Unraveling the physical and physiological basis for the solar- induced chlorophyll fluorescence and photosynthesis relationship using continuous leaf and canopy measurements of a corn crop

Peiqi Yang,Petya K E Campbell,Elizabeth M Middleton,Christiaan Van Der Tol

doi:10.5194/bg-18-441-2021

Abstract

Abstract. Estimates of the gross terrestrial carbon uptake exhibit large uncertainties. Sun-induced chlorophyll fluorescence (SIF) has an apparent near-linear relationship with gross primary production (GPP). This relationship will potentially facilitate the monitoring of photosynthesis from space. However, the exact mechanistic connection between SIF and GPP is still not clear. To explore the physical and physiological basis for their relationship, we used a unique data set comprising continuous field measurements of leaf and canopy fluorescence and photosynthesis of corn over a growing season. We found that, at canopy scale, the positive relationship between SIF and GPP was dominated by absorbed photosynthetically active radiation (APAR), which was equally affected by variations in incoming radiation and changes in canopy structure. After statistically controlling these underlying physical effects, the remaining correlation between far-red SIF and GPP due solely to the functional link between fluorescence and photosynthesis at the photochemical level was much weaker (ρ=0.30). Active leaf level fluorescence measurements revealed a moderate positive correlation between the efficiencies of fluorescence emission and photochemistry for sunlit leaves in well-illuminated conditions but a weak negative correlation in the low-light condition, which was negligible for shaded leaves. Differentiating sunlit and shaded leaves in the light use efficiency (LUE) models for SIF and GPP facilitates a better understanding of the SIF–GPP relationship at different environmental and canopy conditions. Leaf level fluorescence measurements also demonstrated that the sustained thermal dissipation efficiency dominated the seasonal energy partitioning, while the reversible heat dissipation dominated the diurnal leaf energy partitioning. These diurnal and seasonal variations in heat dissipation underlie, and are thus responsible for, the observed remote-sensing-based link between far-red SIF and GPP.

Highlights

For our understanding of the Earth’s climate, estimates of the gross carbon uptake by terrestrial ecosystems are crucial (Falkowski et al, 2000; Friedlingstein, 2015; Solomon et al, 2009)
The APARcanopy–gross primary production (GPP) relationship was apparently comprised of parallel groups of responses with a large variation in GPP exhibited for the same levels of APARcanopy (Fig. 1b)
This relationship complies with the common understanding of the response of photosynthesis to light, showing the well-known saturation with irradiance as photosynthesis of the whole canopy gradually shifts from light limitation to carbon limitation, while the unexplained variation in GPP can be attributed to stomatal aperture responses and a time-varying carboxylation capacity, especially in the upper sunlit canopy, which experienced larger variations in light intensity

Summary

Introduction

For our understanding of the Earth’s climate, estimates of the gross carbon uptake by terrestrial ecosystems are crucial (Falkowski et al, 2000; Friedlingstein, 2015; Solomon et al, 2009). Yang et al.: Unraveling the solar-induced chlorophyll fluorescence and photosynthesis relationship continuous and dense data, but these observations are only indirectly related to GPP In this respect, the development of Sun-induced chlorophyll fluorescence (SIF) measurement techniques from satellites has raised expectations. Ever since satellite SIF data products related to the far-red fluorescence peak became available during the past decade, numerous studies have reported a strong correlation between far-red SIF and GPP at the local, regional and global scales (e.g., Campbell et al, 2019; Damm et al, 2015; Guanter et al, 2014; He et al, 2017; Wieneke et al, 2016) This SIF– GPP link has been employed to estimate photosynthetic capacity (e.g., Zhang et al, 2014) and crop yield (e.g., Guan et al, 2016)

Methods

Results

Discussion

Conclusion