat flux on both monthly and diurnal scales. There was evidence that the differences between observed and simulated fluxes might be linked to wetlands near the WLEF tower, which were not present in the SiB simulation. The model overestimated the magnitude of the net ecosystem exchange of CO₂ in both summer and winter. Mid‐day maximum assimilation was well represented by the model, but late afternoon simulations showed excessive carbon uptake due to misrepresentation of within‐canopy shading in the model. Interannual variability was not well simulated because only a single year of satellite imagery was used to parameterize the model.