日光诱导叶绿素荧光和旱地作物生产力关联机制研究

Solar-induced chlorophyll fluorescence (SIF) provides a new approach to monitor the photosynthetic rate of crops and its response to environmental stress. Previous studies mainly focused on retrieving single-band SIF within the field of sensor and building the relationships between SIF and Gross Primary Production (GPP). Most of them had pointed out that drought stress may reduce SIF emitted from vegetation. However, several limitations still exist: information in complete SIF spectrum is not fully exploited, the link between total emitted SIF from plants and GPP is not built and the impact of drought severity on SIF-GPP relationship is largely unknown. By using the notch filters, this proposal plans to provide a more accurate estimation of the full broadband SIF emitted in a whole sphere at a leaf scale. At the same time, top-of-canopy (TOC) single-band SIF, GPP, chlorophyll fluorescence parameters (Chl FPs) and ecophysiological traits will also be measured in field condition. Our goal is to assess how drought stress affects SIF emission and Chl FPs at both leaf and canopy scale and how the SIF-GPP relationship responds to drought stress at the different growth stages of crops. The proposed indoor and field experiments should also provide a new approach to measure full SIF spectrum with higher accuracy and better assess the impact of water stress on SIF emission. Eventually, a SIF-based framework for yield forecasting at dryland croplands and quantitative analysis of drought risk will be established. Overall, the expected results will enhance our understanding of the link between SIF and crop ecophysiological characteristics in the arid regions of northwest China, and thus have the important scientific meaning for better-predicting crop production and accurately monitoring drought stress.

日光诱导叶绿素荧光（SIF）为认识农作物光合速率及其对胁迫因子的响应提供了新途径。当前研究多集中于特定方向视场角内提取的单波段SIF与总初级生产力（GPP）相关性分析，已经发现干旱胁迫能减少SIF发射，但缺乏在干旱环境下，叶片全波段SIF球面发射特征、全冠层SIF与GPP关联机制、以及SIF对不同干旱程度响应的深入研究。本项目利用透镜测量叶片全波段SIF的球面发射特征，结合SIF、GPP、叶绿素荧光参数以及生理生态特征的同步观测，探究在作物不同生长阶段，干旱对叶片及全冠层全波段SIF与GPP、荧光参数相关性的影响。研究将提高SIF野外观测和其对干旱响应的准确性，揭示旱区作物SIF与GPP的关联机制和驱动因素，建立基于SIF的作物GPP估算方法和定量化胁迫监测方案。预期结果将深化西北旱区SIF与作物生理生态特征耦合机制的认识，对提高作物生产力估算精度和干旱胁迫监测准确度有重要科学意义。

日光诱导叶绿素荧光(SIF)正成为研究植物初级生产力(GPP)的一个重要方向。目前研究多集中于冠层SIF观测和反演及其与GPP相关性的统计分析，缺乏多尺度荧光与光合内在关联机制及其对生物和环境响应的深入研究，难以解决二者相关性变异性大及胁迫下相关性弱的问题。本项目以我国西北旱区常见作物为研究对象，自行搭建光合、热耗散、荧光和光谱特征同步测量系统，在室内生物和环境因素控制下测量其叶片尺度同步响应特征，并在野外定位自动观测冠层SIF和GPP动态规律，结合光合荧光机理模型，深入发掘二者内在的联系和区别，实现基于SIF的GPP直接估算。具体开展了以下两方面的工作：1）设计了叶片尺度荧光强度和光合固碳同步观测系统，以便在恒定光强下，控制温度、CO2浓度和气孔导度等非光因素的变化，精准测量荧光强度和固碳速率。研究发现：在非光因素驱动下，SIF与光合固碳具有较好的协同变化，但SIF的变化幅度远小于固碳速率的变化幅度，因此观测精度对SIF研究植物生理变化至关重要。2）构建了一个SIF与GPP耦合模型，将SIF与植被的光合活动机理性地联系起来，通过叶片同步观测系统，解决了耦合模型中关键参数的取值问题，并估算热耗散和光系统２产率，实现了SIF直接估算冠层GPP。上述研究成果使得冠层尺度上从SIF机理性出发来估计GPP的能力提高，为区域和全球尺度上利用卫星SIF模拟碳吸收奠定基础。