Vergara - 1976 - Physiological and morphological adaptability of ri

GROWTH into NUTRIENT urrrruoa OF RICE ROOTS 271
hydrogen sulfide. In this respect the investigation of Ueki (1960) is noteworthy
He observed severe browning 0r blackening of roots in rice plants grown at
37°C soil temperature. at which the number of roots was the largest. Furthermore.
the study of Yamada et al. (1954) concerning the effect of light showed
that the oxygen supply from aerial parts t0 roots through the conducting channel
in the rice plant was enhanced by increased photosynthetic activity in green
parts. Inada (1967) found a decrease in ascorbic acid OXldRSC and an increase in
peroxidase activity" in roots of rice grown under shading. In neither study is
there a reference to the effect on growth of roots.
EFFECT OF LIGHT INTENSITY AND TEMPERATURE ON
NUTRIENT UPTAKE OF ROOTS OF LOWLAND RICE
Both the requirement for mineral nutrients and the mineral content of rice
vary tvith the growth of the plant (lshizuka and Tanaka, 1952; Takahashi,
Murayama, Oshima, Yoshino, Yanagisawa, Keno, and Tsukahara 1954). As
predicted from the theory of growth unit already mentioned, marked similarity
was found in the seasonal change in the contents or mineral nutrients in roctts
and shoot, (Yoshida and Takahashi. 1958; Inada, 1967). The differentiation of
functions, or the division of work, in nutrient absorption developed between
new and old roots in response to their age; that is. new roots participated mostlf;
in water intake and old ones in nutrient uptake (Okajima, 1960). Nitrogen,
phosphorus. and potassium were actively‘ absorbed by young roots while iron,
manganese, sulfur, silicon, and magnesium tyere absorbed by mature ones
offlnada, 1967).
Consequently‘. the etfects of light intensity and temperature on nutrient uptake
by rice roots are not alivay-‘s the same; they vary’ with plant age and duration
of treatment or both.
An example of a short-term experiment on the effect of temperature on
nutrient uptake by rice roots was that performed by Takahashi, Yanagisawa.
Keno, Yazawa, and Yoshida (1954). Comparing the nutrient uptake by rice
seedlings at 30° and 16°C. they revealed that the absorption oftvatcr and mineral
nutrients was depressed by low temperature in the order phosphate > water
> ammonium > sulfate > potassium > magnesium > calcium (Fig. 3). This
resembles the lowering order in the experiment on inhibition of nutrient uptake
by hydrogen sulfide carried out by Mitsui et al. (1951), suggesting that the
reduction in nutrient absorption caused by low temperature was due to depressed
metabolism in rice roots.
Takahashi. Yanagizawa. Kono. Yazaw-"a, and Yoshida (1954) investigated
the effect of low temperature on the growth. yield. and nutrient absorption of
rice in a long-tenn experiment parallel to the experiment mentioned above. The
conditions employed in the experiment were more moderate than those in the
short-terrn one. Lowland rice plants were grown under cold water irrigation to
cool soil temperature by 3 to 5°C throughout the growing period. The results