基于数据同化的哈佛森林地区水、碳通量模拟

模型模拟和站点观测是陆地生态系统水、碳循环研究最主要的两种手段,但各有优势和不足,若二者相互结合,则能更准确地反映生态系统水、碳通量的动态变化.数据同化为模型与观测结合提供了一条有效的途径.本文采用哈佛森林环境监测站相关数据,利用集合卡曼滤波同化算法,将实测叶面积指数(LAI)和遥感LAI同化进入Biome BGC模型中,对该地区水、碳通量进行模拟.结果表明：与未同化模拟相比,将1998、1999和2006年实测LAI数据同化后,模型模拟碳通量(NEE)与通量观测NEE的决定系数(R²)平均提升8.4%;蒸散发(ET)的R²平均提升10.6%;NEE的绝对误差和(SAE)和均方根误差(RMSE)平均下降17.7%和21.2%,ET的SAE和RMSE平均下降26.8%和28.3%.将2000-2004年MODIS LAI 产品与模型同化后,NEE、ET模拟值与观测值间的R²分别提升7.8%和4.7%;NEE的SAE和 RMSE分别下降21.9%和26.3%,ET的SAE和 RMSE分别下降24.5%和25.5%.无论实测LAI还是遥感观测LAI,同化进入模型都能不同程度地提高水碳通量的模拟精度.     

改进Biome-BGC模型模拟哈佛森林地区水、碳通量

Biome-BGC模型通过耦合植被、土壤与大气间的水分与CO2交换过程,实现植被生产力的模拟,但土壤水平衡模块的不够完善,导致在长时间无降水情况下植被生产力模拟存在较大误差.针对这一问题,本文对Biome-BGC模型中土壤水分胁迫气孔导度方程、蒸散计算公式及土壤水分流失过程等3方面进行了改进和调整,利用改进的Biome-BGC模型模拟美国哈佛森林地区蒸散、植被生产力,并与地面通量观测值进行了比较.结果表明,改进后模拟精度有明显的提高,蒸散、植被生态系统生产力(NEE)与观测值间的决定系数分别由0.483和0.658提高到0.617和O.813,蒸散逐年均方根误差平均下降了48.7％,NEE逐年误差平方和平均下降了39.8％.改进后的模型模拟结果更接近观测值.     

基于植被羰基硫通量估算陆地生态系统总初级生产力研究进展

羰基硫(COS)是大气中的长周期痕量气体,其分子结构、对流层大气混合比的昼夜和季节动态类似于二氧化碳(CO₂)。植物光合作用及其水解过程中,受扩散通路导度和酶活性影响,气孔的COS与CO₂吸收紧密相关,同时,植物自养呼吸并不释放COS。最新研究中,采用植被COS通量直接指示生态系统总初级生产力(GPP)。综述了植被COS通量与光合作用中碳固定过程的关联机制,以及采用涡度相关观测、整合大气COS监测和生态系统过程模型等方法开展植被COS通量与GPP研究的最新进展,探讨了关键生态过程和参数,发现方法存在以下瓶颈：(1)生理过程、尺度效应和解析效应影响了COS与CO₂的叶片相对吸收率,(2)观测与模拟手段有待进一步耦合,(3)全球COS观测密度限制了方法验证,(4)硫循环过程影响了多区域模拟精度。方法发展的前沿领域包括：(1)开展重点地区植被COS通量观测,(2)提高COS卫星柱浓度的覆盖范围,(3)完善生态系统过程模型的COS吸收机理。展望未来研究关注的科学问题是：对于亚热带等尚待开展COS连续观测的区域,采用植被COS通量...     

陆地植被暗呼吸的研究进展

全球变化背景下陆地植物的源汇效应一直是陆地生态系统研究的热点之一.暗呼吸在碳循环中占有重要的位置,是全球变化背景下碳循环过程研究的一个重要环节.目前国内外有关植物暗呼吸方面的研究还较少.本文就植物暗呼吸作用的生理过程、暗呼吸的观测方法,以及植物自身生物因素和环境因子对暗呼吸的影响进行了介绍,指出植物暗呼吸研究中存在的不确定性,并对后续研究的热点与方向进行了展望.     

