Atmospheric CO2 Observations Reveal Strong Correlation Between Regional Net Biospheric Carbon Uptake and Solar-Induced Chlorophyll Fluorescence

Y.P. Shiga, J.M. Tadić, X. Qiu, V. Yadav, A.E. Andrews, J.A. Berry and A.M. Michalak


Remotely sensed solar-induced fluorescence (SIF), an emission from plant chlorophyll, offers the potential to track photosynthesis from space with unprecedented resolution and coverage. To date, analysis of SIF has been limited to either plot (~1 km2) or global/hemispheric scales, while regional scales (e.g., 1° × 1°, biome-level), those critical for policy decisions and informing carbon-climate feedbacks, remain unexplored. Using the dense North American network of atmospheric CO2 observations, we find that SIF outperforms existing vegetation indicators in tracking net CO2 exchange by exhibiting regional patterns more consistent with the atmospheric data. Furthermore, SIF informs a redistribution of the North American land sink via increased CO2 uptake in croplands and decreased CO2 uptake in needleleaf forests. These results highlight the potential of SIF to inform space-time patterns of the CO2 land sink at crucial regional scales.

Figure: Including SIF information leads to a redistribution of the growing season uptake from needleleaf forests to croplands (a). The difference between June, July, and August flux estimates obtained from inverse models with and without SIF (each using the three explanatory variables from Figure 1a) averaged over 3 years (2008–2010), with green (brown) indicating a stronger (weaker) uptake in the NEE estimates from the inversion including SIF. A biome map with atmospheric observation locations shown as circles with crosses is shown in Figure 2b. Biome outlines are shown as black lines (a). For unit conversion: 100 gC/m2 yr = 0.264 μmol/m2 s.


Recent studies have shown the promise of remotely sensed solar-induced chlorophyll fluorescence (SIF) in informing terrestrial carbon exchange, but analyses have been limited to either plot level (~1 km2) or hemispheric/global (~108 km2) scales due to the lack of a direct measure of carbon exchange at intermediate scales. Here we use a network of atmospheric CO2 observations over North America to explore the value of SIF for informing net ecosystem exchange (NEE) at regional scales. We find that SIF explains space-time NEE patterns at regional (~100 km2) scales better than a variety of other vegetation and climate indicators. We further show that incorporating SIF into an atmospheric inversion leads to a spatial redistribution of NEE estimates over North America, with more uptake attributed to agricultural regions and less to needleleaf forests. Our results highlight the synergy of ground-based and spaceborne carbon cycle observations.

Shiga, Y.P., J.M. Tadić, X. Qiu, V. Yadav, A.E. Andrews, J.A. Berry, A.M. Michalak (2018) "Atmospheric CO2 observations reveal strong correlation between regional net biospheric carbon uptake and solar-induced chlorophyll fluorescence," Geophysical Research Letters, 45 (2), 1122-1132, doi:10.1002/2017GL076630.