The Influence of Stress Conditions on Chlorophyll Content of Two Range Grasses with Contrasting Photosynthetic Pathways

The influence of various treatments and temperature regimes on total chlorophylls and on the chlorophyll a:b ratio of western wheatgrass and blue grama plants was investigated at different time intervals during the 120-day growth period. Western wheatgrass, a C₃ species, accumulated greater amounts of chlorophyll than did blue grama plants, a C₄ species. Maximum concentrations (mg gd · wt⁻¹) of chlorophylls in western wheatgrass and in blue grama were recorded at the lower (13/7 °C) and higher (30/18 °C) temperature regimes. Nitrogen fertilizer alone decreased the chlorophyll content in both species. The chlorophyll a:b ratio in blue grama ranged from an average of 2·00 under irrigated plus fertilized conditions to 3·00 under control and fertilized conditions. On the other hand, the chlorophyll a:b ratio in western wheatgrass remained constant at 3·00 throughout the growing season under various treatments and temperature regimes.