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1.
生态系统模型是模拟全球陆地生态系统碳循环的重要工具,但是其在全球不同区域的模拟存在很大的不确定性。如何评估陆地生态系统模型的不确定性是一项重要的研究。以北美地区为例,利用8个高塔观测站点同步获取的大气CO2和羰基硫(OCS)浓度数据,结合WRF-STILT大气粒子扩散模型,评估了CASA-GFED3、SiB3和SiBCASA三种陆地生态系统模型模拟总初级生产力(GPP)和净生态系统CO2交换(NEE)通量的不确定性。结果表明,SiB3模型能很好地模拟北美陆地生态系统GPP和NEE的季节变化时相和幅度,在3种模型中具有最佳的模拟能力;CASA-GFED3模型模拟的NEE季节变化较为理想、但对生长季GPP的模拟存在较大的误差,SiBCASA模型在模拟冬季晚期和春季早期的NEE和GPP时表现较不理想。研究证明了大气CO2和OCS在评估陆地生态系统模型碳通量模拟的不确定性中的作用,为利用大气CO2和OCS观测数据优化计算陆地生态系统光合和呼吸碳通量提供了理论支撑。 相似文献
2.
羰基硫(COS)和CO2化学结构相似,且植物对COS和CO2具有共吸收特性,因此可利用COS作为示踪物来估算生态系统总初级生产力,而不同植物吸收COS和CO2对环境因子变化的响应差异较大。以南亚热带典型树种马尾松(Pinus massoniana)和杉木(Cunninghamia lanceolata)为研究对象,设置2个氮水平及3个土壤水分梯度处理。采取顶空套袋法采集气体样品,用预浓缩—气质联用仪分析样品COS浓度,同时测量植物光合参数。结果表明:马尾松和杉木吸收COS,吸收速率均值分别为39.58—127.27 pmol m-2 s-1和0.81—66.92 pmol m-2 s-1。整体而言,施氮可促进植物吸收COS,但除施氮对马尾松COS通量有显著影响外(P<0.05),施氮、土壤水分和两者交互作用对马尾松和杉木的COS和CO2通量及其比值均无显著性影响。施氮情况下,高土壤水分处理促进马尾松COS吸... 相似文献
3.
二氧化碳储存通量对森林生态系统碳收支的影响 总被引:5,自引:0,他引:5
涡度相关系统观测高度以下的CO2储存通量对准确评价森林生态系统与大气间净CO2交换量(NEE)有着重要的影响.本研究以长白山阔叶红松林为研究对象,利用2003年的涡度相关观测数据以及CO2浓度廓线数据,分析了CO2储存通量的变化规律及其对碳收支过程的影响.结果表明:涡度相关观测高度以下的CO2储存通量具有典型的日变化特征,其最大变化量出现在大气稳定与不稳定层结转换期.利用涡度相关系统观测的单点CO2浓度变化方法与利用CO2浓度廓线方法计算的CO2储存通量差异不显著.忽略CO2储存通量,在半小时尺度上会造成对夜间和白天的NEE分别低估25%和19%,在日和年尺度上,会对NEE低估10%和25%;忽略CO2储存通量,会低估Michaelis-Menten光响应方程及Lloyd-Taylor呼吸方程的参数,并且对表观初始量子效率α和参考呼吸Rref的低估最大;忽略CO2储存通量,在半小时、日及年尺度上,均会对总光合作用(GPP)和生态系统呼吸(Re)低估约20%. 相似文献
4.
首先介绍静态暗箱法气相色谱法观测确定陆地生态系统地气CO2净交换通量的基本原理和方法,然后讨论在开放式空气CO2增加(FACE)试验中应用该原理和方法观测研究大气CO2浓度升高对稻田生态系统大气CO2净交换通量的影响.因缺乏必要参数的实际观测值,本文只能根据暗箱观测值计算CO2净交换通量的最小取值NEEmin.NEEmin计算结果表明,在插秧1个月之后的水稻生长期内,大气CO2浓度升高200±40μmol·mol-1使稻田生态系统对大气CO2的净吸收约为对照的3倍.为根据暗箱观测准确确定NEE,还必须在FACE和对照条件下观测水稻植株的暗维持呼吸系数、地上生物量及根冠比动态. 相似文献
5.
