基于碳水通量耦合原理改进Penman-Monteith蒸散发模型

陆地蒸散(ET)涵括地表和潮湿叶片的蒸发和植物的蒸散发,是陆地水循环的重要组成部分。Penman-Monteith方程是估算陆地蒸散的重要方法,方程中的叶片或冠层气孔导度是提高估算精度的关键因子。根据碳水循环的耦合原理,植物光合作用模型可用于估算叶片或冠层气孔导度。植物光合作用模型可分为三类:1)使用总冠层导度的大叶模型(BL),2)区别阴、阳叶冠层导度的双大叶模型(TBL),3)区别阴、阳叶叶片导度的双叶模型(TL)。与这三类光合作用模型相对应,衍生出基于不同导度计算方法的三种蒸散估算模型。三种蒸散模型之间的主要区别在于是否进行从叶片尺度到冠层尺度的气孔导度集成。这三种模型中,双叶模型使用叶片尺度的气孔导度,集成度最低。反之,大叶模型使用冠层尺度的气孔导度,集成度最高。由于在Penman-Monteith中,蒸腾和气孔导度之间的关系是非线性的,气孔导度的集合会导致负偏差。因此,与通量测量相比,大叶蒸散模型的估算偏差最大,而双叶蒸散模型的估算偏差最小。     

C3植物光合作用日变化的模拟

对前人光合作用-气孔导度耦合模型进行了修正,建立了光合作用-蒸腾作用-气孔导度的耦合模型,它概括了叶片上各主要物理过程和生理过程之间的相互联系和制约关系。 用数值方法研究了不同环境因子（太阳辐射、温度、湿度和风速等）对光合作用、蒸腾作用和气孔导度的日变化及中午降低（midday depression）的影响。 主要结果是:（1）当边界层导度减小时,光合“午睡”加剧,蒸腾作用减弱,但作为反馈调节,气孔导度增加。 （2）气孔导度的最适温度最低,光合作用次之,蒸腾作用最适温度最高。当光合作用中午受到高温的胁迫时,气孔导度下降的幅度最大,光合作用次之,蒸腾作用的降幅最小。一天中,气孔导度降低的持续时间最长,蒸腾作用降低的持续时间最短。（3）空气绝对湿度越低,气孔导度越低,光合午睡越明显。蒸腾作用则决定于饱和水汽压差(Vpd)和气孔导度两个因素的相反的作用。蒸腾作用随Vpd增加而增大,但Vpd超过一定值后,反而使蒸腾作用下降。 （4）当温度在光合最适温度以上时,太阳辐射的增加使叶温增加,引起光合“午睡”的加剧和气孔导度的降低。（5）ci/cs在中午的降低表明气孔的关闭是光合作用“午睡”现象的原因。     

淮北棉区花铃期冠层不同高度叶片光合特性的差异

基于多层二叶模型,在自然群体条件下,将棉花冠层分为上、中、下三层,研究淮北棉花花铃期冠层上、中、下层,阴叶（无直射光照射）与阳叶（有直射光照射）的光合特性的差异。结果表明,同一高度阳叶的光量子通量密度与光合速率显著大于阴叶;不同高度叶片光量子通量密度与光合速率均表现为上层阳叶〉中层阳叶〉下层阳叶,上层阴叶〉中层阴叶〉下层阴叶;上层阳叶气孔导度大于阴叶,中、下层阴、阳叶的气孔导度无显著差异;上部叶片气孔导度〉中部叶片〉下部叶片;同一高度阳叶胞间二氧化碳浓度显著小于阴叶,随着冠层深度（形态学自上而下）的增加,两者差异增大;不同高度叶片胞间二氧化碳浓度随着冠层深度的增加,呈增加趋势,阳叶差异不显著,阴叶差异显著。     

