基于叶绿素遥感的植被光合速率模拟研究

Vegetation maximum photosynthetic carboxylation rate (Vcmax) is one of the important parameters in simulating GPP (Gross Primary Productivity). However, spatio-temporal variations of Vcmax are rarely considered, which increase the uncertainty when estimating GPP. Recent studies have shown that chlorophyll and leaf nitrogen are highly coupled and Vcmax is closely related to nitrogen content in Rubisco. Therefore, the accuracy of the simulation results will be improved if the chlorophyll retrieved from remote sensing data is involved in the ecosystem model, since chlorophyll could reflect the spatio-temporal variations of Vcmax. However, the relationship between chlorophyll and leaf nitrogen and the assigned ratio of leaf nitrogen to Rubisco are not clear, both of which are lack of reasonable simulation method. Address this problem, this project will analyze the relationship between nitrogen content in Rubisco and chlorophyll based on observation data, construct a model on estimating Vcmax driven by remote sensing data of chlorophyll content; simulate spatial and temporal variations of Vcmax on a regional scale; and at last evaluate the effect of coupling chlorophyll content from remote sensing data on simulating GPP. This proposal has great scientific significance to understand carbon and nitrogen coupling process of terrestrial ecosystem, through involving remotely sensed chlorophyll into the ecosystem model.

最大光合羧化速率（Vcmax）是植被总初级生产力（GPP）模拟的重要参数，但当前生态系统过程模型没有考虑其时空变化，导致GPP的估算结果存在较大的不确定性。近年来的研究表明，叶绿素与叶片氮高度耦合，Vcmax与叶片Rubisco酶中氮含量紧密联系。因此，在生态系统模型中引入遥感反演的叶绿素含量信息就有可能顾及Vcmax的时空变化，提高模拟结果的可靠性。但是，叶绿素与叶片氮之间关系以及叶片氮分配到Rubisco酶的比例尚不完全清楚，缺乏可靠的模拟方法。针对这一问题，本项目将基于观测数据，分析Rubisco酶中氮含量与叶片叶绿素含量之间关系；建立基于叶绿素含量遥感数据的Vcmax估算方法，进行Vcmax的区域制图并分析其时空变化特征；评价耦合叶绿素含量遥感数据对改进生态系统模型GPP模拟的作用。成果对充分利用遥感信息深入理解陆地生态系统碳氮耦合过程具有重要的科学意义。

最大光合羧化速率（Vcmax）是植被总初级生产力（GPP）模拟的重要参数，但当前生态系统过程模型没有考虑其时空变化，导致GPP的估算结果存在较大的不确定性。本研究基于观测数据，分析叶片Rubisco含量与叶片叶绿素含量之间关系；建立基于叶绿素含量遥感数据的Vcmax估算方法，进行Vcmax的区域制图并分析其时空变化特征；评价耦合叶绿素含量遥感数据对改进生态系统模型GPP模拟的作用。研究结果显示在不同生态系统中叶片叶绿素和Rubisco酶都具有较强的线性关系，平均R2达到0.7以上。在C3植被类型中，叶绿素和Rubisco酶的线性关系没有显著差异。而这一关系在C3植被和C4植被之间却差异显著。此外，长时间序列的观测数据显示叶绿素和Rubisco酶在整个生长季都保持较强的线性关系，且这一关系与不同生态系统中的关系保持一致。结合一种半机理模型，本研究建立了利用叶片叶绿素含量估算Vcmax25的方法。通过该方法估算的Vcmax25精度较高，在站点尺度和全球尺度的验证中表现出色。Vcmax25具有明显的时间序列变化特点。通过耦合本研究估算的全球Vcmax25改进当前模型中Vcmax25的参数化方案, GPP模拟结果的RMSE下降了约9%。