PHOTOFLUX · Global assessment of plant photosynthesis optimization for climate change versus enhanced plant productivity

Millions of years of evolution have produced extraordinary adaptations and solutions for plants to face the naturally excessive solar energy which commonly cannot be fully utilized by the light harvesting pigments of leaves. To find a balance between the harvesting of and the protection against the solar radiation conditions, all plants employ flexible thermal or non-photochemical energy dissipation mechanisms. Yet, inherent capacities for these flexible dissipation mechanisms differ between plant species and can change along seasonal conditions but also short-term physiological strain of the plants. The optimized balance between the photochemical and non-photochemical energy pathways of absorbed radiation is a very dynamic concept which remains physically poorly understood. Deriving these energy components and assessing them in a global context would greatly advance our knowledge on the basic energy functioning of vegetation, making room for possible improvements in food production or understand required capacities to cope with climatic changes. With the ambition to quantify actual photosynthesis from space for agricultural management units, ESA will launch in 2024 the FLuorescence Explorer (FLEX) as 8th Earth Explorer mission equipped with a novel sensor payload dedicated to the retrieval of solar-induced fluorescence and the reflectance at a high-spectral resolution. This proposal, named PHOTOFLUX, will take a novel approach to spectrally disentangle the photochemical and non-photochemical components of harvested light, building on a quantitative understanding of the energy partitioning within the light reactions. Not only will this strategy serve a bottom-up conceptual understanding of the photosynthetic light harvesting at global scale, it will also bring the possibilities to quantitatively assess productivity under the climatic constraints and the need to dissipate the excess energy to keep photosynthesis at optimal rates.