生态系统总初级生产力(GPP)是全球生态系统碳循环研究的重要组成部分.植被最大光能利用率(εmax)是陆地生态系统GPP模拟的关键参数.本文基于植被光合模型(VPM)和全球通量网(FLUXNET)40个站点(179条站点年数据)的涡度相关通量观测数据,采用单因素轮换法对VPM模型进行参数敏感性分析,并利用交叉验证法对全球森林生态系统的光合作用关键参数进行优化和验证.结果表明:森林生态系统GPP模型受εmax、光合最高温度(Tmax)以及光合最适温度(Topt)的影响最大;优化后的εmax在不同植被类型之间存在明显差异,介于0.05~0.08 μmol CO2·μmol-1 PAR,常绿阔叶林>常绿针叶林>混交林>落叶阔叶林;优化后的森林生态系统Tmax为38~48 ℃,Topt为18~22 ℃;利用分植被类型优化后的模型关键参数,VPM模型可较好地模拟全球主要森林生态系统GPP的季节和年际变化. 相似文献
6.
湿地生态系统是吸收全球大气二氧化碳(CO2)的汇,同时土壤厌氧环境造成其是大气甲烷(CH4)的源。尽管有证据表明,湿地生态系统CH4排放部分抵消其对大气CO2的净吸收,但目前未见全球尺度湿地CH4排放对其净生态系统CO2交换(NEE)抵消效应的研究。本研究分析了全球内陆湿地(泥炭湿地和非泥炭湿地)以及滨海湿地(海草床、盐沼和红树林)中同时测定湿地NEE和CH4排放通量的数据。结果表明:各类型湿地生态系统均为大气CO2的汇,NEE值排序为红树林(-2011.0 g CO2·m-2·a-1)<盐沼(-1636.6 g CO2·m-2·a-1)<非泥炭地(-870.8 g CO2·m-2·a-1)<泥炭地(... 相似文献
7.
青藏高原草甸草原是生态系统中重要的植被类型,准确评估高寒草甸草原生态系统碳源汇状况及碳储量变化尤为重要。基于涡度相关系统观测,分析了2009年至2016年8年期间青海湖北岸草甸草原环境因子以及碳通量的变化特征,运用结构方程模型(SEM)分析环境因子对总初级生产力(GPP)、净生态系统CO2交换量(NEE)、生态系统呼吸(Re)的调控机制。结果表明:2009—2016年8年NEE日均值在-2.02—0.88 gC m-2 d-1之间,5—9月NEE为负值,表现为碳吸收,雨热同期的6、7、8月是CO2净吸收最强的时期,平均每月吸收CO2 39.85 gC m-2 month-1,NEE负值日数约占全年的48%,10月—翌年4月为正值,表现为碳释放,初春3月和秋末11月是CO2净释放最强的时期;Re日均值为1.69 gC m-2 d-1,受季节温度的影响,呈夏季强,冬季弱的态... 相似文献
8.
大气CO2浓度升高影响植物光合作用过程和生物量积累,改变植物地上和地下生物量的动态分配.土壤有机质的形成和周转依赖于植物组分的输入,因此,CO2浓度升高所造成的植物生理和代谢的变化对土壤碳库收支平衡具有重要影响.采用稳定碳同位素(13C)技术研究土壤-植物系统的碳循环可阐明大气CO2浓度升高条件下光合碳在植物各器官的分配特征和时间动态,明确光合碳在土壤中的积累、分解与迁移转化过程以及对土壤有机碳库周转的影响.本文综述了基于13C自然丰度法或13C示踪技术研究大气CO2浓度升高对土壤-植物系统碳循环的影响,主要包括:1)对植物光合作用的同位素分馏的影响;2)对植物光合碳(新碳)分配动态的影响;3)对土壤有机碳新老碳库动态以及微生物转化过程的影响.明确上述过程及其调控机制可为预测CO2浓度升高对陆地生态系统碳循环及源汇效应的长期影响奠定基础. 相似文献
9.
