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 metabolism (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) compared with co-occurring C-3 species, photosynthetic electron transport in A. magdalenae responded more rapidly to light flecks of moderate intensity, attained a higher steady-state rate, and maintained a lower reduction state of plastoquinone during light flecks; (b) these characteristics were associated with phase III CO2 fixation of CAM; (c) when grown in full sun, A. magdalenae was chronically photoinhibited despite a remarkably high nonphotochemical quenching capacity, indicating a large potential for photoprotection; and (d) the degree of photoinhibition was inversely proportional to the length of phase III. Results from the light fleck studies suggest that understory A. magdalenae plants can make more efficient use of sun flecks for leaf carbon gain over most of the day than co-occurring C-3 species. The association between the duration of phase III and the degree of photoinhibition for A. magdalenae in high light is discussed in relation to the limited photosynthetic plasticity in this species.