Whole-plant carbon dioxide exchange responses of Angelonia angustifolia totemperature and irradiance

Light and temperature responses of whole-plant CO2 exchange were determined for two cultivars of Angelonia angustifolia Benth., 'AngelMist Purple Stri pe' and 'AngelMist Deep Plum'. Whole crop net photosynthesis (P-net) of 'An gelMist Purple Stripe and 'AngelMist Deep Plum' were measured at eight temp eratures, ranging from 17 to 42 degreesC. P-net for both cultivars increase d from 17 to approximate to 20 degreesC, and then decreased as temperature increased further. Optimal temperatures for P-net of' AngelMist Purple Stri pe 'and' AngelMist Deep Plum' were 20.8 and 19.8 degreesC, respectively. Th ere was no significant difference between the two cultivars, irrespective o f temperature. The Q(10) (the relative increase with a 10 degreesC increase in temperature) for P-net of both cultivars decreased over the entire temp erature range. Dark respiration (R-dark) of both cultivars showed a similar linear increase as temperature increased. As photosynthetic photon flux (P PF) increased from 0 to 600 eta mol.m(-2).s(-1), P-net of both cultivars in creased. Light saturation was not yet reached at 600 mu mol.m(-2).s(-1). Th e light compensation point occurred at 69 mu mol.m(-2).s(-1) for 'AngelMist Purple Stripe' and at 89 mu mol.m(-2).s(-1) for 'AngelMist Deep Plum'. The lower light saturation point of 'AngelMist Purple Stripe' was the result o f a higher quantum yield (0.037 mol.mol(-1) for 'AngelMist Purple Stripe' a nd 0.026 mol.mol(-1) for 'AngelMist Deep Plum'). The difference in quantum yield between the two cultivars may explain the faster growth habit of 'Ang elMist Purple Stripe'.