干旱环境下夏玉米各生育时期光响应特征

2011年6—9月在中国气象局河北固城生态试验站借助大型电动式防雨棚及人工灌溉, 开展水分影响夏玉米生长发育的田间试验。首先进行夏玉米叶片光合作用日变化和光合作用光响应曲线的观测,然后利用不同模型拟合光响应曲线确定最适模型并提取光合特征参数,探讨土壤水分条件对不同生育时期夏玉米叶片光合特性的影响规律。结果表明:土壤水份适宜时,玉米抽雄期的光合能力最强,重度干旱时,抽雄期的光合能力降低幅度也最大,其次为乳熟期、拔节期;直角双曲线修正模型最适合描述干旱环境下的玉米光合能力光响应过程,轻度干旱使各生育时期光饱和点及最大净光合速率下降,而对光补偿点量子效率和光补偿点的影响不明显; 重度干旱下各生育时期光饱和点、最大净光合速率较轻度干旱又进一步下降,同时各生育时期光补偿点量子效率也有明显下降,而光补偿点明显上升,表明玉米叶片的强光利用能力对干旱敏感,而它的弱光利用能力对干旱响应较迟钝。     

棉花阴、阳叶的气孔导度和光合作用观测对比及模型应用

以实验观测数据为基础,对棉花阳叶和阴叶光合速率、气孔导度的变化进行比较,通过双叶模型和大叶模型对冠层光合作用进行对比分析,结果表明,大叶模型的计算结果普遍高于双叶模型,总体高出13％。由此可见,过去在研究植被一大气碳交换中使用大叶模型估算植物光合作用会夸大碳汇的作用。     

利用遥感信息研究区域冬小麦气孔导度的时空分布

气孔导度是影响作物蒸散和作物的光合速率进而影响作物产量的重要因子。文中通过利用NOAA－AVHRR数据首次对华北平原典型区冬小麦气孔导度分布进行了研究,给出了华北平原典型区冬小麦不同生长季节的气孔导度空间分布状况,为进一步研究田间水分和作物蒸散对产量影响以及建立遥感作物水分胁迫生物量模型和监测不同生育期的农田缺水等提供依据。     

北方玉米冠层光合有效辐射垂直分布及影响因子分析

玉米冠层内光合有效辐射(PAR)的大小直接影响冠层内叶片的光合作用,进而影响玉米净第一性生产力或作物产量的准确评估。为弄清玉米冠层内光合有效辐射的分布规律及其影响因子,基于锦州玉米农田生态系统于2006年生育期的光合有效辐射观测数据和叶面积指数动态观测数据,对玉米冠层光合有效辐射的垂直分布特征及其影响因子进行了分析。结果表明:玉米冠层内不同垂直层次叶片的PAR分布随生育期变化显著,与叶面积指数呈显著的负相关(R2=0.89);玉米冠层光合有效辐射的消光系数K值在生育期呈动态变化,约为0.76,且表现为苗期较大、生育后期较小。分析表明,在进行光合有效辐射及与此密切相关的光合作用模拟时,应考虑消光系数的动态变化。     

相对湿度对黄瓜叶片光合特性的影响

以黄瓜“津优1号”为试材,于2011年4月在南京信息工程大学进行人工环境控制试验,设计8个相对湿度梯度,用LI 6400进行光合参数的测定,系统研究不同相对湿度处理对黄瓜叶片光合特性的影响。结果表明：黄瓜叶片的净光合速率和胞间CO2浓度随着相对湿度的减小而降低;气孔导度、蒸腾速率和叶片的水分利用效率在相对湿度为75%时达到最大;而气孔限制值在相对湿度为75%时降到最低;黄瓜叶片最大光合作用速率（Pmax）与空气相对湿度呈指数关系：Pmax=22375e189085fRH;随空气相对湿度的减小,黄瓜叶片的表观量子效率、光饱和点均降低,而光补偿点增加;相关分析表明,净光合速率与叶面水汽压差呈负相关,而与气孔导度、胞间CO2浓度、相对湿度、蒸腾速率均呈正相关,且相关性均达到极显著水平。     

