Spectral properties and net photosynthesis of Aster tripolium L. and Halimione portulacoides (L.) Aellen leaves under saline and hypoxic conditions

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Abstract
Summary: Spectral properties of leaves of Aster tripolium L. and Halimione portulacoides (L.) Aellen grown under saline and hypoxic conditions were studied in relation to the net photosynthesis (Pn) of the leaves. Cuttings of A. tripolium and of H. portulacoides were grown in aerated or nitrogen flushed nutrient solution under glasshouse conditions. During a 13 d period both Pn and the directional spectral reflectance and transmittance of the adaxial surface of marked leaves was recorded. At the end of the experiment the water content and total chlorophyll content of the leaves was determined. The chlorophyll content and Pn of the leaves were highly correlated. Between 56 and 67 % of the variation in Pn could be accounted for by changes in chlorophyll content. Light absorption by the plant pigment was negatively correlated to the reflectivity. More than 91 % of the variation in reflectivity could be accounted for by changes in absorption. However, Pn of the two species grown under saline and hypoxic conditions was poorly or not correlated to spectral reflectance (r2= 0.07–0.14), and only 12–14% of the variation in absorptance could be accounted for by changes in Pn. The low correlation between Pn and spectral properties may be due to asymptotic spectral characteristics when chlorophyll content exceeded 2 mg g−1 d. wt and to changes in respiration and stomatal conductance that may influence Pn independent of reflectance.