【作者】 张雪松；

【导师】 申双和；

【作者基本信息】 南京信息工程大学 ， 农业气象、生态环境气象， 2009， 博士

【摘要】 陆地生态系统的碳、水循环是全球变化科学的热点和核心问题。陆地生态系统碳循环包括植物的光合作用、自养呼吸作用及异养呼吸作用三个过程,其中光合作用通过植物的气孔调节行为,与控制水分散失的蒸腾作用相联系,构成了土壤—植物—大气系统中相互作用、互为反馈的碳、水循环过程,它们的动态变化将对气候系统产生重大影响。农田生态系统是受人类活动干扰最大的陆地生态系统,也是气候变化的主要承受者,对农田生态系统中碳、水循环机理过程、变化趋势及其对环境响应的综合研究,将有助于了解农田生态系统缓解全球CO₂浓度上升的潜在可能性及其对全球变化的贡献,并为构建生态系统尺度碳、水循环模型奠定基础。本研究以冬小麦为研究对象,利用LI-6400R光合—蒸腾测量系统、LI-6400-09土壤呼吸室和禹城生态试验站涡度相关系统等高精度仪器设备,对2007年和2008年小麦拔节至乳熟期间涉及碳、水循环过程的叶片光合—蒸腾作用、土壤呼吸作用及相关农田气象要素和植被特征进行了野外试验测定和分析,在试验观测基础上提取了重要生理参数,建立了基于过程的农田与大气间物质输送和能量交换的多层—双叶模型,并对2008年试验期间冠层上方碳通量特征进行了模拟,试验分析和模拟的主要结论如下:1.叶片水平光合—蒸腾过程的碳、水循环特征:不同生育期中测定的不同层次阴、阳叶片具有各自明显的净光合速率、蒸腾速率和水分利用效率日变化特征,这是包括光合有效辐射、气孔导度、CO₂浓度、温度等影响因子在内的综合作用的结果,进行气孔限制分析是解释日变化规律的有效方法;随光强增加,各层次叶片净光合速率均呈直角双曲线增加,蒸腾速率呈直线增加,在两者共同影响下,叶片水平水分利用效率亦呈直角双曲线增加,且存在“光饱和”特征;随CO₂浓度增加,各层次叶片净光合速率呈直角双曲线形式增加,同时气孔导度下降导致蒸腾速率呈波浪式下降,两者共同使叶片水平水分利用效率提高,蒸腾速率对由CO₂浓度变化而引起的气孔运动的响应比净光合速率快。2.土壤呼吸过程的碳循环特征及根呼吸的贡献:不同组分土壤呼吸存在明显日变化和季节变化特征,其中季节变化是以温度起重要作用并受根生物量协同影响的综合结果,5-10cm土壤温度大约可以解释不同组分土壤呼吸季节变化的49%～65%,土壤中根生物量大约可以解释土壤呼吸季节变化的44%;综合根去除法和根生物量外推法两种方法估算的研究期间根呼吸对土壤总呼吸的贡献为32%～45%。3.农田生态系统尺度的能量平衡与碳、水循环特征:植物以叶片为生命活动的基本单元,在生态系统尺度通过湍流交换等形式推动物质（碳、水）循环流动,并与系统中驱动物质循环的能量传输密不可分。本研究分析结果表明,利用涡度相关技术直接测定的农田生态系统尺度能量和物质通量,具有明显的日变化和季节变化特征,但涡度相关技术与常规观测技术相比存在低估趋势。利用生态系统水分利用效率（WUEe）可以衡量生态系统尺度碳、水循环关系,其日变化特征随生育期不同而不同。将生态系统水平与叶片水平的水分利用效率日均值进行比较,前者较后者高,原因可能与研究时对不同尺度采用了不能直接可比的不同的测定方法有关,也可能与涡度相关技术对能量通量的低估有关。4.多层—双叶模型对冠层上方碳通量的模拟:综合考虑农田水、热因子及叶片氮含量的非线性垂直分布对碳、水循环的影响,将农田按植株高度分为上、中、下三层,并通过叶片集聚指数计算阴、阳叶面积以区分叶片的空间分布受光状态,建立了均匀农田与大气间物质输送和能量交换的多层—双叶模型,对农田冠层上方基于光合—呼吸的碳循环过程进行了模拟应用研究。利用涡度相关碳通量观测数据对模型模拟能力的检验结果表明,模拟值大约可以解释实测值的78.5%,拟合程度较高,模拟的CO₂通量日变化特征在晴天的日间比在阴雨天和夜间的效果好。在叶片非随机分布的密集农田中,阴叶对GPP的贡献率在35.7%左右,说明阴叶对生产力的贡献也很重要,分层模拟显示,作物最终产量的形成主要依赖上层叶片,对GPP贡献率占80%以上,模型估算的试验期间冬小麦NPP累计约为626.3gC·m^-2。更多还原

