不同生态系统日光诱导叶绿素荧光与植被生产力的关系研究

The gross carbon uptake of terrestrial vegetation through photosynthesis, or gross primary production (GPP), is the primary driver of the carbon cycle in the Earth system. Ironically, our current knowledge of global GPP and its main environmental controls is highly uncertain. Given that no large-scale measurements of GPP are possible, satellite-based observations of canopy greenness have been used in the last years to gain insights into global terrestrial photosynthetic mechanisms. However, the approaches present inherent limitations to provide an accurate description of ecosystem functioning: satellite observations of greenness lack a direct link to a highly dynamical process such as photosynthesis. By contrast, recent advances in spectroscopy have enabled the space-based monitoring of the sun-induced chlorophyll fluorescence (SIF) signal emitted from terrestrial plants during photosynthesis, an emission intrinsically linked to plant biochemistry. However, the relationship between SIF and photosynthesis and what factors and how influence their relationship are not clear, and there is a distinct differences between them across biomes. This project intends to derive and exploit unique spectroscopic measurements of SIF and other vegetation parameters from long-term multi-directional canopy-level field measurements in order to study the relationships between SIF and gross carbon fluxes for different biomes. The underlying mechanics of the differences between SIF and GPP across different plant functional types will be investigated, and then a unique SIF-based model for GPP will be derived for all the biomes. Finally, we will model regional GPP with fluorescence as observed by new satellite sensors (OCO2 and TROPOMI) which provide a 100-fold increase in spatial and temporal resolution with respect to the existing satellite used for SIF monitoring. Our results will improve global estimates of carbon fluxes by direct measurements of photosynthetic activity from space.

植被总初级生产力（GPP）是全球碳循环的最大碳通量，目前卫星遥感观测是GPP估算的主要手段之一，但基于“绿度”观测的植被指数仅反映植物的潜在光合作用状况，而叶绿素荧光能直接反映植物实际光合作用的状况，是估算GPP更直接的手段。日光诱导叶绿素荧光（SIF）已在多个卫星传感器上反演得到，利用其估算区域及全球尺度GPP成为现实，但不同时空尺度上SIF与GPP关系的变化特征尚不明确，不同生态系统间二者关系差异机制也不清楚。本研究选择多种生态系统，进行植被叶绿素荧光和涡度通量同步观测及模型模拟，探索不同时相上冠层SIF与GPP关系的变化规律及影响因素，定量分析不同生态系统间二者关系差异原因，构建适合不同生态系统的叶绿素荧光遥感GPP估算模型，结合高空间分辨率卫星荧光遥感数据，进行区域GPP估算。该研究可为基于叶绿素荧光遥感的光合作用探测提供支撑，提高碳通量遥感反演精度。

植被叶绿素荧光遥感是资源与环境遥感领域近年来兴起的新兴方向之一，尤其是为陆地生态系统GPP估算提供了新的思路和方法。植被叶绿素荧光能直接反映植物实际光合作用的动态变化，是估算GPP更直接的手段。日光诱导叶绿素荧光（SIF）已在多个卫星传感器上反演得到，利用其估算区域GPP成为现实，但光合作用与SIF的关系时空尺度变化特征还不明确，不同生态系统间其关系差异机制也不清楚。申请人在本项目的支持下，针对研究的科学问题，开展了大量的观测、分析与研究工作，在如下几个方面取得了系统的研究成果：（I）研制了植被冠层SIF自动观测系统，推动成立了中国生态系统光谱观测网络ChinaSpec；（II）厘清了不同时相尺度上植被冠层SIF和GPP耦合关系变化的规律；（III）建立了植被冠层叶绿素总激发荧光的估算方法；（IV）构建了考虑植被冠层结构和光合差异的叶绿素荧光遥感估算GPP模型；（V）开发面向陆面模式的全球尺度叶绿素荧光模型BEPS-SIF。在项目的支持下在国内外期刊上共发表学术论文17篇，其中Nature Ecology & Evolution、Remote Sensing of Environment、Global Change Biology、Geophysical Research Letters、Agricultural and Forestry Meteorology等高水平论文14篇，获得发明专利授权1项，软件著作权2项，指导博士后1名，培养毕业研究生4名。开展了广泛的国内外交流与合作研究，取得明显效果，合作研究正深入推进。研究成果进一步丰富了植被叶绿素荧光遥感的理论基础，能为进一步利用叶绿素荧光遥感数据提供了实验与理论支撑。