AFTERNOON INHIBITION OF PHOTOSYNTHESIS IN MAIZE .2. ENVIRONMENTAL CAUSES AND PHYSIOLOGICAL SYMPTOMS

Environmental causes of the afternoon inhibition of photosynthesis that is frequently observed under field conditions in maize (Zea mays L.) leaves were investigated by exposing plants to various photosynthetic photon flux density (Q), temperature, and air saturation-deficit (Δe) environments during the day. Results obtained by manipulating the environment of potted plants grown outdoors were compared with the responses to day-to-day variation in environment in field-grown plants. Afternoon inhibition of photosynthesis only occurred if whole shoots were exposed to both high Q and high Δe. This suggested that plant water-deficits rather than feedback inhibition or photoinhibition were responsible. Leaf water-potentials were lower when photosynthesis was reduced. During the afternoon inhibition of photosynthesis, apparent quantum yield was not reduced, and stomatal closure did not occur. Photosynthetic rates at limiting substomatal pressures of carbon dioxide were much lower during afternoon inhibition of photosynthesis. © 1990.