Vergara - 1976 - Physiological and morphological adaptability of ri

268 ciriyrprna AND RICE
the oxytgen supply of rice plants (Alberda. 1953). In their first and subsequent
studies on the distribution of roots in different layers of paddy soils. Kawata et
al. (1963. 1969) found that the roots which emerged from upper and lower shoot
units were mainly distributed in the upper layer of furrow soil. and that the
number of deeply penetrating roots in subsoil beneath the rice plant was proportional
to the depth of plowsole and the rate of water percolation.
Concerned with the distribution of riee roots in paddy soils. Tei (1933) gave
evidence that more than a half of the total roots were distributed in the shallow
layer of the soil. with an extending angle of more than 54°. Salo (1937) observed
that about two thirds of the roots were distributed in the upper 20 centimeters
of paddy soil while only l to 2 percent of the roots penetrated to soil exceeding
50 centimeters in depth. The investigations by Kavrata ct al. (1963. 1969) are
important in that they show that the root distribution of lowland rice in paddy
soil can be characterired by the shoot unit and by the upper and lower roots of
a unit.
On the other hand, most ecological studies on rice roots have been rnadc to
determine the relation of roots to the characters of aerial parts that affect yield.
Iu-‘atsuki (1932). Tei (1933). and Salo (1937) attempted to relate measurements of
rice roots to the characters of shoots, but the correlations they obtained. despite
their ascertions, were not always cleareut. Recently Lee and Ota (1973), using
the theory of Fujii, investigated in detail the relationship between morphological
and physiological characters of nodal roots and of shoots, and its effect on rice
yield. They proved that the number of spikelets per panicle was closely related
to the diameter of the third to sixth nodal roots. particularly at the third leafshoot
unit from the top. The erectness and chlorophyll content of the flag leaf.
together with the number ofliving leaves at the milk ripening stage. showed high
positive correlation with the m-naphthylamine oxidizing power of the roots at
the three uppermost rotit-initiating nodes.
The physiological significance of periodical and synchronized emergence and
elongation of leaves and roots to the growth of lowland rice was confirmed by
nutrio-phyrsitwlogical studies. For example. Tanal-za (I958). feeding the leaves at
different positions on the main stem with "CO, at the young panicle initiation
stage. investigated the metabolism of radioactive photosytnthetic products and
found evidence that the lower leaves were related to roots. whereas the upper
ones were closely connected xyith the young panicle, indicating the division of
ivork among the leaves at different positions. lle explained those facts by applying
the concept of the “chain-structure unit" (lshizuka and Tanaka. 1963)
which resembles the shoot unit proposed by Kawata et al. (1967) (see Fig. 2).
Ueda and Mitsui (1967) found periodical variation in nutrient uptake by rice
seedlings grown in culture solution in response to leaf emergence.
Thus. the growth of a root and development of its functions show" an intimate
connection with those of the aerial parts in both morphological and physiological
aspects. Therefore, consideration should be given to these aspects
when the effects of environmental factors on rice roots are studied.