Comparative Analysis on the Estimation of Diurnal Solar-Induced Chlorophyll Fluorescence Dynamics for a Subtropical Evergreen Coniferous Forest

Jinghua Chen,Xiaobo Wang,Junbang Wang,Pengyuan Wang,Fengting Yang,Bin Chen,Kai Zhu,Yue Li,Yuanyuan Liu,Mei Huang,Shaoqiang Wang,Li Ma,Muhammad Amir,Zhaosheng Wang

doi:10.3390/rs13163143

Abstract

Solar-induced chlorophyll fluorescence (SIF) is considered as a prospective indicator of vegetation photosynthetic activity and the ecosystem carbon cycle. The current coarse spatial-temporal resolutions of SIF data from satellite missions and ground measurements still cannot satisfy the corroboration of its correlation with photosynthesis and carbon flux. Practical approaches are needed to be explored for the supplementation of the SIF measurements. In our study, we clarified the diurnal variations of leaf and canopy chlorophyll fluorescence for a subtropical evergreen coniferous forest and evaluated the performance of the canopy chlorophyll concentration (CCC) approach and the backward approach from gross primary production (GPP) for estimating the diurnal variations of canopy SIF by comparing with the Soil Canopy Observation Photosynthesis Energy (SCOPE) model. The results showed that the canopy SIF had similar seasonal and diurnal variations with the incident photosynthetically active radiation (PAR) above the canopy, while the leaf steady-state fluorescence remained stable during the daytime. Neither the CCC nor the raw backward approach from GPP could capture the short temporal dynamics of canopy SIF. However, after improving the backward approach with a correction factor of normalized PAR incident on leaves, the variation of the estimated canopy SIF accounted for more than half of the diurnal variations in the canopy SIF (SIF687: R2 = 0.53, p < 0.001; SIF760: R2 = 0.72, p < 0.001) for the subtropical evergreen coniferous forest without water stress. Drought interfered with the utilization of the improved backward approach because of the decoupling of SIF and GPP due to stomatal closure. This new approach offers new insight into the estimation of diurnal canopy SIF and can help understand the photosynthesis of vegetation for future climate change studies.

Highlights

Chlorophyll Fluorescence (ChlF) is regarded as a prospective marker of vegetation photosynthetic activity and a vital indicator of the carbon cycle
We proved that the backward approach improved with the correction factor k could capture the diurnal dynamics of canopy solar-induced chlorophyll fluorescence (SIF) under normal weather conditions
We explored the practical approaches for the estimation of diurnal SIF dynamics using measured and simulated data for a typical subtropical evergreen coniferous forest site in eastern China

Summary

Introduction

Chlorophyll Fluorescence (ChlF) is regarded as a prospective marker of vegetation photosynthetic activity and a vital indicator of the carbon cycle. Leaf chlorophyll molecules capture light energy and transmit it to the reaction centers to release through three pathways: Remote Sens. The physics-physiology mechanism linking the photosynthetic function to ChlF indicates that the fluorescence can be an observable and valid indicator of vegetation photosynthetic activity. With the recent advancements in remote sensing techniques, solar-induced chlorophyll fluorescence (SIF) can be detected by remote sensing instruments and has been found to be correlated with gross photosynthetic carbon dioxide (CO2 ) assimilation or gross primary production (GPP) at the canopy and landscape scales [3,4,5,6]. The application of fluorescence signals to derive plant photosynthesis for regional and global carbon cycle research has received increasing attention

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