Vergara - 1976 - Physiological and morphological adaptability of ri

134 Curt-tan; AND RICE
solar elevation. However. the position of this level was consistently higher than
the level where the leaves were most densely displayed. Below this level. the CO1
absorption by sunlit leaves diminished considerably.
The heat-balance and aerodynamics] methods were used to evaluate the
value of CO, flux in the air above the rice crop (Yabuki et at. 1972; Ohtaki and
Seo. 1972. 1974; Seo and Ohtaki. 1974'. Uehijirna ct al. 197(1). Carbon dioxide
fluxes can be expressed as
P = Dt~2 (C1 _ C2) (26)
where P is the CO, flux. C , and C , are the CO1 concentration in the air at heights
z, and 2,. and D1,. is an exchange velocity between z, and 2,. The diurnal
variation of CO; flux evaluated from Eq. (26) gave reasonable results with a
maximum at midday where solar radiation was highest. Ishibashi (I970) measured
the upward llux of CO3 from underlying surfaces beneath the canopy and
A
4° 0......
m2’
30 2.2’
2O
0.65’
Q42
0.3
10 cm/sec
( gCOz-mi2day7) B
photosynthesis
Canopy
Net
3U
2O
00 3 6 8 12 l5 118
Solar radiation t MJ-m‘?day" )
18-
15-
l2—
9-
10 6 _
wu-m-ktay‘
Z7?‘
1
I
2
l
00 3
Exchange velocity , Dayna, ( cm/sec l
l0. A) Relationships between canopy photosynthesis
and radiation (Lfhijinla et a|._. 1974): B) Dependence of
canopy photosynthesis on air mixing (Llehiiima et a1-
I974).