Chlorophyll fluorescence, photochemical reflective index and normalized difference vegetative index during plant senescence
The relationship between the Photochemical Reflectance Index [PRI], Normalized Difference VegetationIndex [NDVI] and chlorophyll fluorescence along senescence was investigated in this work. Reflectanceand radiance measurements were performed at canopy level in grass species presenting different pho-tosynthetic metabolism: Avena sativa [C3] and Setaria italica [C4], at different stages of the naturalsenescence process. Sun induced-chlorophyll fluorescence at 760 nm [SIF760] and the apparent fluo-rescence yield [SIF760/a, with a = irradiance at time of measurement] were extracted from the radiancespectra of canopies using the Fraunhofer Line Discrimination-method. The photosynthetic parametersderived from Kautsky kinetics and pigment content were also calculated at leaf level Whilst stand level NDVI patterns were related to changes in the structure of canopies and not inpigment content, stand level PRI patterns suggested changes both in terms of canopy and of pigmentcontent in leaves. Both SIF760/a and PSII decreased progressively along senescence in both species. Astrong increment in NPQ was evident in A. sativa while in S. italica NPQ values were lower. Our mostimportant finding was that two chlorophyll fluorescence signals, PSIIand SIF760/a, correlated with thecanopy PRI values in the two grasses assessed, even when tissues at different ontogenic stages werepresent. Even though significant changes occurred in the Total Chlr/Car ratio along senescence in bothstudied species, significant correlations between PRI and chlorophyll fluorescence signals might indicatethe usefulness of this reflectance index as a proxy of photosynthetic RUE, at least under the conditions ofthis study. The relationships between stand level PRI and the fluorescence estimators [PSIIand SIF760/a].
PHOTOCHEMICAL REFLECTANCE INDEX NORMALIZED DIFFERENCE VEGETAION INDEX SUN INDUCED CHLOROPHYLL FLUORESCENCE RADIATION USE EFFICIENCY PHOTOSYNTHEC PARAMETERS SENESCENCE