Yoshida - 1981 - Fundamentals of Rice Crop Science

PHOTOSYNTHESIS AND RESPIRATION 197
Table 5.1. Comparison between the C-3 and C-4 plants in photosynthetic performance.
C-3 plants C-4 plants Reference
1. Optimum temperature
for photosynthesis
2. Optimum light intensity
for photosynthesis
3. Photosynthetic rate
per unit leaf area
4. Maximum growth
rates under
optimal condition
5. Water use efficiency
15–30°C 30–45°C Hatch (1973)
30–50% full Full sunlight Hatch (1973)
sunlight
C-4 is about 2 times higher Hatch (1973)
than C-3 under optimal conditions
34–39 g/m 2 50–54 g/m 2 Monteith (1978)
per day
per day
1.49 mg dry 3.14 mg dry wt/ Downes (1969)
wt/g water g water
group from ATP to form PEP, thus regenerating the initial CO 2 acceptor molecule.
The over-all efficiency of using CO 2 increased by this additional cycle.
Rice belongs to the C-3 plants. The C-3 pathway operates in most temperate
cereal crops such as wheat and barley. Plants adapted to warm climates use the C-4
pathway: sugarcane, maize, sorghum, and millet, and also several important
pasture species. The C-4 plants have several advantages for crop production
(Table 5.1). The characteristics of the C-4 pathway suggest that the C-4 plants are
well adapted to a climate with high temperatures, high light intensity, and limited
water supply during the period of active growth.
When photosynthesis occurs, dark respiration is assumed to take place simultaneously.
Hence, measured photosynthesis is the difference between true photosynthesis
and dark respiration. On the basis of this concept, gross photosynthesis
refers to the sum of net (measured) photosynthesis and dark respiration:
Gross photosynthesis = net photosynthesis + dark respiration.
Recently, the discovery of photorespiration has caused confusion in the above
concept. However, the term net photosynthesis can be used safely because it is the
measured net gain in photosynthesis; both dark respiration and photorespiration
have been subtracted.
Photorespiration, a characteristic of C-3 plants, has been the subject of intensive
research in recent years (Jackson and Volk 1970, Tolbert 1971, Zelitch 197 1,
1979). Photorespiration does not produce any ATP and does not provide any
useful carbon skeletons for the biosynthesis of new compounds or new tissues.
Photorespiration occurs in peroxisomes, whereas dark respiration takes place in
mitochondria. Hence, photorespiration is totally different from dark respiration.
For these reasons, the classical term gross photosynthesis is still useful when
growth is considered.
Net photosynthesis is normally measured by CO 2 intake or by O 2 output. Dry
weight increases are also often used as estimates of net photosynthesis after
appropriate corrections are made for mineral content. The rate of dry weight