SAMBA – Solar-induced chlorophyll fluorescence (SIF) in the AMazon BAsin

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Gross Primary Production (GPP) through photosynthesis is the single largest uptake mechanism of atmospheric CO2 and thus drives the variability of the airborne fraction of anthropogenic CO2 emissions. A significant amount of carbon is cycled through tropical rainforests, globally accounting for about 34% of CO2 uptake by photosynthesis, or GPP. However, GPP in tropical rainforests remains poorly understood due to large biases of traditional measurement methods. To address this critical knowledge gap, the project ‚SAMBA – Solarinduced chlorophyll fluorescence (SIF) in the Amazon Basin‘ aims to quantify the carbon uptake and photosynthesis of tropical rainforests and to analyze how they are linked to environmental conditions. We propose to make use of a new observation method to detect solarinduced chlorophyll fluorescence (SIF), which is an indicator for photosynthetic activity and provides an estimation of GPP. During photosynthesis, parts of the solar radiation absorbed by chlorophyll are re-emitted at longer wavelengths (650 – 850 nm) after absorption of photosynthetically active radiation (PAR), so-called SIF with two emission peaks in the red (~685 nm) and the far-red (~740 nm) spectral region. However, canopy observations, which are needed to link in-situ leaf data with remotely-sensed global scale data of SIF, are sparse. The proposed work will build on the applicant‘s experiences using the recently developed next- generation canopy SIF instrument - PhotoSpec - to perform spatially resolved simultaneous red and far-red SIF and vegetation index observations. A PhotoSpec instrument will be build based on the original PhotoSpec design developed at UCLA between 2015 and 2018, including modifications adjusted for tropical rainforests deployments. The instrument will be deployed in the Amazon rainforest of Brasil for data collection to obtain continuous estimates of SIF and ecosystem GPP. We propose to exploit this comprehensive data set with an existing set of carbon cycle observations and soil-canopy models to investigate changes in seasonal phenology, CO2 fluxes, and ultimately the fate of atmospheric CO2 from tropical rainforests. Data from the activities will improve the process-based knowledge on SIF and gross CO2 fluxes that is urgently needed to better constrain model simulations of photosynthetic processes and carbon fluxes. These activities will advance fundamental research at the intersection of atmospheric, biological and environmental sciences, and provide critical information to evaluate the predicted feedbacks of climate change.