Conference Agenda

Understanding the maximum photosynthetic capacity of terrestrial plants is central to the FLEX mission because this key variable mediates the relationship between the environmental drivers of photosynthesis, the rate of gross carbon dioxide fixation, and the emission of chlorophyll fluorescence. Recent advances in experimental studies have led to the development of an invertible leaf-level model of photosynthesis that resolves two of the proteins that are key determinants of maximum photosynthetic capacity: the Cytochrome b6f complex, which controls the activity of the electron transport system, and Rubisco, which controls the activity of carbon metabolism (DOI: 10.1007/s11120-021-00840-4). In this presentation, I will discuss progress implementing this leaf-level photosynthesis model within different styles of land surface modeling frameworks, and strategies for performing inversions that are driven by fluorescence observations to retrieve estimates of maximum photosynthetic capacity. I will also discuss upcoming opportunities for collaboration to calibrate and validate FLEX-derived estimates of maximum photosynthetic capacity using in situ measurements of the photosynthetic proteins across key plant functional types. Finally, I will discuss how these activities lay the groundwork for future development of a novel FLEX data product that quantifies leaf Cytochrome b6f and Rubisco contents in a way that is complementary to the already planned products for leaf chlorophyll and carotenoid contents, and some examples of potential applications to understanding the large-scale responses of terrestrial vegetation to global environmental change.

The effects of climate warming in the Arctic are two-to-four times more prominent than at lower latitudes, thus extending the growing season and possibly increasing the vegetation productivity. Consequently, an increase in emissions of Biogenic Volatile Organic Compounds (BVOCs) is expected. BVOCs can be emitted by vegetation for different purposes, including pollinator attraction, defense, plant-to-plant communication, and as a response to biotic and abiotic stress. Specific groups of BVOC are emitted with a clear ecological function, whilst others have an uncertain purpose. Generally, the total BVOCs emissions are regulated by biomass, temperature, soil moisture and received radiation.

Isoprenoids, a group of BVOCs, are known to be driven by photosynthetic processes. For example, isoprene is synthesized during photosynthesis and protects plants against e.g. heat and oxidative stress. Our hypothesis is then that the emissions of selected BVOCs groups (in particular isoprenoids) can be linked to remotely sensed proxies of photosynthetic activity.

In this study, we propose to explore the link between Solar-Induced chlorophyll Fluorescence (SIF) in the O₂-A absorption band and BVOCs emission rates in a field spectroscopy framework (using a FOX-2 spectrometer, JB Hyperspectral Devices GmbH), so to further investigate the relationship between the reflectance properties of vegetation and emitted BVOC rates. The vegetation under examination are typical species found in low Arctic tundra: Empetrum nigrum, Betula nana, Vaccinium uliginosum, and Carex bigelowii. The concurring measurements of BVOCs emissions and spectroscopy took place in the area of Kobbefjord, Greenland, during the summer of 2024.

The performed analysis included steps of wavelength selection, feature ranking importance and construction of Structural Equation Models to verify the links between the remotely sensed variables (spectral and photosynthetic indices) and the emission rates of various BVOCs groups.

The results show that the most important wavelengths for the emissions of BVOCs are found in proximity to the O₂-A and O₂-B absorption bands for several BVOCs groups. The feature importance rankings show that SIF is moderately important for the emissions of isoprene and total BVOCs, while the most important abiotic drivers are canopy/soil temperature and PAR. Interestingly, other spectral/photosynthetic indices such as EVI, PRI and MTCI appear at the top of the ranking for monoterpenes, sesquiterpenes, and isoprene respectively. The importance of SIF for the emissions of isoprene and total BVOCs is corroborated by the built Structural Equation Models.

These findings can potentially be of aid in opening new avenues to model BVOCs emissions at larger scale, as SIF and other relevant indices can be directly derived with UAV and satellite imagery.

.