Dry matter production and photosynthetic capacity in Gossypium hirsutum L. under conditions of slightly suboptimum leaf temperatures and high levels of irradiance.

Gossypium hirsutum L. var. Delta Pine 61 was cultivated in controlled-environment chambers at 1000-1100 μmol photosynthetically active photons m-2 s-1 (medium photon flux density) and at 1800-2000 μmol photons m-2 s-1 (high photon flux density), respectively. Air temperatures ranged from 20° to 34°C during 12-h light periods, whereas during dark periods temperature was 25° C in all experiments. As the leaf temperature decreased from about 33° to 27° C, marked reductions in dry matter production, leaf chlorophyll content and photosynthetic capacity occurred in plants growing under high light conditions, to values far below those in plants growing at 27° C and medium photon flux densities. The results show that slightly suboptimum temperatures, well above the so-called chilling range (0-12° C), greatly reduce dry matter production in cotton when combined with high photon flux densities equivalent to full sunlight.