生态系统光合和呼吸是构成净生态系统CO2交换量(NEE)的重要组分。涡度相关技术可直接观测生态系统NEE,并通过建立温度回归或光响应曲线等函数将NEE统计拆分为生态系统光合和呼吸,但是存在自相关和高估白天呼吸等问题。稳定同位素红外光谱技术的进步使高时间分辨率大气CO2及其稳定碳同位素组成(δ13C)的连续观测成为可能,与涡度相关技术观测的NEE数据相结合,可实现昼夜和季节尺度生态系统光合和呼吸拆分。本文系统阐述了生态系统光合与呼吸的同位素通量拆分方法的基本理论与假设,阐述了同位素通量观测技术的发展及其应用进展,综述了同位素通量拆分理论解析生态系统光合与呼吸过程的新机制认识,最后总结并展望了同位素通量拆分理论的不确定性以及开展多种拆分方法综合比较的必要性。 相似文献
10.
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. 相似文献
11.
S. LUYSSAERT † I. A. JANSSENS M. SULKAVA‡ D. PAPALE§ A. J. DOLMAN¶ M. REICHSTEIN J. HOLLMÉN‡ J. G. MARTIN† T. SUNI T. VESALA D. LOUSTAU†† B. E. LAW† E. J. MOORS‡‡ 《Global Change Biology》2007,13(10):2110-2127
The growth rate of atmospheric CO2 exhibits large temporal variation that is largely determined by year‐to‐year fluctuations in land–atmosphere CO2 fluxes. This land–atmosphere CO2‐flux is driven by large‐scale biomass burning and variation in net ecosystem exchange (NEE). Between‐ and within years, NEE varies due to fluctuations in climate. Studies on climatic influences on inter‐ and intra‐annual variability in gross photosynthesis (GPP) and net carbon uptake in terrestrial ecosystems have shown conflicting results. These conflicts are in part related to differences in methodology and in part to the limited duration of some studies. Here, we introduce an observation‐driven methodology that provides insight into the dependence of anomalies in CO2 fluxes on climatic conditions. The methodology was applied on fluxes from a boreal and two temperate pine forests. Annual anomalies in NEE were dominated by anomalies in GPP, which in turn were correlated with incident radiation and vapor pressure deficit (VPD). At all three sites positive anomalies in NEE (a reduced uptake or a stronger source than the daily sites specific long‐term average) were observed on summer days characterized by low incident radiation, low VPD and high precipitation. Negative anomalies in NEE occurred mainly on summer days characterized by blue skies and mild temperatures. Our study clearly highlighted the need to use weather patterns rather than single climatic variables to understand anomalous CO2 fluxes. Temperature generally showed little direct effect on anomalies in NEE but became important when the mean daily air temperature exceeded 23 °C. On such days GPP decreased likely because VPD exceeded 2.0 kPa, inhibiting photosynthetic uptake. However, while GPP decreased, the high temperature stimulated respiration, resulting in positive anomalies in NEE. Climatic extremes in summer were more frequent and severe in the South than in the North, and had larger effects in the South because the criteria to inhibit photosynthesis are more often met. 相似文献
12.
Gianluca Tramontana Mirco Migliavacca Martin Jung Markus Reichstein Trevor F. Keenan Gustau Camps‐Valls Jerome Ogee Jochem Verrelst Dario Papale 《Global Change Biology》2020,26(9):5235-5253
The eddy covariance (EC) technique is used to measure the net ecosystem exchange (NEE) of CO2 between ecosystems and the atmosphere, offering a unique opportunity to study ecosystem responses to climate change. NEE is the difference between the total CO2 release due to all respiration processes (RECO), and the gross carbon uptake by photosynthesis (GPP). These two gross CO2 fluxes are derived from EC measurements by applying partitioning methods that rely on physiologically based functional relationships with a limited number of environmental drivers. However, the partitioning methods applied in the global FLUXNET network of EC observations do not account for the multiple co‐acting factors that modulate GPP and RECO flux dynamics. To overcome this limitation, we developed a hybrid data‐driven approach based on combined neural networks (NNC‐part). NNC‐part incorporates process knowledge by introducing a photosynthetic response based on the light‐use efficiency (LUE) concept, and uses a comprehensive dataset of soil and micrometeorological variables as fluxes drivers. We applied the method to 36 sites from the FLUXNET2015 dataset and found a high consistency in the results with those derived from other standard partitioning methods for both GPP (R2 > .94) and RECO (R2 > .8). High consistency was also found for (a) the diurnal and seasonal patterns of fluxes and (b) the ecosystem functional responses. NNC‐part performed more realistic than the traditional methods for predicting additional patterns of gross CO2 fluxes, such as: (a) the GPP response to VPD, (b) direct effects of air temperature on GPP dynamics, (c) hysteresis in the diel cycle of gross CO2 fluxes, (d) the sensitivity of LUE to the diffuse to direct radiation ratio, and (e) the post rain respiration pulse after a long dry period. In conclusion, NNC‐part is a valid data‐driven approach to provide GPP and RECO estimates and complementary to the existing partitioning methods. 相似文献
13.
