Effects of high temperature upon photosynthesis, respiration, and growth and yield of rice plants : a controlled environment study

Abstract

Effects of high temperature upon photosynthesis, respiration, and growth and yield of rice plants (Oryza sativa L.) were studied under controlled environments. Photosynthesis and respiration were determined by the CO2 exchange using the infrared gas analysis technique. Growth and development were evaluated by measuring agronomic characteristics and leaf stage, respectively. The yield performance was estimated by measuring yield characteristics. Short term high temperature in the vegetative stage did not affect yield characteristics. Variations of agronomic characteristics and development patterns occurred for short period of time after treatments, suggesting that growing points and some metabolic activities may be injured rather than the carbon balance. High temperature in the grain -filling stage affected yield through lower spikelet numbers, high percentage of sterility and reduced grain weights. Diurnal changes of stomatal conductance were observed under controlled environments. A decreasing trend of stomatal conductance was found in the vegetative growth phase. Conductance increased dramatically from panicle initiation through heading to early grain -filling, which may be a compromise of its own carbon economy. Stomatal movements of rice plants were sensitive to temperature changes. High temperature stimulated the opening of stomata yet preserved diurnal pattern of stomatal variations. High temperature enhanced the CO2 exchange rates in both stages. Temperature effects on the carbon balance were through the changes of the relationship between growth and maintenance. Differences in the daily gain of carbon between treatments depended on the counterbalance of synthetic rate versus respiration rate. The yield of growth was little affected by temperature yet increased slightly from young plant to matured plant, suggesting changes in the com position of biosynthetic end products. High temperature increased maintenance coefficient (m) because metabolic rate increased with increasing temperature. The value form decreased from the vegetative stage to the grain -filling stage, suggesting changes of the protein fraction and composition. Substrates consumed in respiration were utilized more in maintenance than in growth. High temperature enlarged the respiration differences. Obviously, less biomass was produced from the available substrates consumed in heat-treated plants of a greater demand for maintaining the existing plant biomass.