Agriculture Reference
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regimes. Irrespective of growth temperature the maximal
rates of photosynthetic assimilation rate was found to be at
30-35°C in rice. However, photosynthetic assimilation rate
measured at the growth temperature remained almost constant
irrespective of temperature. Biomass production and relative
growth rate was greatest in rice grown at 30°C/24°C. The
net assimilation rate in rice decreased at low temperature
(19°C/16°C) though there is no much differences in leaf area
ratio. The nitrogen use effi ciency (NUE) for growth rate (GR)
estimated by dividing net assimilation rate (NAR) by nitrogen
content correlated with GR and with biomass production
(Nagai and Makino 2009).
In a tiller, the photosynthetic rate of leaves at different node
positions was infl uenced by temperature and nitrogen level.
At low temperature (22°C/17°C). There was no signifi cant
difference of photosynthesis among leaves at different node
positions under different nitrogen treatments. However, when
plants grew at higher temperatures lower photosynthetic
rate was found at lower positioned leaves under low level of
nitrogen, but not under higher level of nitrogen. There was
higher nitrogen content (both soluble protein and total amino
nitrogen) in plants grown at lower temperature as compared
with those of higher temperature. Leaf nitrogen content is
usually positively correlated with leaf photosynthetic rate.
The enzyme activities (RuBPCase) and cytochrome c oxidase
were low under all nitrogen treatments of plants grown at low
temperature (Shieh and Liao 1987) (Fig. 20).
When a cold-tolerant cultivar Xiangnuo 1 and a cold
sensitive cultivar IR50 was exposed to chilling for 2 days,
the photosynthetic rates declined dramatically by 48.7% and
67.5% respectively in seedlings. Chlorophyll fluorescence
measurement indicated that the reaction centres and antenna
