CONICET | Buscador de Institutos y Recursos Humanos

Senescence is a key process in plants controlled by onthogeny but also by environmental factors. A reduction in chlorophyll concentration and in photosynthetic activity characerize senescence. The consequence of senescence of different functional aspects is critical to understant the influence of diverse stress factors. In this study senescence was evaluated in two grasses (Setaria italica a C4 species and Avena sativa C3 species) by non-destructive methods: reflectance spectroscopy and chlorophyll fluorescence to evaluate changes in pigments, on radiation use efficiency (RUE) and interception. Measures were performed at leaf and canopy levels. Both species were seeded and grown in pots. Radiance and reflectance spectra were recorded with a portable spectroradiometer FieldSpec Pro FR ASD equipped with leaf-clip accessories. From them, two spectral indices: PRI (a measure of RUE) and NDVI (a measure of photosynthetic active radiation absorption) were calculated. Fraunhofer Line Discrimination method was used to extract the sun induced fluorescence (SIF) from the small canopy in the telluric O2-A absorption line (760 nm). Photochemical parameters (Fv/Fm, effective quantum yield of PSII, qP, qNP, QNP) were obtained with a modulated fluorometer Hansatech. Measurements were performed on non-detached leaves. Pigments contents were also determined [1]. Parallel to the decrease in total chlorophyll content an increase in carotenoid/total chlorophyll ratio (Car/Chlor) was observed. The leaf PRI values decreased over time for both studied species. Canopy level values were more sensitive. NDVI values were less responsive. Canopy SIF (760 nm) decreased in time. We found that canopy level PRI correlated linearly and directly with SIF, Fv/Fm and effective quantum yield of PSII for Avena sativa, Setaria italica and both species combined; while inversely related with qNP, QNP and Car/Chlor.