FLUORESCENCE AND REFLECTANCE CHARACTERISTICS OF MANGANESE DEFICIENT SOYBEAN LEAVES - EFFECTS OF LEAF AGE AND CHOICE OF LEAFLET

Leaf reflectance and fluorescence characteristics of soybean (Glycine max cv 'Bragg') are influenced strongly by Mn availability. This report evaluates the effects of leaflet choice, leaf age, and leaf nodal position on several spectral characteristics. Leaves were obtained from soybeans grown hydroponically under controlled environmental conditions with wide differences in Mn supply. The ratio of 'constant yield' fluorescence (F-O) to 'variable yield' fluorescence (F-V), the ratios of reflectance at 750 nm to 550 nm and that at 650 nm to 550 nm, the position of the ''red edge'' near 700 nm, and an index of leaf ''yellowness'' were measured periodically. Increasing leaf age caused increases in the ''red edge'' and in both reflectance ratios. Leaf ''yellowness'' and the fluorescence ratio F-O/F-Y decreased with leaf age and increased with leaf nodal position, primarily in Mn deficient leaves. Effects arising from leaf choice were smaller than those caused by Mn deficiency.