Integrating Solar Induced Fluorescence and the Photochemical Reflectance Index for Estimating Gross Primary Production in a Cornfield

William Kustas,Elizabeth Middleton,Craig Daughtry,Yen-Ben Cheng,Qingyuan Zhang,Bruce Cook,Lawrence Corp,Karl Huemmrich,Petya Campbell

doi:10.3390/rs5126857

Abstract

The utilization of remotely sensed observations for light use efficiency (LUE) and tower-based gross primary production (GPP) estimates was studied in a USDA cornfield. Nadir hyperspectral reflectance measurements were acquired at canopy level during a collaborative field campaign conducted in four growing seasons. The Photochemical Reflectance Index (PRI) and solar induced chlorophyll fluorescence (SIF), were derived. SIF retrievals were accomplished in the two telluric atmospheric oxygen absorption features centered at 688 nm (O2-B) and 760 nm (O2-A). The PRI and SIF were examined in conjunction with GPP and LUE determined by flux tower-based measurements. All of these fluxes, environmental variables, and the PRI and SIF exhibited diurnal as well as day-to-day dynamics across the four growing seasons. Consistent with previous studies, the PRI was shown to be related to LUE (r2 = 0.54 with a logarithm fit), but the relationship varied each year. By combining the PRI and SIF in a linear regression model, stronger performances for GPP estimation were obtained. The strongest relationship (r2 = 0.80, RMSE = 0.186 mg CO2/m2/s) was achieved when using the PRI and SIF retrievals at 688 nm. Cross-validation approaches were utilized to demonstrate the robustness and consistency of the performance. This study highlights a GPP retrieval method based entirely on hyperspectral remote sensing observations.

Highlights

Carbon sequestration by terrestrial ecosystems is a key factor underpinning a comprehensive understanding of the carbon budget at a global scale
Clear seasonal dynamics were observed for gross primary production (GPP), which increased during the green-up vegetative stage, reached the highest productivity during mid-season, and steadily declined after that (Figure 1a)
We examined the capability of the Photochemical Reflectance Index (PRI) and solar induced chlorophyll fluorescence (SIF) to track plant photosynthetic function in order to estimate diurnal variations of GPP in a cornfield over multiple growing seasons

Summary

Introduction

Carbon sequestration by terrestrial ecosystems is a key factor underpinning a comprehensive understanding of the carbon budget at a global scale. Terrestrial plants fix carbon through photosynthesis, known as gross primary production (GPP) at the ecosystem scale—the largest carbon exchange between the biosphere and the atmosphere [1]. Remote sensing observations provide a unique opportunity to track photosynthetic activities at various spatial and temporal scales, and much effort has been put towards this goal over the past decades. Many remote-sensing-based indices and algorithms were developed and utilized to track leaf biochemical properties (e.g., chlorophyll, water content) and canopy biophysical properties (e.g., leaf area index, LAI; absorbed photosynthetically active radiation, APAR; fraction of APAR, fAPAR) have been applied to the estimation of GPP in various ecosystems, with variable success [2,4,5,6,7,8,9,10,11,12,13,14].

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