Terrestrial higher-plant response to increasing atmospheric [CO2 ] in relation to the global carbon cycle 总被引:5,自引:0,他引:5
JEFFREY S. AMTHOR 《Global Change Biology》1995,1(4):243-274
Terrestrial higher plants exchange large amounts of CO2 with the atmosphere each year; c. 15% of the atmospheric pool of C is assimilated in terrestrial-plant photosynthesis each year, with an about equal amount returned to the atmosphere as CO2 in plant respiration and the decomposition of soil organic matter and plant litter. Any global change in plant C metabolism can potentially affect atmospheric CO2 content during the course of years to decades. In particular, plant responses to the presently increasing atmospheric CO2 concentration might influence the rate of atmospheric CO2 increase through various biotic feedbacks. Climatic changes caused by increasing atmospheric CO2 concentration may modulate plant and ecosystem responses to CO2 concentration. Climatic changes and increases in pollution associated with increasing atmospheric CO2 concentration may be as significant to plant and ecosystem C balance as CO2 concentration itself. Moreover, human activities such as deforestation and livestock grazing can have impacts on the C balance and structure of individual terrestrial ecosystems that far outweigh effects of increasing CO2 concentration and climatic change. In short-term experiments, which in this case means on the order of 10 years or less, elevated atmospheric CO2 concentration affects terrestrial higher plants in several ways. Elevated CO2 can stimulate photosynthesis, but plants may acclimate and (or) adapt to a change in atmospheric CO2 concentration. Acclimation and adaptation of photosynthesis to increasing CO2 concentration is unlikely to be complete, however. Plant water use efficiency is positively related to CO2 concentration, implying the potential for more plant growth per unit of precipitation or soil moisture with increasing atmospheric CO2 concentration. Plant respiration may be inhibited by elevated CO2 concentration, and although a naive C balance perspective would count this as a benefit to a plant, because respiration is essential for plant growth and health, an inhibition of respiration can be detrimental. The net effect on terrestrial plants of elevated atmospheric CO2 concentration is generally an increase in growth and C accumulation in phytomass. Published estimations, and speculations about, the magnitude of global terrestrial-plant growth responses to increasing atmospheric CO2 concentration range from negligible to fantastic. Well-reasoned analyses point to moderate global plant responses to CO2 concentration. Transfer of C from plants to soils is likely to increase with elevated CO2 concentrations because of greater plant growth, but quantitative effects of those increased inputs to soils on soil C pool sizes are unknown. Whether increases in leaf-level photosynthesis and short-term plant growth stimulations caused by elevated atmospheric CO2 concentration will have, by themselves, significant long-term (tens to hundreds of years) effects on ecosystem C storage and atmospheric CO2 concentration is a matter for speculation, not firm conclusion. Long-term field studies of plant responses to elevated atmospheric CO2 are needed. These will be expensive, difficult, and by definition, results will not be forthcoming for at least decades. Analyses of plants and ecosystems surrounding natural geological CO2 degassing vents may provide the best surrogates for long-term controlled experiments, and therefore the most relevant information pertaining to long-term terrestrial-plant responses to elevated CO2 concentration, but pollutants associated with the vents are a concern in some cases, and quantitative knowledge of the history of atmospheric CO2 concentrations near vents is limited. On the whole, terrestrial higher-plant responses to increasing atmospheric CO2 concentration probably act as negative feedbacks on atmospheric CO2 concentration increases, but they cannot by themselves stop the fossil-fuel-oxidation-driven increase in atmospheric CO2 concentration. And, in the very long-term, atmospheric CO2 concentration is controlled by atmosphere-ocean C equilibrium rather than by terrestrial plant and ecosystem responses to atmospheric CO2 concentration. 相似文献
14.
