Acebron, Kelvin: Combining Fluorescence and Reflectance to Quantify Dynamics in Photosynthetic Regulation. - Bonn, 2021. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
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author = {{Kelvin Acebron}},
title = {Combining Fluorescence and Reflectance to Quantify Dynamics in Photosynthetic Regulation},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2021,
month = dec,

note = {Photosynthesis in the field is anything but steady-state. Because environment is changing, understanding plant’s photosynthetic activity in situ is challenging. Measurement of solar-induced fluorescence (SIF), along with plant spectral reflectance (ρ), provides novel opportunity to understand the dynamic regulation of photosynthesis in the field. However, the interpretation of SIF is complicated by the photochemical and non-photochemical energy use in plant leaves. This thesis was aimed to establish a theoretical framework to link SIF and ρ with the photochemical and non-photochemical quenching (NPQ) of chlorophyll fluorescence (ChlF) at leaf level in order to elucidate the photosynthetic regulation in field conditions. First, I investigated the photosynthetic response of Chl-deficient soybean mutant during dark-to-light transition. Second, I traced SIF and ρ on a young canopy of turf grass after the application of Dicuran herbicide. Third, I probed the effect of different NPQ mechanisms on SIF and ρ using Arabidopsis thaliana having mutation on NPQ components that resulted to reduced NPQ capacity. Finally, I compared the photosynthetic response of glasshouse- and field-grown cassava plants in outdoor condition using active ChlF technique, passive SIF and ρ. As a result, Chl-deficient soybean mutant had lower NPQ, lower apparent Fyield, higher internal Fyieldf), lower fraction of open reaction centre (qL) and lower electron transport rate (ETR) as compared to wild type. While, no difference in PSII efficiency (ΦPSII) was observed. Meanwhile, SIF and photochemical reflectance index (PRI) significantly increased when photosynthesis was blocked using Dicuran herbicide, indicating a degree of sensitivity of both SIF and PRI to the build up in lumenal pH. Furthermore, the results in Arabidopsis npq mutants showed that decrease in NPQ had similar increase in SIF regardless of the impaired NPQ mechanisms. Analysis of diurnal ρ strongly suggests that diurnal change in ρ during summer is related to the activity of the xanthophyll cycle and not the PsbS-mediated conformational changes. When plants were suddenly exposed to cold, the onset of photoinhibition strongly quenched SIF in all Arabidopsis lines. Overall, the results I showed here covers the strength and limitations of remote sensing signals to quantify dynamic regulation in leaf photosynthesis and NPQ in the field and its contribution to the canopy productivity. In the future, parallel SIF and ρ measurements can be potentially used to test hypothesis on the functional role of NPQ in photosynthetic carbon gain in plants.},
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