Comparing and Contrasting Root and Leaf Properties of Tropical and Desert Agaves

Physiological and structural differences between tropical and desert agaves were investigated in four representative species. Two well studied species, A gave shawii and A. deserti , are native to arid environments in southern California, while A. colimana and A. dasyliroides are native to a seasonally moist tropical region in western Mexico. Over the course of six weeks, transpiration rates and stomatal conductance during regular watering, drought, and recovery were measured using a porometer. Measurements were taken during daylight and after dark to observe the periods of highest photosynthetic activity. To further investigate the relationship between photosynthesis and environment, stomatal impressions were taken to determine during which hours the stomata opened to allow for transpiration. The data collected by the porometer and stomatal impressions suggest that under well watered conditions A. dasyliroides employs C3 photosynthesis, with a tendency to shift towards CAM photosynthesis under more stressful conditions. These results contrast with the other species investigated where there was no significant difference between photosynthesis during the night and day. The presence of C3 photosynthesis in a primitive tropical species of agave can give insight into the photosynthetic evolution of agaves and the mechanisms behind the transition from the earlier (C3) to the more advanced (CAM) photosynthetic pathway in this genus