中国陆地生态系统通量观测站点空间代表性 总被引:1,自引:3,他引:1
涡度相关技术是测定大气与陆地生态系统之间CO2交换、水分和能量通量最直接的方法,可用于研究土壤、植被与大气间的CO2交换及其调控机制。收集了11个影响净碳交换量的主要变量信息,包括气象因素、土壤因素和地形因素的非生物因子、实际植被状态以及植被生产力,采用多元地理变量空间聚类分析方法,绘制出不同聚类数(25、50、75、85、100、150和200类)的通量生态区。结合中国现有通量观测站点的空间分布格局,与新生成的通量生态区和已有的自然地理区划进行对比分析,发现由于中国地形复杂,生态系统类型多样,现有85个涡度相关通量观测站点仅能刻画部分中国生态系统类型的净碳交换量时空特征,通量生态区划分为100-150类比较合适。考虑到涡度相关通量观测运行成本,通量站点可增加至150个,从而使得优化后的通量观测网络能够代表中国主要类型的生态系统,并且有利于通量观测数据与遥感资料的有效结合,提高碳水通量观测从站点扩展到区域尺度的精度,从而更好地检验过程机理模型的模拟结果。 相似文献
15.
A simple calibrated model of Amazon rainforest productivity based on leaf biochemical properties 总被引:9,自引:4,他引:5
J. LLOYD J. GRACE A. C. MIRANDA P. MEIR S. C. WONG H. S. MIRANDA I. R. WRIGHT J. H. C. GASH J. McINTYRE 《Plant, cell & environment》1995,18(10):1129-1145
A simple ‘big leaf’ ecosystem gas exchange model was developed, using eddy covariance data collected at an undisturbed tropical rainforest in south-western Amazonia (Brazil). The model used mechanistic equations of canopy biochemistry combined with an empirical stomatal model describing responses to light, temperature and humidity. After calibration, the model was driven using hourly data from a weather station at the top of the tower at the measurement site, yielding an estimate of gross primary productivity (annual photosynthesis) in 1992/1993 of about 200 mol C m?2 year ?. Although incoming photon flux density emerged as the major control on photosynthesis in this forest, at a given PAR CO2 assimilation rates were higher in the mornings than in the afternoons. This was attributable to stomatal closure in the afternoon in response to increasing canopy-to-air vapour pressure differences. Although most morning gas exchange was clearly limited by the rate of electron transport, afternoon gas exchange was generally observed to be very nearly co-limited by both Rubisco activity (Vmax) and electron transport rate. The sensitivity of the model to changes in nitrogen allocation showed that the modelled ratio of Vmax to electron transport (Jmax) served nearly to maximize the annual carbon gain, and indeed, would have resulted in almost maximum annual carbon gain at the pre-industrial revolution atmospheric CO2 concentration of 27 Pa. Modelled gross primary productivity (GPP) was somewhat lower at 27 Pa, being about 160 mol C m?2 year?1. The model suggests that, in the absence of any negative feedbacks on GPP, future higher concentrations of atmospheric CO2 will continue to increase the GPP of this rainforest, up to about 230 mol C m?2 year?1 at 70 Pa. 相似文献
16.
Fulin Yang Rafat Qubaja Fyodor Tatarinov Eyal Rotenberg Dan Yakir 《Global Change Biology》2018,24(8):3486-3498
Carbonyl sulfide (COS) is a tracer of ecosystem photosynthesis that can advance carbon cycle research from leaf to global scales; however, a range of newly reported caveats related to sink/source strength of various ecosystem components hinder its application. Using comprehensive eddy‐covariance and chamber measurements, we systematically measure ecosystem contributions from leaf, stem, soil, and litter and were able to close the ecosystem COS budget. The relative contributions of nonphotosynthetic components to the overall canopy‐scale flux are relatively small (~4% during peak activity season) and can be independently estimated based on their responses to temperature and humidity. Converting COS to photosynthetic CO2 fluxes based on the leaf relative uptake of COS/CO2, faces challenges due to observed daily and seasonal changes. Yet, this ratio converges around a constant value (~1.6), and the variations, dominated by light intensity, were found unimportant on a flux‐weighted daily time‐scale, indicating a mean ratio of daytime gross‐to‐net primary productivity of ~2 in our ecosystem. The seasonal changes in the leaf relative uptake ratio may indicate a reduction in mesophyll conductance in winter, and COS‐derived canopy conductance permitted canopy temperature estimate consistent with radiative skin temperature. These results support the feasibility of using COS as a powerful and much‐needed means of assessing ecosystem function and its response to change. 相似文献
17.
