Vergara - 1976 - Physiological and morphological adaptability of ri

Pl-FfSItTS OF CONTROLLED ENVIRONMENT AND PLANT (IYROWTH 153
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DISCUSSION
NlONTETI-I (Chairman): I think it is instructive to consider Dr. k-litchells discussion of phytotron
physics in the light of Dr. Llchijimas paper on lield physics.
Uchijima was concerned with the geometry of radiative transfer in crop stands. Mitchell
refers to the desirability of "an even diffuse flux over the plant-gowing area“ which is certainly
not representative of the sun or even over the hemispherical source of light provided by an overcastshy.
Llehijima discussed the nature of turbulence in crop stands. whereas Mitchell simply quotes
an airflow of 0.3 to 0.5 m-"s in his own installation.
Llchijima drew our attention to the vertical distribution of temperature in a paddy field.
Mitchell presented his results in terms of air temperatures. assumed more or less uniform
throughout the growing Space.
Now despite the fact that the environment of plants in phytotrons differs from the field environment
in these and other important ways. we know it is pusible to grow plants which look
remarkably like plants of the same species growing in the field. (Lloyd Evans makes this comparison
quantitative and convincing in his paper.) The implication is that the spatial distribution
of radiation cannot be of paramount importance provided it is reasonably‘ uniform; that
temperature gradients are unlikely to be significant unless they are exceptionally large; and that
air movement is unlikely to be a determinant of growth rate provided the air from is fast enough
to prevent large deficits of CO; from developing in the space which plants occupy.
However, there is one point where it will always be extremely ditficult to simulate the natural