Photosynthetic Response of Flooded Rice (<i>Oryza sativa</i>) and Three<i>Echinochloa</i>Species to Changes in Environmental Factors

Abstract

The photosynthetic responses of rice (C 3 ) and three Echinochloa species (C 4 ), barnyardgrass, early watergrass, and late watergrass, to changes in CO 2 intercellular partial pressure, light intensity, and leaf temperature were investigated under laboratory conditions. The three Echinochloa species exhibited photosynthetic responses characteristic of C 4 plants. The three weedy species showed higher efficiency for CO 2 utilization at low CO 2 intercellular partial pressure (CO 2 i) than rice. Compensation and saturation of CO 2 i for photosynthesis were lower in the weedy species than in rice. The maximum photosynthetic rates at high light intensity were 33.5, 32.7, 30.5, and 21.5 μmol CO 2 m -2 s -1 for barnyardgrass, early watergrass, late watergrass, and rice, respectively. Photosynthesis temperature optimum was 35 to 37 C for the three Echinochloa species and 33 C for rice. Overall, under simulated summer conditions, the four taxa showed a photosynthetic ability hierarchy with regard to gas exchange performance as follows: barnyardgrass ≥ early watergrass &gt; late watergrass &gt; rice.