Vergara - 1976 - Physiological and morphological adaptability of ri

GROWTH AND smrranzm UPTAKE or RICE ROOTS 277
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DISCUSSION
A. TANAKA (Chairman): In discussing the ettbct of environmental factors on nutrient
absorption by roots, Dr. ‘Yoshida emphasized the importance of association between
the shoot and the roots: as the shoot and the roots are closely related morphologically
and physiologically, the interpretation of various phenomena should be made on this
basis. He also emphasized the differential etTects of a treatment depending upon the
duration 0t‘ treatment: a short-term treatment gives direct etTects on nutrient absorption
by the roots. whereas a long-term treatment gives complex effects on the photosynthetic
rate of the shoot. translocation of photosynthates from the shoot to the roots.
respiratory‘ rate of the roots, nutrient absorption. and cumulative effects of these
processes. Temperature or light have direct, cumulative, and residual etfeets on various
physiological processes. and temperature and light fluctuate in various fashions in
actual rice production. Thus, a set of climatic factors at a certain growth stage of a
crop in actual fields will have quite ditlerent significance to the nutrient absorption
during the whole growth cycle of the crop. Considering these complexities. our kBIJW-l
edge at present is far from complete.
Available information on the effect ol‘ environmental conditions on nutrient absorption
reviewed by Dr. Yoshida is mostly qualitative rather than quantitative, because
the relationships is very complicated. and also the efforts made so far along this line
have not been so intensive as on other physiological processes such as photosynthesis
or respiration. Although it is fundamental rather than practical. more eflbrts should be
made to understand the mechanism of nutrient absorption by the roots. especially in
relation to the unique environmental conditions of the roots of lowland rice (submerged
condition).
He pointed out the necessity to study the adaptability and tolerance of the roots to
unfavorable climatic conditions in relation to growth. activity of aerial parts. and
grain yield. 1 agree with his view. One of the reasons why we lack such information
is that we did not have precise devices to control the temperature of the roots and
the shoot, separately and simultaneously. For this purpose phytotrons will contribute
enormously.