Use of the Chlorophyll a/b Ratio as a Bioassay for the Light Environment of a Plant

Four bioassays for the light environment, obtained from three Veronica species, were critically compared for 20 field sites instantaneous electronic readings as a standard. Among total chlorophyll (leaf dry weight and leaf area basis), specific leaf area and the chlorophyll a to chlorophyll b ratio, the last provided the most realistic correlation, increasing with available light. The ratio is physiologically flexible, is least influenced by soil magnesium status or water availability, and is dissociated from patterns imposed by changes in leaf density