祁连山不同植被类型土壤碳贮量和碳通量

采用野外调查测定、野外定位观测和室内分析相结合的方法,在植被类型变化较大林区,选择邻近相同海拔、坡向和土壤类型的天然林(青海云杉林、祁连圆柏林、高山灌丛林)、人工林(13年生华北落叶松林)、牧坡草地和农田等植被类型土壤为研究对象,研究了祁连山不同植被类型的土壤碳动态.结果表明:天然林、牧坡草地、农田和人工林的土壤有机碳含量分别为59.45～84.7、78.30、13.51和43.25 g·kg-1,平均土壤有机碳密度分别为15.96～19.95、17.74、10.63和15.97 kg·m-2,土壤有机碳平均周转时间分别为27～36、25、23和33 a;不同植被类型土壤CO2通量依次为青海云杉林584.03 g C·m-2·a-1,祁连圆柏林517.63 g C·m-1·a-1,高山灌丛林601.00 g C·m-2·a-1,牧坡草地796.89 g C·m-2·a-1,农田281.75 g C·m-1·a-1,人工林569.92 g C·m-2·a-1;同一植被类型中,土壤有机碳含量和土壤碳密度随土壤深度增加而降低,而土壤有机碳周转时间则随深度增加而增大.     

陆地生态系统植被氮磷化学计量研究进展

因化学功能的耦合和元素的不可替代性, 植物对N、P的需求和利用存在严格的比例。植物N、P化学计量在不同功能群、生长地区、生长季、器官之间以及环境梯度下存在明显的变化规律。多数研究从N、P浓度、N:P及N、P间异速指数等角度分析了植物化学计量变化规律, 并探讨其在全球范围内的具体数值。为增进对植物响应全球变化的理解, 该文综述了N、P化学计量的影响因素及其机理的最新研究进展, 并指出未来拟重点研究的方向。     

陆地植被的固碳功能与适用于碳贸易的生物固碳方式

碳贸易的核心问题是要有足够的碳封存量在抵消CO₂的排放之后还能有碳额度进入市场买卖。该文结合固碳概念,从固碳技术、减量成本、对生态系统碳汇功能的影响等多方面对目前存在的和有潜力的各种减排与固碳途径进行了比较分析,认为陆地植被对CO₂的吸收是最安全有效的固碳过程,它们能够在一定的浓度范围内吸收CO₂,从而节省分离、提纯等技术的费用。进而该文分别对森林、草地、农田等3种陆地植被的固碳功能与不同固碳策略对固碳效果的影响两个方面进行详细具体的比较分析,得出森林生态系统具有强大的碳吸收能力,草地与农田土壤有机碳库在固碳方面的作用也十分显著。最后结合我国实际,提出4项适用于碳贸易的生物固碳方式,即保护天然林,推广种植速生丰产人工林;保育天然草地、建设人工草地;建立规模化沼气产业链;注重利用边际土地种植生物质能源,促进生物质能源的开发。     

基于通量塔净生态系统碳交换数据的植被物候遥感识别方法评价

选择北美洲72座通量塔观测的净生态系统碳交换（NEE）数据来计算植被物候,并以此作为参考数据,从可行性和准确性两方面对阈值法、移动平均法和函数拟合法三大类常用的植被物候遥感识别方法进行了综合评价.结果表明： 基于局部中值的阈值法对植被物候识别的可行性和准确性均最优;其次为Logistic函数拟合法中的一阶导数方法;移动平均法对植被物候识别的可行性和准确性与移动窗口的大小有关,对于16 d合成的归一化差值植被指数（NDVI）时间序列数据来说,移动窗口大小为15时能获得较优的结果;而全局阈值法对植被物候识别的可行性和准确性均最差;Logistic函数拟合法中的曲率变化率方法在识别植被物候时虽然与基于NEE数据得到的植被物候在数值上存在较大偏差,但二者之间具有较高的相关性,说明基于曲率变化率方法识别出的植被物候能较真实地反映植被物候在时空上的变化趋势.     

