Vergara - 1976 - Physiological and morphological adaptability of ri

oativrrn awn NLTTI-UENI‘ UPFARE or RICE ncitirs 273
markedly than nutrient absorption by lowland rice; second. that the nutritional
disorders of rice plants at low‘ temperature are not successfully detected by leaf
0r shoot analysis alone.
The experiment carried out by Fujiwara and lshida (1963) falls into an iiitennediale
position between the two experiments of Takahashi. Yanagisawa.
Kono. Yazavi-‘a. and Yoshida (1954). They investigated the response of rice
placed under a low temperature condition of 17°C for 1 to 3 weeks at the stage
of active tillering. and shtiwed that the nutrient uptake was depressed more
considerably by prolonged duration of low temperature treatment. The dcprcs~
sion order nearly agreed with that found by Takahashi, Yanagisatva, Kono,
Yazawa. and Yoshida (1954) in their long-term experiment, except for phosphorus.
Fujiwara and lshida (il9(i3) found that the absorption of manganese was
greatly enhanced by low temperature. Subsequently re-examining the enhancement
of manganese uptake at low temperature by the use of soils of difrerent
manganese content. Ishida and Fujiwara (1965) concluded that the enhanced
uptake of manganese was not attributable to the content of available manganese
in soils but to the physiological changes caused by 10w temperatures in rice
plants. The discrepancy in manganese absorption at a low temperature bettveeti
Takahashi, Yanagisawa. Kono, Yazawa. and Yoshida (1954) and Fujiwara and
lshida (1963) might be explained by the difference in oxidation-reduction of
soils and in experimental duration, since the latter authors recognized that the
absorption of manganese sometimes dropped below the control if the redox
potential of soil was relatively high or the duration of low temperature treatment
was further extended.
Similar to the influence of temperature. the effect of light intensity on nutrient
uptake by rice roots depends greatly on the duration of treatment.
Yazawa (1960. unpublished) investigated the effect of different light intensities,
100, 50. 25. and 0% of natural sunlight. on nutrient uptake by rice plants at the
booting stage. In this study, the absorption experiments, each covering a 2.5-hr
period. were repeated successively five times from 0600 to 1850. The results.
as presented in Table 2. showed that the reduction in light intensity most considerably
depressed the uptake of ammonium-nitrogen and water. followed by
nitrate-nitrogen. potassium. silicon. and phosphorus. indicating a marked
difference from the effect of low temperature.
In another experiment. Yazatva (1962, unpublished) investigated the residual
effect of darkness on the nutrient uptake by rice plants. Lou-land rice grown in
culture solution was placed in the darkness for a day or a week at booting stage,
then transferred to natural sunlight; the nutrient uptake was measured after l_. 2,
and 4 day's. The results are shown in Table 3. Though the stronger effect of
darkness for a week than for a day is quite reliable. it is noticeable that the
remarkable ditference in the rate of recovery of nutrients developed after the
plant was exposed to sunlight. The capacity of roots to absorb water and silicon
recovered very quickly in natural sunlight. regaining more than 90% water and
silicon writhin 4 days. whereas the capacity to absorb ammonium-nitrogen,