PHOTOCHEMICAL REFLECTANCE INDEX AND LEAF PHOTOSYNTHETIC RADIATION-USE-EFFICIENCY ASSESSMENT IN MEDITERRANEAN TREES

This Letter presents new data validating the use of the photochemical reflectance index PRI (R570-R531)/(R570+R531) to assess photosynthetic -radiation-use-efficiency under mild water stress. Gas exchange, fluor escence and the PRI of leaves from the Mediterranean trees Quercus ile x and Phillyrea latifolia growing in the field were followed from spri ng to summer 1996 in central Catalonia (NE Spain). The same variables were measured in seedlings of these two species and Pistacia lentiscus submitted to progressive drying after witholding irrigation. Except f or severely drought damaged plants, significant relations of the refle ctance index PRI with fluorescence yield of the photosystem II (Delta F/F'(m)), nonphotochemical fluorescence quenching (qN) and photosynthe tic radiation use efficiency (PRUE) were found, thus indicating a func tional relation among these parameters. A simple portable radiometer m easuring ground level reflectance at narrow bands centred at 531 and 5 70 nm could instantaneously calculate the PRI index and give the PRUE estimation.