ASSESSING PHOTOSYNTHETIC RADIATION-USE EFFICIENCY OF EMERGENT AQUATICVEGETATION FROM SPECTRAL REFLECTANCE

We studied the reflectance spectra of the emergent aquatic vegetation of Searsville Lake in coastal central California using a high spectral resolution hand-held spectroradiometer with the aim of assessing spec tral indices as indicators of photosynthetic radiation-use efficiency. The photochemical reflectance index (PRI), defined as (R-531 - R-570) /(R-531 + R-570), was strongly correlated with the ratio of secondary and protective pigments to chlorophyll a and with epoxidation state (E PS) of the xanthophyll cycle pigments (violaxanthin + 0.5 antheraxanth in)/(violaxanthin + antheraxanthin + zeaxanthin), and therefore, with photosynthetic radiation-use efficiency (PRUE) (measured as mol CO2 mo l(-1) photons). This reflectance-based measure seems to be useful as a remote index of aquatic vegetation photosynthetic function and physio logical status. These results extend and reinforce previous studies co nducted in terrestrial vegetation that indicate a functional relations hip between PRI, EPS, and PRUE at leaf and canopy scales. (C) 1997 Els evier Science B.V.