HIGH PHOTOSYNTHETIC CAPACITY IN A SHADE-TOLERANT CRASSULACEAN ACID METABOLISM PLANT - IMPLICATIONS FOR SUNFLECK USE, NONPHOTOCHEMICAL ENERGY-DISSIPATION, AND SUSCEPTIBILITY TO PHOTOINHIBITION

Aechmea magdalenae Andre ex Baker, a constitutive Crassulacean acid me tabolism (CAM) plant from the shaded Panamanian rain forest understory , has a maximum photosynthesis rate 2 to 3 times that of co-occurring C-3 species and a limited potential for photosynthetic acclimation to high light. Chlorophyll fluorescence measurements indicated that (a) c ompared with co-occurring C-3 species, photosynthetic electron transpo rt in A. magdalenae responded more rapidly to light flecks of moderate intensity, attained a higher steady-state rate, and maintained a lowe r reduction state of plastoquinone during light flecks; (b) these char acteristics were associated with phase III CO2 fixation of CAM; (c) wh en grown in full sun, A. magdalenae was chronically photoinhibited des pite a remarkably high nonphotochemical quenching capacity, indicating a large potential for photoprotection; and (d) the degree of photoinh ibition was inversely proportional to the length of phase III. Results from the light fleck studies suggest that understory A. magdalenae pl ants can make more efficient use of sun flecks for leaf carbon gain ov er most of the day than co-occurring C-3 species. The association betw een the duration of phase III and the degree of photoinhibition for A. magdalenae in high light is discussed in relation to the limited phot osynthetic plasticity in this species.