Photosynthetic responses of cassava cultivars (Manihot esculenta Crantz) from different habitats to temperature

Maximum photosynthetic CO₂ exchange rates (P_n) of single attached leaves were determined for several cassava cultivars selected from different habitats and grown in pots outdoors at CIAT, Colombia, S.A. P_n rates were in a narrow range of 22 to 26 mol CO₂ m^–2s^–1 for all cultivars tested when measured at high photon flux density, normal air, optimum temperature and with low leaf-air vapor pressure differences. For all tested cultivars (9 cvs.), there was a broad optimum temperature for P_n between 25 to 35°C. At temperatures below and above this range P_n declined in all cultivars with P_n rates reaching 80% of maximum at 20 and 40°C. P_n temperature coefficient (Q₁₀) from 15–25°C was 1.6±0.2 across cultivars. No consistent relation existed between P_n, optimum temperature, and the original habitat.