北方玉米冠层光合有效辐射垂直分布及影响因子分析

玉米冠层内光合有效辐射（PAR）的大小直接影响冠层内叶片的光合作用,进而影响玉米净第一性生产力或作物产量的准确评估。为弄清玉米冠层内光合有效辐射的分布规律及其影响因子,基于锦州玉米农田生态系统于2006年生育期的光合有效辐射观测数据和叶面积指数动态观测数据,对玉米冠层光合有效辐射的垂直分布特征及其影响因子进行了分析。结果表明：玉米冠层内不同垂直层次叶片的PAR分布随生育期变化显著,与叶面积指数呈显著的负相关（R2=0.89）;玉米冠层光合有效辐射的消光系数K值在生育期呈动态变化,约为0.76,且表现为苗期较大、生育后期较小。分析表明,在进行光合有效辐射及与此密切相关的光合作用模拟时,应考虑消光系数的动态变化。     

寡照对设施黄瓜光合特性的影响研究

为研究寡照对设施黄瓜苗期及花果期叶片光合速率的影响,于2012年2—4月份在章丘伟丽种苗基地设计不同程度寡照处理试验。结果表明：随着寡照天数的增加,黄瓜叶片PRD-V,LsD-V,TrD-V和CD-V均呈上升趋势,差值越大,寡照对黄瓜叶片光合速率、气孔限制值、蒸腾速率和气孔导度的影响越大。寡照处理1～7d,黄瓜叶片PRD-V,TrD-V和CD-V迅速增大,寡照处理7d后,黄瓜叶片PRD-V,TrD-V和CD-V缓慢增大,并趋于稳定。寡照7d可视为设施黄瓜发生寡照胁迫的临界值,苗期黄瓜叶片光合特性受寡照影响大于花果期。     

Observations of leaf stomatal conductance at the canopy scale: An atmospheric modeling perspective

Plant stomata play a key role in the redistribution of energy received on vegetated land into sensible and latent heat. As a result, they have a considerable impact on the atmospheric planetary boundary layer, the hydrologic cycle, the climate, and the weather. Current parameterizations of the stomatal mechanism in state-of-the-art atmospheric models are based on empirical relations that are established at the leaf scale between stomatal conductance and environmental conditions. In order to evaluate these parameterizations, an experiment was carried out on a potato field in New Jersey during the summer of 1989. Stomatal conductances were measured within a small homogeneous area in the middle of the potato field and under a relatively broad range of atmospheric conditions. A large variability of stomatal conductances was observed. This variability, which was associated with the variability of micro-environmental and physiological conditions that is found even in a homogeneous canopy, cannot be simulated explicitly on the scale of a single agricultural field and,a fortiori, on the scale of atmospheric models. Furthermore, this variability could not be related to the environmental conditions measured at a height of 2 m above the plant canopy simultaneously with the conductances, reinforcing the concept of scale decoupling suggested by Jarvis and McNaughton (1986) and McNaughton and Jarvis (1991). Thus, for atmospheric modeling purposes, a parameterization of stomatal conductance at the canopy scale using external environmental forcing conditions seems more appropriate than a parameterization based on leaf-scale stomatal conductance, as currently adopted in state-of-the-art atmospheric models. The measured variability was characterized by a lognormal probability density function (pdf) that remained relatively stable during the entire measuring period. These observations support conclusions by McNaughton and Jarvis (1991) that, unlike current parameterizations, a parameterization of plant stomata applied on a field (or larger) scale, might not require inclusion of the complex relations found at the leaf scale between stomata and their microenvironment.     

非直角双曲线光合模型的积分及参数灵敏度分析

非直角双曲线单叶光合模型对光合反应有更灵敏的响应。将它对叶面积积分，并用于大田干物质计算。其精度比用直角双曲线型的叶面积积分模式有所提高。对光合参数作了灵敏度试验，并指出育种和数值模拟试验中应注意的问题。     

The Simulation of the Opposing Fluxes of Latent Heat and CO<Subscript>2</Subscript> over Various Land-Use Types: Coupling a Gas Exchange Model to a Mesoscale Atmospheric Model

