Detecting mangrove photosynthesis with solar-induced chlorophyll fluorescence

Accurately understanding the photosynthesis of mangroves is essential for inferring how climate change influences the terrestrial and marine carbon cycle. However, photosynthesis of mangroves remains poorly understood due to the difficulty of in situ flux data acquisition. Remote sensing of solar-induced chlorophyll fluorescence (SIF) provides a direct proxy for photosynthesis which would be an effective tool for detecting mangrove photosynthesis. We presented the first SIF observations from both ground and unmanned aerial vehicle (UAV) platforms in a mangrove forest and provided an exploratory attempt to downscale SIF from canopy level to leaf level to better characterize photosynthesis. We found that relationships between mangrove photosynthesis and SIF vary by light condition, which exhibited a negative correlation under low-light condition but positive correlation under high-light condition. Moreover, we found that inter-species differences affect the relationship between photosynthesis and SIF in mangroves. Relationship exhibited more clear-cut correlation by distinguishing mangrove species than considering them as a whole. Our results would help to better understand the photosynthesis mechanism of the mangrove forests and fills the gap of the relationship between SIF and photosynthesis in subtropical and tropical wetland ecosystems.