Assessing photosynthetic radiation-use efficiency of emergent aquatic vegetation 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 spectral indices as indicators of photosynthetic radiation-use efficiency. The photochemical reflectance index (PRI), defined as (R331 - R570)/(R531 + R570), was strongly correlated with the ratio of secondary and protective pigments to chlorophyll a and with epoxidation state (EPS) of the xanthophyll cycle pigments (violaxanthin + 0.5 antheraxanthin)/(violaxanthin + antheraxanthin + zeaxanthin), and therefore, with photosynthetic radiation-use efficiency (PRUE) (measured as mol CO2 mol-1 photons). This reflectance-based measure seems to be useful as a remote index of aquatic vegetation photosynthetic function and physiological status. These results extend and reinforce previous studies conducted in terrestrial vegetation that indicate a functional relationship between PRI, EPS, and PRUE at leaf and canopy scales.