基于通量塔净生态系统碳交换数据的植被物候遥感识别方法评价

选择北美洲72座通量塔观测的净生态系统碳交换（NEE）数据来计算植被物候,并以此作为参考数据,从可行性和准确性两方面对阈值法、移动平均法和函数拟合法三大类常用的植被物候遥感识别方法进行了综合评价.结果表明： 基于局部中值的阈值法对植被物候识别的可行性和准确性均最优;其次为Logistic函数拟合法中的一阶导数方法;移动平均法对植被物候识别的可行性和准确性与移动窗口的大小有关,对于16 d合成的归一化差值植被指数（NDVI）时间序列数据来说,移动窗口大小为15时能获得较优的结果;而全局阈值法对植被物候识别的可行性和准确性均最差;Logistic函数拟合法中的曲率变化率方法在识别植被物候时虽然与基于NEE数据得到的植被物候在数值上存在较大偏差,但二者之间具有较高的相关性,说明基于曲率变化率方法识别出的植被物候能较真实地反映植被物候在时空上的变化趋势.     

中国陆地生态系统土壤有机碳变化研究进展

通过文献资料, 对中国陆地生态系统土壤有机碳变化研究进行评述. 20世纪80年代初至21世纪初, 中国森林、草地、灌丛和农田土壤有机碳库合计年均增加(71±19) Tg/a, 三江平原沼泽湿地垦殖导致土壤有机碳损失(6±2) Tg/a. 该结果存在极大的不确定性, 尤其是对森林、灌丛和草地碳库变化的估计. 未来研究需重点关注土地利用变化及其碳源、碳汇效应, 放牧管理对草地土壤有机碳库的影响, 灌丛和非森林树木(经济林、防护林及四旁绿化造林)土壤有机碳变化估算, 深层土壤有机碳变化的测定和估算, 中国土壤的固碳潜力及陆地生态系统碳收支模型开发.     

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。     

喀斯特城市地表水热通量的时空变化研究

针对我国西南地区桂林喀斯特城市近20多年来快速扩展所引发的热环境问题,改进METRIC模型使其适用于喀斯特城市实际状况,利用模型和1994—2015年5景Landsat遥感图像反演地表水热通量,分析通量时空变化规律。结果表明,潜热通量从高到低依次为水体、喀斯特山峰阳坡植被、地面植被、喀斯特山峰阴坡植被、建筑/道路和裸土、喀斯特山峰裸岩,显热通量从高到低依次为喀斯特山峰裸岩和建筑/道路、裸土、喀斯特山峰阳坡植被、地面植被、喀斯特山峰阴坡植被、水体。水热通量随时间的变化受地表覆盖变化的影响,研究区波文比(显热通量与潜热通量比值)在1994年最高,达到1.62,2000年下降到1.24,之后逐渐升高至2015年的1.51。城市扩展过程出现的显热高值区和潜热低值区比例低于10%,其变化引发显热中低值区和潜热中高值区比例的变化,显热高值区最高比例在1994年(10.0%),2000年下降到5.4%,之后至2010年逐渐上升到9.4%,但2015年下降到7.1%,潜热低值区比例的变化趋势与显热高值区比例基本相同。植被覆盖度(Vegetation fraction,Pv)在0.1—0.8范围时对水热...     

A coupled carbon and water flux model to predict vegetation structure

Abstract. A coupled carbon and water flux model (BIOME2) captures the broad-scale environmental controls on the natural distribution of vegetation structural and phenological types in Australia. Model input consists of latitude, soil type, and mean monthly climate (temperature, precipitation, and sunshine hours) data on a 1/10° grid. Model output consists of foliage projective cover (FPC) for the quantitative combination of plant types that maximizes net primary production (NPP). The model realistically simulates changes in FPC along moisture gradients as a consequence of the trade-off between light capture and water stress. A two-layer soil hydrology model also allows simulation of the competitive balance between grass and woody vegetation including the strong effects of soil texture.     

