Photosynthetic Response of Flooded Rice (Oryza sativa) and ThreeEchinochloaSpecies to Changes in Environmental Factors

Abstract

The photosynthetic responses of rice (C3) and threeEchinochloaspecies (C4), barnyardgrass, early watergrass, and late watergrass, to changes in CO2intercellular partial pressure, light intensity, and leaf temperature were investigated under laboratory conditions. The threeEchinochloaspecies exhibited photosynthetic responses characteristic of C4plants. The three weedy species showed higher efficiency for CO2utilization at low CO2intercellular partial pressure (CO2i) than rice. Compensation and saturation of CO2i 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 CO2m-2s-1for barnyardgrass, early watergrass, late watergrass, and rice, respectively. Photosynthesis temperature optimum was 35 to 37 C for the threeEchinochloaspecies 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 > late watergrass > rice.