【Abstract】 Carbon cycle and water cycle of terrestrial ecosystem have become two hot issues and kernel questions in global change science.There are three processes in carbon cycle of terrestrial ecosystem include plant photosynthsis,autotrophic respiration and heterotrophic respiration,among them,plant photosynthsis can connect by stomatal behavior with transpiration which can control leaf water dissipation,and then the interactional coupling cycle of carbon and water is formed in soil-plant-atmosphere system,and every dynamic change in coupling cycle will have a significant impact on the climate system. Agro-ecosystem is affected most seriously by human activities,also is the main accepter for climate change,the comprehensive study on mechanisms process,variation tendency and response to environment of carbon and water cycle are helpful to understand the potential probability of easing global CO₂ concentration increase in agro-ecosystem and its contribution to global change,and also can lay the foundation for building the coupling model of carbon-water cycle at ecosystem-scale.In this study,leaf photosynthesis-transpiration rate,soil respiration rate and related meteorological factors in typical winter wheat agro-ecosystem were measured by using LI-6400R portable photosynthesis-transpiration system,LI-6400R-09 soil CO₂ flux chamber and eddy covariance system et al.at the Yucheng Comprehensive Experimental Station of the Chinese Academy of Sciences during the main growing season in 2007 and 2008.We analyzed and discussed the characteristics of cycle of carbon and water,and after having obtained important physiological parameters based on field experiment,a process-based, multilayer two-leaf model which calculates energy and material cycle separately for sunlit and shaded leaves was developed,then characteristic of CO₂ fluxes above the canopy was simulated.The main results are as follows:1.Characteristics of carbon and water cycle in the relationship of leaf photosynthesis -stomatal conductance-transpiration.It is quite different for leaf net photosynthesis rate（Pn） measured in different height layer after separated into sunlit and shaded leaves in different growing stage,and so transpiration rate（Tr） and water use efficiency（WUE）,and these resulted from the joint effects of photosynthetically active radiation（PAR）,stomatal conductance,CO₂ concentration,temperature and other factors.Stomatal limited analysis is an effective method to explain the daily variation regularity;With PAR increasing,Pn presented a rectangular hyperbolic curve increase,and Tr was linear rise,then leaf level WIdE showed a rectangular hyperbolic curve increases with " light saturation" under the influence of Pn and Tr;With the CO₂ concentration enrichment,Pn displayed a rectangular hyperbolic increase,but Tr decreased wavily result from stomatal conductance change,then caused an increase in leaf level WUE,and the response of Tr to stomatal movement which caused by CO₂ concentration change was faster than the response of Pn.2.Characteristics of carbon cycle in the process of soil respiration and the contribution of root respiration,each of the different components of soil respiration had a clear diurnal variation and a seasonal variation,temperature played an important role and root biomass had a synergistic effect to the seasonal variation,5-10cm soil temperature can explaine about 49%～65%of the seasonal variation while root biomass about 44%.Integrated the root exclusion method and the root biomass extrapolation method,this study considers the contribution of root respiration to total soil respiration of winter wheat has a range from 32%～45%.3.Characteristics of energy balance and carbon,water cycle at Agro-ecosystem-scale. Leaf is the basic unit for plant vital activities,which can drive material（carbon and water） circular flow through turbulent exchange and there has a very close correlation between energy transmission and material cycle in SPAC.In this study,Ago-ecosystem-scale energy and material fluxes showed significant diurnal and daily variations when they were measured directly using the eddy covariance（EC） technique,while,compared to conventional observation methods,EC presented an underestimation trend.The ecosystem water use efficiency（WUEe） can describe the relationship of carbon and water cycle at Agro-ecosystem-scale,and the diurnal variation of WUEe was different in April and May. Also,we found that the daily average value of WUEe always higher than that of leaf level WUE,one reason maybe lie in that they can not be compared directly for using two kinds of different measurement methods,the other reason may be associated with the energy fluxes underestimate by EC technology.4.Simulation of winter wheat canopy CO₂ fluxes by a multiplayer two-leaf model. Considering many biophysics processes such as the atmosphere,hydrology,plant leaf N content et al.a multiple layer,two-leaf canopy model for predicting of mass transportation and energy exchange between plant canopies and the atmosphere has developed after dividing the canopy height into three layers（top,middle and bottom）,and the sunlit and shaded leaf area index was computed respectively at different layers through introducing a foliage clumping index,it is important to distinguish the spatial light distribution and so leaf photsynthesis.The simulation results showed that the model performed well after compareing with eddy covariance CO₂ fluxes data,the modeled fluxes can explain about 78.5%of the measured in this study,the modeled diurnal variation of CO₂ fluxes have a higher precision at fine daytime than cloudy and nighttime.The clumped architecture of winter wheat canopy makes the stratification between sunlit and shaded leaves essential because the fractin of shaded leaves is much larger in clumped canopy than in random canopy,and shaded leaves play an importance role of about 35.7%to total gross primary productivity（GPP） in this study, while the leaves in top layer is about 80%,the modeled total net primary productivity（NPP） during the study period is 626.3gC·m^-2.更多还原