Effect of Pretreatment Temperature on Response of Photosynthesis Rate in Maize to Current Temperature.

Abstract

Maize plants (hybrid XL45) were exposed to three temperature treatments of different duration: a 'growth' temperature (extending from sowing to the day before photosynthetic measurements were made), an 'acclimation' temperature (exposure to a given temperature for 24 h) and a 'measurement' temperature (the temperature during the photosynthetic measurement, 30-45 min duration). The measurement temperature had the greatest single effect on photosynthetic rate, which increased 2-3-fold between 16 and 35°C. The highest rate of apparent photosynthesis was measured in plants grown at 25°C, acclimated at 35°C and measured at 35°C (2.1 mg m-² s-¹). The relative contribution of stomatal and residual resistances to the total resistance to CO2 uptake changed little with temperature treatment, but the absolute magnitude of these resistances was strongly affected by temperature. Stomatal resistances ranged from 200 to 700 s m-¹. The stomatal resistance dominated, accounting for 65-80% of the total resistance to apparent photosynthesis. Chlorophyll concentrations changed in response to both growth and acclimation temperatures. Those grown at 16°C had the lowest concentration, those grown at 35°C the highest. The chlorophyll concentration changed over a 24-h acclimation period in both expanding and fully expanded leaves, increasing when plants were transferred to higher temperature and decreasing when the transfer was to lower temperature.