双叶模型在冬小麦田冠层CO2通量多层模拟中的应用

An application of the two-leaf model in multilayer simulation for winter wheat canopy CO2 fluxes

中文关键词:  CO2通量， 双叶模型， 多层模拟， 冬小麦冠层， 农田生态系统

英文关键词:CO2 fluxes, Two leaf model, Multilayer simulation, Winter wheat canopy, Field ecosystem

中文摘要:

      综合考虑农田生态系统中水、热、CO2输送所涉及的大气、水文、生物等生物物理过程，以Farquhar等提出的叶片尺度光合作用生物化学过程机理模型为理论基础，对其进行空间尺度扩展，并改进冠层分层方法，建立了均匀农田与大气之间物质输送和能量交换的多层模式，在模式中运用双叶模型，同时考虑叶片氮素水平垂直差异，对2008年4—5月华北平原冬小麦生长旺季农田生态系统中冠层CO2通量进行了模拟研究，并利用涡度相关观测的通量数据对模型的有效性加以验证，结果表明：在冠层多层空间，小麦拔节至孕穗期和开花至乳熟期叶片氮含量随冠层高度的衰减系数分别为0.793（R2=0.698）和1.374（R2=0.728），冠层内叶片氮含量的空间分布可以用以相对累积叶面积指数为自变量的函数来描述；模型分别计算各层阴、阳叶的光截取、气孔传导、光合作用等，最终计算冠层上方CO2通量，冬小麦农田净生态系统生产力模拟值与实测值相关显著（R2=0.78），模拟的CO2通量日变化特征晴天昼间比阴雨天和夜间的效果好；在考虑丛聚影响的叶片非随机分布的密集农田中，阴叶对总初始生产力的贡献率在35.7%左右，对生产力贡献很重要。分层统计显示，作物最终产量的形成主要依赖上部叶片，对总初始生产力贡献率在80%以上，模型估算的试验期冬小麦净初始生产力累计约为626.3 g/m2

英文摘要:

      Considering atmospheric, hydrological, biological, and other biophysical processes in a soil plant atmosphere system, upscaling the mechanism model of photosynthetic biochemical processes established by Farquhar from leaf to canopy scale, and improving the canopy layered method, a multilayer, two-leaf model for the estimation of mass transfer and energy exchange between plant canopies and the atmosphere was developed, which combined the vertical variation of nitrogen content in the leaves， and could tell fluxes of water, heat and CO2 above the canopy after calculating the intercepted irradiance, stomatal conductance and photosynthesis of sunlit and shaded leaves separately in each layer. Based on the simulations using this an exponential function of nitrogen level in leaves was established and presented, changing with the height of canopy or the relative cumulative leaf area index and relating to the nitrogen attenuation coefficient of kn. This model was applied to modeling of the CO 2 fluxes for winter wheat canopy at the Yucheng Comprehensive Experimental Station of the Chinese Academy of Sciences during April to May in 2008 with the result that the attenuation coefficients of kn are 0.792 （R2=0.698） and 1.374 （R2=0.728） during the periods of jointing to booting and anthesis to milky maturity, respectively. When using the eddy covariance flux data to verify the validity of the model, it is seen that there is a close relationship between the modeled net ecosystem productivity (NEP) and the measured with R2=0.78, and that the modeled hourly CO2 fluxes indicate better agreement with measurements on clear days than on cloudy days and at nights. The shaded leaves played an important role in the productivity with the contributing rate accounting for 35.7% of the total gross primary productivity (GPP). The leaves of the upper canopy dominated the contribution to the final yield, accounting for more than 80% of the GPP. The modeled total net primary productivity (NPP) was 626.3 g/m2 during the experimental period.