Mechanistic evidence for tracking the seasonality of photosynthesis with solar-induced fluorescence

Abstract

Northern hemisphere evergreen forests assimilate a significant fraction of global atmospheric CO2 but monitoring large-scale changes in gross primary production (GPP) in these systems is challenging. Recent advances in remote sensing allow the detection of solar-induced chlorophyll fluorescence (SIF) emission from vegetation, which has been empirically linked to GPP at large spatial scales. This is particularly important in evergreen forests, where traditional remote-sensing techniques and terrestrial biosphere models fail to reproduce the seasonality of GPP. Here, we examined the mechanistic relationship between SIF retrieved from a canopy spectrometer system and GPP at a winter-dormant conifer forest, which has little seasonal variation in canopy structure, needle chlorophyll content, and absorbed light. Both SIF and GPP track each other in a consistent, dynamic fashion in response to environmental conditions. SIF and GPP are well correlated (R2 = 0.62–0.92) with an invariant slope over hourly to weekly timescales. Large seasonal variations in SIF yield capture changes in photoprotective pigments and photosystem II operating efficiency associated with winter acclimation, highlighting its unique ability to precisely track the seasonality of photosynthesis. Our results underscore the potential of new satellite-based SIF products (TROPOMI, OCO-2) as proxies for the timing and magnitude of GPP in evergreen forests at an unprecedented spatiotemporal resolution.

Varying Contributions of Drivers to the Relationship Between Canopy Photosynthesis and Far‐Red Sun‐Induced Fluorescence for Two Maize Sites at Different Temporal Scales

“…The contributions of PAR in , fPAR, LUE, and F 760,y to the variations in GPP and F 760 might differ at early growth stages as well as at the seasonal scale across the whole growing season. In addition, the rapid change of canopy structure and physiology of crop ecosystems differs from many natural ecosystems like forests or grasslands (Magney et al, ). Further studies are required to test whether the findings and the framework in this study are applicable or not to a different period of the growing season for maize or to other ecosystems with different characteristics of canopy structure and physiology.…”

Cropland Carbon Uptake Delayed and Reduced by 2019 Midwest Floods

“…SIF has been shown to be a robust proxy for GPP (Frankenberg & Berry, ; van der Tol et al, ). While nonlinear relationships between GPP and SIF have been observed at leaf and flux‐tower scales under certain conditions, for example, strong incoming light (Magney et al, ; Verma et al, ), linear relationships have been generally observed at ecosystem and regional scales (Frankenberg et al, ; Li et al, ; Magney et al, ; Sun et al, ). The robust linear relationship at increasing scales is likely because satellite measurements are primarily measuring an integrated canopy average of low Photosynthetically Active Radiation (PAR).…”

Constraining estimates of terrestrial carbon uptake: new opportunities using long‐term satellite observations and data assimilation

“…Because SIF is a measurement of re‐emitted light, it is less prone to signal saturation in dense canopies (Frankenberg & Berry, ), and thus has the potential to provide improved coverage of tropical forest ecosystems. More recent satellite efforts to measure SIF, including NASA OCO‐2 and ESA TROPOMI, show high fidelity compared to ground observations (Köhler et al ., ; Magney et al ., ), providing increased confidence in the use of satellite SIF to accurately measure the timing and magnitude of GPP across diverse global ecosystems. The potential for satellite SIF observations as a constraint on CFE depends on continued development of merged, long‐term SIF records with well‐characterized estimates of uncertainty (Sun et al ., ; Schimel et al ., ); and improved logic for direct incorporation of SIF observations into models (Lee et al ., ; MacBean et al ., ; Norton et al ., ; Gu et al ., ; Schimel et al ., ).…”

“…Long-term satellite SIF observations are a direct measure of the light re-emitted from Chl during the light reactions of photosynthesis, and theory and observations show that SIF is correlated with photosynthetic activity in a dynamic fashion that is directly linked to APAR and LUE (Porcar-Castell et al, 2014;Yang et al, 2015;Smith et al, 2018;Magney et al, 2019) (Figs 2, 3). Thus, together satellite fAPAR and SIF estimates capture changes in photosynthesis per unit light absorbed (i.e.…”