Marguerite Mauritz Rosvel Bracho Gerardo Celis Jack Hutchings Susan M. Natali Elaine Pegoraro Verity G. Salmon Christina Schädel Elizabeth E. Webb Edward A. G. Schuur 《Global Change Biology》2017,23(9):3646-3666
Rapid Arctic warming is expected to increase global greenhouse gas concentrations as permafrost thaw exposes immense stores of frozen carbon (C) to microbial decomposition. Permafrost thaw also stimulates plant growth, which could offset C loss. Using data from 7 years of experimental Air and Soil warming in moist acidic tundra, we show that Soil warming had a much stronger effect on CO2 flux than Air warming. Soil warming caused rapid permafrost thaw and increased ecosystem respiration (Reco), gross primary productivity (GPP), and net summer CO2 storage (NEE). Over 7 years Reco, GPP, and NEE also increased in Control (i.e., ambient plots), but this change could be explained by slow thaw in Control areas. In the initial stages of thaw, Reco, GPP, and NEE increased linearly with thaw across all treatments, despite different rates of thaw. As thaw in Soil warming continued to increase linearly, ground surface subsidence created saturated microsites and suppressed Reco, GPP, and NEE. However Reco and GPP remained high in areas with large Eriophorum vaginatum biomass. In general NEE increased with thaw, but was more strongly correlated with plant biomass than thaw, indicating that higher Reco in deeply thawed areas during summer months was balanced by GPP. Summer CO2 flux across treatments fit a single quadratic relationship that captured the functional response of CO2 flux to thaw, water table depth, and plant biomass. These results demonstrate the importance of indirect thaw effects on CO2 flux: plant growth and water table dynamics. Nonsummer Reco models estimated that the area was an annual CO2 source during all years of observation. Nonsummer CO2 loss in warmer, more deeply thawed soils exceeded the increases in summer GPP, and thawed tundra was a net annual CO2 source. 相似文献
18.
GITTA LASSLOP MARKUS REICHSTEIN DARIO PAPALE† REW D. RICHARDSON‡ ALMUT ARNETH§ ALAN BARR¶ PAUL STOY GEORG WOHLFAHRT 《Global Change Biology》2010,16(1):187-208
The measured net ecosystem exchange (NEE) of CO2 between the ecosystem and the atmosphere reflects the balance between gross CO2 assimilation [gross primary production (GPP)] and ecosystem respiration (Reco). For understanding the mechanistic responses of ecosystem processes to environmental change it is important to separate these two flux components. Two approaches are conventionally used: (1) respiration measurements made at night are extrapolated to the daytime or (2) light–response curves are fit to daytime NEE measurements and respiration is estimated from the intercept of the ordinate, which avoids the use of potentially problematic nighttime data. We demonstrate that this approach is subject to biases if the effect of vapor pressure deficit (VPD) modifying the light response is not included. We introduce an algorithm for NEE partitioning that uses a hyperbolic light response curve fit to daytime NEE, modified to account for the temperature sensitivity of respiration and the VPD limitation of photosynthesis. Including the VPD dependency strongly improved the model's ability to reproduce the asymmetric diurnal cycle during periods with high VPD, and enhances the reliability of Reco estimates given that the reduction of GPP by VPD may be otherwise incorrectly attributed to higher Reco. Results from this improved algorithm are compared against estimates based on the conventional nighttime approach. The comparison demonstrates that the uncertainty arising from systematic errors dominates the overall uncertainty of annual sums (median absolute deviation of GPP: 47 g C m?2 yr?1), while errors arising from the random error (median absolute deviation: ~2 g C m?2 yr?1) are negligible. Despite site‐specific differences between the methods, overall patterns remain robust, adding confidence to statistical studies based on the FLUXNET database. In particular, we show that the strong correlation between GPP and Reco is not spurious but holds true when quasi‐independent, i.e. daytime and nighttime based estimates are compared. 相似文献