A mesoscale meteorological model (FOOT3DK) is coupled with a gas exchange model to simulate surface fluxes of CO₂ and H₂O under field conditions. The gas exchange model consists of a C3 single leaf photosynthesis sub-model and an extended big leaf (sun/shade) sub-model that divides the canopy into sunlit and shaded fractions. Simulated CO₂ fluxes of the stand-alone version of the gas exchange model correspond well to eddy-covariance measurements at a test site in a rural area in the west of Germany. The coupled FOOT3DK/gas exchange model is validated for the diurnal cycle at singular grid points, and delivers realistic fluxes with respect to their order of magnitude and to the general daily course. Compared to the Jarvis-based big leaf scheme, simulations of latent heat fluxes with a photosynthesis-based scheme for stomatal conductance are more realistic. As expected, flux averages are strongly influenced by the underlying land cover. While the simulated net ecosystem exchange is highly correlated with leaf area index, this correlation is much weaker for the latent heat flux. Photosynthetic CO₂ uptake is associated with transpirational water loss via the stomata, and the resulting opposing surface fluxes of CO₂ and H₂O are reproduced with the model approach. Over vegetated surfaces it is shown that the coupling of a photosynthesis-based gas exchange model with the land-surface scheme of a mesoscale model results in more realistic simulated latent heat fluxes.     

碳四植物光合生化机理模型的叶片含水量修正

叶片光合作用的准确模拟对陆地生态系统模型及全球变化对植被影响研究具有重要意义。水分是影响光合作用的重要因素,目前研究多采用土壤含水量表示,而非直接起作用的叶片含水量,这限制了光合作用的准确模拟。以玉米为研究对象,利用2014年6—10月中国气象科学研究院固城生态与农业气象试验站玉米6个水分梯度持续干旱试验数据,结合光合生化机理模型,定量研究最大羧化速率与叶片含水量的关系。结果表明:两者呈显著二次曲线关系,其拟合方程的决定系数达0.88;参数不同时,最大羧化速率的绝对值不同,但归一化后的叶片含水量修正函数与参数无关,当叶片含水量为80%左右时,其修正函数值为1,当叶片含水量降至70%左右时,其修正函数值为0。研究从叶片含水量影响方面完善了碳四植物光合生化机理模型,可为进一步提高光合作用模拟的准确性和玉米干旱监测预警提供参考。     

Influence of leaf water potential on diurnal changes in CO2 and water vapour fluxes

Mass and energy fluxes between the atmosphere and vegetation are driven by meteorological variables, and controlled by plant water status, which may change more markedly diurnally than soil water. We tested the hypothesis that integration of dynamic changes in leaf water potential may improve the simulation of CO₂ and water fluxes over a wheat canopy. Simulation of leaf water potential was integrated into a comprehensive model (the ChinaAgrosys) of heat, water and CO₂ fluxes and crop growth. Photosynthesis from individual leaves was integrated to the canopy by taking into consideration the attenuation of radiation when penetrating the canopy. Transpiration was calculated with the Shuttleworth-Wallace model in which canopy resistance was taken as a link between energy balance and physiological regulation. A revised version of the Ball-Woodrow-Berry stomatal model was applied to produce a new canopy resistance model, which was validated against measured CO₂ and water vapour fluxes over winter wheat fields in Yucheng (36°57′ N, 116°36′ E, 28 m above sea level) in the North China Plain during 1997, 2001 and 2004. Leaf water potential played an important role in causing stomatal conductance to fall at midday, which caused diurnal changes in photosynthesis and transpiration. Changes in soil water potential were less important. Inclusion of the dynamics of leaf water potential can improve the precision of the simulation of CO₂ and water vapour fluxes, especially in the afternoon under water stress conditions.     

陆面模式的植物叶光合生理的数值模拟试验及分析

根据C3、C4植物生态生理过程中植物叶水平的光合同化机制过程和植物叶片尺度的光合作用限制函数方程。采用单叶光合作用模式进行C3、C4植物光合模拟试验,模拟不同环境影响因子对C3、C4植物光合作用的影响。结果表明,植物叶尺度光合作用模型能较好地模拟不同环境影响因子下的C3、C4植物光合作用状况。本文依据C3、C4植物光合生理特性进一步分析植物光合作用的三个限制函数方程在C3、C4植物光合的不同作用,揭示吸收光合有效辐射(PAR)、叶内温度(Tc)和CO2浓度(Ci)的敏感性。结果可用于植被—大气相互作用的能量和碳同化过程的物质交换研究。