Photosynthetic characteristics of a tropical forest understory herb, Alocasia macrorrhiza, and a related crop species, Colocasia esculenta grown in contrasting light environments.

Photosynthetic acclimation to 5 light environments ranging from 2 to 60% full sun was determined in Alocasia macrorrhiza, a shade tolerant species from tropical forest understories, and Colocasia esculenta, a cultivated species which occurs naturally in open marshy areas. Photosynthetic capacities of both species increased nearly 3 fold with increased photon flux density (PFD). In a given environment, however, photosynthetic capacities of C. esculenta were double those of A. macrorrhiza. Stomatal limitations explained only a small part of this difference. Respiration rates and estimated biochemical capacities increased in parallel to photosynthetic capacity. No differences were observed either between species or environments in the ratio of RuBP regeneration capacity to carboxylation capacity as determined from the CO2 dependence response of photosynthesis. Quantum yields of both species decreased only slightly with increasing growth PFD, providing little evidence for photoinhibition at high PFD. The results are discussed in terms of the mechanisms of and limitations on acclimation in these two species.