Utilization and dissipation of absorbed light energy in the epiphytic Crassulacean acid metabolism bromeliad Tillandsia ionantha

Past studies of the ability of epiphytic Crassulacean acid metabolism brome liads to acclimate to different light levels yield conflicting findings; so me indicate that these plants are similar to shade plants whereas others st ress their similarity to sun plants. This study investigates the ability of individuals of Tillandsia ionantha to acclimate to low or high irradiance. Plants were exposed to 100 and 800 mu mol m(-2) s(-1) photosynthetic photo n flux density under controlled conditions for 4 wk. Individuals exposed to the lower light level exhibited higher chlorophyll concentrations and high er photosynthetic rates at low light relative to plants exposed to high lig ht. Low-light plants also exhibited a greater efficiency in the photochemic al utilization of absorbed light energy and a lower ability to dissipate ex cess energy nonphotochemically, relative to the plants exposed to the highe r light level. Photosynthetic rates at high light were similar in both sets of plants, reflecting the higher efficiency of energy conversion in the lo w-light plants and an apparent saturation of photosynthetic capacity in the high-light plants. The latter may have resulted from high-light-induced da mage to the photosynthetic apparatus in addition to an increase in nonphoto chemical dissipation of excess light energy. The higher capacity for harmle ss dissipation of excess light energy in the high-light plants should prove beneficial in plants growing in exposed locations and subject to drought a nd nutrient stresses. Thus, the results support and expand those of previou s studies: T. ionantha can acclimate to both low and high light but does so in different ways. Such flexibility in adjusting the photosynthetic appara tus to varying light levels constitutes a valuable adaptation to growing th roughout the canopy of a host tree.