Yoshida - 1981 - Fundamentals of Rice Crop Science

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198 FUNDAMENTALS OF RICE CROP SCIENCE change is expressed as (McCree 1974): dW/dt = D – N, (5.7) where D = daytime net total of CO 2 taken up by the plant and N = night total of CO 2 evolved by the plant. When dW/dt is expressed per unit of ground area (g dry matter/m 2 per day or week), it is called crop growth rate (CGR). The crop growth rate is used as a measure of primary productivity of crops in the field. 5.1.2. Characteristics of rice photosynthesis Rice is generally believed to have a C-3 photosynthetic pathway (Ishii et al 1977b). There is, however, a report that suggests the operation of both C-3 and C-4 pathways in a salt-tolerant indica variety (Hegde and Joshi 1974). As a C-3 plant, rice has a high CO 2 compensation point, exhibits photorespiration, and lacks bundle sheath chloroplasts (Table 5.2). Compared with other C-3 species, however, rice has a relatively higher net photosynthetic rate per unit of leaf area. Within Oryza sativa, indica rices have a higher optimum temperature than japonica rices. Early papers on rice photosynthesis reported a leaf photosynthetic rate of 10–20 mg CO 2 /dm 2 per hour, while recent papers indicate a rate of 40–50 mg CO 2 /dm 2 per hour. This difference could be attributed primarily to improvements in the measuring technique (Yoshida and Shioya 1976). In early studies on rice photosynthesis, the CO 2 exchange rate was measured by enclosing several cut leaves in aplastic chamber. Later studies, however, use an intact leaf. The photorespiration rate increases with increasing light intensity, but the rate of photorespiration relative to the rate of CO 2 fixation is higher at lower light intensities. At light intensities lower than 10 klx, photorespiration accounts for 70–90% of CO 2 fixation. At 40 klx, it accounts for 40% (Ishii et al 1977c). At the moment, lowering the oxygen concentration in air is the most convenient means of reducing photorespiration. A group of plant growth regulators can also reduce photorespiration and increase photosynthetic activity (Zelitch 1979). When rice was grown in a low-oxygen atmosphere, both photosynthesis and dry matter production increased; grain yield decreased due to an increased percentage of unfertile grains. The percentage spikelet fertility of Tangin Bozu and Hoyoku varieties decreased from 86 and 74% in the 21% O 2 atmosphere to 22 and 46% in the 3% O 2 atmosphere, respectively (Akita and Tanaka 1973). Thus, inhibiting photorespiration by lowering the oxygen concentration did not increase the grain yield. 5.1.3. Crop photosynthesis Crop photosynthesis in the field is primarily determined by incident solar radiation, photosynthetic rate per unit leaf area, leaf area index, and leaf orientation.
Photosynthetic characteristics Measured results Experimental conditions References Table 5.2. Some characteristics of rice photosynthesis. Light compensation point 400–1,000 Ix 25°C, 300 ppm CO 2 Murata (1961) lshii et al (1977c) Murata (1961) Murata (1961); lshii et al (1977a) Osada (1964) lshii et al (1977c) Akita et al (1968); Takano and Tsunoda (1971); Yoshida and Shioya (1976) lshii et al (1977b) Akita et al (1969) Akita and Miyasaka (1969); lshii et al (1977a, c) saturation Temperature optimum optimum Carbon compensation point dioxide Net photosynthetic rate Biochemical pathway Bundle sheath chloroplasts Photorespiration 45–60 KIx 20–33°C (for japonica) 25–35°C (for indica) 55 ppm 40–50 mg CO 2 /dm 2 per h C-3 pathway None Present 30°C, 300 ppm CO 2 300 ppm CO 2 , 50 klx 300 ppm CO 2 , 50 klx 25°C, > 10 klx optimum temperature, light saturation
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FOREWORD Rice is vital to more than
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CONTENTS Foreword Preface GROWTH AN
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3.2. Adaptation to Submerged Soils
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4.5. Corrective Measures for Nutrit
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1 .1. OUTLINE OF THE LIFE HISTORY T
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GROWTH AND DEVELOPMENT OF THE RICE
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Table 7.6. An example of high yield
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REFERENCES AGRICULTURAL POLICY STUD
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Yoshida - 1981 - Fundamentals of Rice Crop Science

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