A correlation between photosynthetic temperature adaptation and seasonal phenology patterns in the shortgrass prairie.

The temperatures at which chlorophyll fluorescence yield is substantially increased and the temperatures at which the quantum yield for CO uptake is irreversibly inhibited were measured for three shortgrass prairie species. The experimental taxa include, a cool season species (Agropyron smithii), a warm season species (Bouteloua gracilis), and a species which grows throughout the cool and warm seasons (Carex stenophylla). Agropyron smithii exhibited lower high temperature damage thresholds (43°C in cool grown plants, 46°C in warm grown plants), relative to the other two species. Bouteloua gracilis exhibited the highest tolerance to high temperature, with threshold values being 44-49°C for cool grown plants and 53-55°C for warm grown plants. Carex stenophylla exhibited threshold values which were intermediate to the other two species (43-47°C for cool grown plants, and 51-53°C for warm grown plants). Seasonal patterns in the fluorescence rise temperatures of field grown plants indicated acclimation to increased temperatures in all three species. The results demonstrate a correlation between the high temperature thresholds for damage to the photosynthetic apparatus, and in situ seasonal phenology patterns for the three species.