Oxygen and carbon dioxide fluxes from barley shoots depend on nitrate assimilation

A custom oxygen analyzer in conjunction with an infrared carbon dioxide analyzer and humidity sensors permitted simultaneous measurements of oxygen, carbon dioxide, and water vapor fluxes from the shoots of intact barley plants (Hordeum vulgare L. cv Steptoe). The oxygen analyzer is based on a calciazirconium sensor and can resolve concentration differences to within 2 microliters per liter against the normal background of 210,000 microliters per liter. In wild-type plants receiving ammonium as their sole nitrogen source or in nitrate reductase-deficient mutants, photosynthetic and respiratory fluxes of oxygen equaled those of carbon dioxide. By contrast, wild-type plants exposed to nitrate had unequal oxygen and carbon dioxide fluxes: oxygen evolution at high light exceeded carbon dioxide consumption by 26% and carbon dioxide evolution in the dark exceeded oxygen consumption by 25%. These results indicate that a substantial portion of photosynthetic electron transport or respiration generates reductant for nitrate assimilation rather than for carbon fixation or mitochondrial electron transport.     

A model of carbon dioxide assimilation in Chlamydomonas reinhardii

A simple model of photosynthetic CO₂ assimilation in Chlamydomonas has been developed in order to evaluate whether a CO₂-concentrating system could explain the photosynthetic characteristics of this alga (high apparent affinity for CO₂, low photorespiration, little O₂ inhibition of photosynthesis, and low CO₂ compensation concentration). Similarly, the model was developed to evaluate whether the proposed defects in the CO₂-concentrating system of two Chlamydomonas mutants were consistent with their observed photosynthetic characteristics. The model treats a Chlamydomonas cell as a single compartment with two carbon inputs: passive diffusion of CO₂, and active transport of HCO ₃ ^- . Internal inorganic carbon was considered to have two potential fates: assimilation to fixed carbon via ribulose 1,5-bisphosphate carboxylase-oxygenase or exiting the cell by either passive CO₂ diffusion or reversal of HCO ₃ ^- transport. Published values for kinetic parameters were used where possible. The model accurately reproduced the CO₂-response curves of photosynthesis for wild-type Chlamydomonas, the two mutants defective in the CO₂-concentrating system, and a double mutant constructed by crossing these two mutants. The model also predicts steady-state internal inorganic-carbon concentrations in reasonable agreement with measured values in all four cases. Carbon dioxide compensation concentrations for wild-type Chlamydomonas were accurately predicted by the model and those predicted for the mutants were in qualitative agreement with measured values. The model also allowed calculation of approximate energy costs of the CO₂-concentrating system. These calculations indicate that the system may be no more energy-costly than C₄ photosynthesis.Abbreviations Chl chlorophyll - RuBPC/O ribulose 1,5-bisphosphate carboxylase-oxygenase - CA carbonic anhydrase     

Seasonal carbon dynamics and water fluxes in an Amazon rainforest

Satellite‐based observations indicate that seasonal patterns in canopy greenness and productivity in the Amazon are negatively correlated with precipitation, with increased greenness occurring during the dry months. Flux tower measurements indicate that the canopy greening that occurs during the dry season is associated with increases in net ecosystem productivity (NEP) and evapotranspiration (ET). Land surface and terrestrial biosphere model simulations for the region have predicted the opposite of these observed patterns, with significant declines in greenness, NEP, and ET during the dry season. In this study, we address this issue mainly by developing an empirically constrained, light‐controlled phenology submodel within the Ecosystem Demography model version 2 (ED2). The constrained ED2 model with a suite of field observations shows markedly improved predictions of seasonal ecosystem dynamics, more accurately capturing the observed patterns of seasonality in water, carbon, and litter fluxes seen at the Tapajos National Forest, Brazil (2.86°S, 54.96°W). Long‐term simulations indicate that this light‐controlled phenology increases the resilience of Amazon forest NEP to interannual variability in climate forcing.     

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.     

陆地水-碳耦合模拟研究进展

在全球气候变化和水资源危机背景下,人类对土地、森林和水资源的适应性管理需求推动了生态系统水、碳耦合与制约关系的研究.在多时空尺度上研究水、碳耦合关系、以及探讨全球变化下生态系统水、碳平衡及其相互响应机制是现阶段的研究热点.本文在综述不同尺度水、碳耦合关系的基础上,探讨了其中关键过程与参数的涵义和测算方法,分析了大尺度上基于遥感技术的蒸散发模型的构建及其对水碳耦合研究的重要性,最后展望了多源数据同化技术等在未来气候变化背景下水碳耦合模拟中的应用.