Evidence suggests that many high-latitude evergreen ecosystems have increased in productivity in recent years in conjunction with increasing temperature ( 3– 5). Northern hemisphere evergreen forests represent a substantial fraction of the global carbon pool ( 1) and contribute significantly to the fluxes of CO 2 between the biosphere and the atmosphere ( 2). 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. 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. ![]() SIF and GPP are well correlated ( R 2 = 0.62–0.92) with an invariant slope over hourly to weekly timescales. Both SIF and GPP track each other in a consistent, dynamic fashion in response to environmental conditions. 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. This is particularly important in evergreen forests, where traditional remote-sensing techniques and terrestrial biosphere models fail to reproduce the seasonality of GPP. 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. ![]() ![]() Northern hemisphere evergreen forests assimilate a significant fraction of global atmospheric CO 2 but monitoring large-scale changes in gross primary production (GPP) in these systems is challenging.
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