Developmental light environment and net gas exchange of cocoyam (Xanthosoma sagittifolium).
X. sagittifolium cv. South Dade White was grown in the field in 100, 50 or 30% sunlight. Mean integrated photosynthetic photon fluxes (PPF) in unshaded treatments were 35.0 mol/m2 per d in 2 trials and 37.4 mol/m2 per d in 2 other trials. Net CO2 assimilation (A) and water use efficiency were highest in unshaded plants. Substomatal CO2 concentration increased with increased shading but stomatal conductance (gs) and transpiration were not significantly affected by treatment. Diurnal patterns for A were positively correlated with gs, lamina temperature, relative humidity and PPF. Lamina N concentrations, on lamina DW or lamina area bases, increased with increased PPF. Shaded plants had higher chlorophyll:N (DW basis) and lamina area:lamina DW ratios than unshaded plants, indicating increased photosynthate and N allocation to leaves in shaded plants and maximization of light interception.