Photosynthetic phenology is an important indicator of annual gross primary productivity (GPP). Assessing photosynthetic phenology remotely is difficult for evergreen conifers as they remain green year-round. Carotenoid-based vegetation indices such as the photochemical reflectance index (PRI) and chlorophyll/carotenoid index (CCI) are promising tools to remotely track the invisible phenology of photosynthesis by assessing carotenoid pigment dynamics. PRI, CCI and the near-infrared reflectance of vegetation (NIRV ) index may act as proxies of photosynthetic efficiency (ɛ), an important parameter in light-use efficiency models, or direct proxies of photosynthesis. To understand the physiological mechanisms reflected by PRI and CCI and the ability of vegetation indices to act as proxies of photosynthetic activity for estimating GPP, we measured leaf pigment composition, PRI, CCI, NIRV and photosynthetic activity at the leaf and canopy scales over 2 years in an evergreen and mixed deciduous forest. PRI and CCI captured the large seasonal carotenoid/chlorophyll ratio changes and good relationships were observed between PRI-ɛ and CCI-photosynthesis and NIRV -photosynthesis. PRI-, CCI- and NIRV -based models effectively tracked observed seasonal GPP. We propose that carotenoid-based and near-infrared reflectance vegetation indices may provide useful proxies of photosynthetic activity and can improve remote sensing-based models of GPP in evergreen and deciduous forests.

中文翻译：

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在温带常绿混交落叶林中使用类胡萝卜素敏感和近红外反射植被指数跟踪光合作用的物候。

光合物候学是年度总初级生产力（GPP）的重要指标。对于常绿针叶树来说，由于它们一年四季都保持绿色，因此很难对其光合物候进行远程评估。基于类胡萝卜素的植被指数，例如光化学反射率指数（PRI）和叶绿素/类胡萝卜素指数（CCI），是通过评估类胡萝卜素色素动力学来远程跟踪光合作用的隐形物候的有前途的工具。PRI，CCI和植被的近红外反射率（NIRV）可能充当光合作用效率（ɛ）的代理，它是光利用效率模型中的重要参数，或者是光合作用的直接代理。要了解PRI和CCI反映的生理机制，以及植被指数充当光合作用代理估算GPP的能力，我们在常绿和混合落叶林中的2年内测量了叶片色素组成，PRI，CCI，NIRV和叶片和冠层尺度的光合活性。PRI和CCI捕获了较大的季节性类胡萝卜素/叶绿素比率变化，并且在PRI-ɛ和CCI-光合作用与NIRV-光合作用之间观察到良好的关系。基于PRI，CCI和NIRV的模型有效地跟踪了观测到的季节性GPP。我们建议基于类胡萝卜素和近红外反射植被指数可以提供光合作用的有用代理，并可以改善常绿和落叶林中GPP的基于遥感的模型。PRI和CCI捕获了较大的季节性类胡萝卜素/叶绿素比率变化，并且在PRI-ɛ和CCI-光合作用与NIRV-光合作用之间观察到良好的关系。基于PRI，CCI和NIRV的模型有效地跟踪了观测到的季节性GPP。我们建议基于类胡萝卜素和近红外反射植被指数可以提供光合作用的有用代理，并可以改善常绿和落叶林中GPP的基于遥感的模型。PRI和CCI捕获了较大的季节性类胡萝卜素/叶绿素比率变化，并且在PRI-ɛ和CCI-光合作用与NIRV-光合作用之间观察到良好的关系。基于PRI，CCI和NIRV的模型有效地跟踪了观测到的季节性GPP。我们建议基于类胡萝卜素和近红外反射植被指数可以提供光合作用的有用代理，并可以改善常绿和落叶林中GPP的基于遥感的模型。