Satellite solar-induced chlorophyll fluorescence and near-infrared reflectance capture complementary aspects of dryland vegetation productivity dynamics

Mounting evidence indicates dryland ecosystems play an important role in driving the interannual variability and trend of terrestrial carbon sink. Nevertheless, our understanding seasonal dynamics ecosystem uptake through photosynthesis [gross primary productivity (GPP)] remains relatively limited due part to availability long-term data unique challenges associated with satellite remote sensing across ecosystems. Here, we comprehensively evaluated longstanding emerging vegetation proxies their ability capture GPP dynamics. Specifically, evaluated: 1) reflectance-based normalized difference index (NDVI), soil adjusted (SAVI), near infrared reflectance (NIRv), kernel NDVI (kNDVI) from MODerate resolution Imaging Spectroradiometer (MODIS); 2) newly available physiologically-based proxy solar-induced chlorophyll fluorescence (SIF) TROPOspheric Monitoring Instrument (TROPOMI). As a performance benchmark, used estimates robust network 21 western United States eddy covariance tower sites that span representative gradients climate functional composition. We found NIRv SIF were best performing captured complementary aspects types. offered better than other low-productivity, sparsely non-evergreen vegetated (R2 = 0.59 ± 0.13); whereas high-productivity sites, including evergreen-dominated 0.74 0.07). Notably, grass-dominated all (NDVI, SAVI, kNDVI) showed significant bias (hysteresis) strengthened total fraction woody cover, likely patterns are unrelated or decoupled GPP. Future efforts fully integrate strengths could significantly improve representation satellite-based models.