Vergara - 1976 - Physiological and morphological adaptability of ri

14S
cumara mo RICE
lamp type was supplemented at the blue and the red end of the spectrum by
other lamps, and each combination of lights provided the sole source of light
for the plants. Under these conditions, although there were some differences
among the species tested in their vegetative growth responses to the different
lamp combinations, the overall conclusion was that each was providing adequate
and satisfactory light for plant growth and development.
The second set of results [Table 2B) illustrates how far a spectrum can be
varied from a balance approximating that of a midday solar spectrum. particularly
with respect to the red and blue regions. If there are significant shifts. as
occurred in the lighting treatments used here, there can be considerable consequential
changes in plant growth habit. The general nature of the changes is
in accord with those well documented for plants grown under restricted red or
blue wavelength light, although the effects of the variation of spectral balance
were reduced as the intensity was increased.
Intensity
Artificial light sources should also be capable of providing high-intensity light
and in particular provide this without substantially distorting the spectral
balance. Lamps presently available make this practicable, and tests from lamp
rigs providing 400 Wm-I PAR have been carried out. ln considering the use of
these. it should be noted that l4 hours of irradiance at 400 Wm-= PAR will
provide over twice the total irradiance received from midday summer light on a
clear day at latitude 30, although the peak irradiance is still slightly below that
which would occur for about 2 hours under natural midday", clear-sky midsummer
conditions.
Table 3 shows some growth responses to high- and medium-intensity light for
two plant species growing under near-optimum temperature conditions. Both
species show a slight decrease in shoot dry weight and a considerable (20—30%)
reduction in plant height and total leaf area under the high light-intensity treatment.
Plants were grown for 7-10 day-‘s in the treatments before measurements
began. That allowed time [or new growth under the conditions of the treatment
Table 3. Comparison of two species grown under high and medium intensity lightdaylength
12 hr.
P68
17.5f12.5C Shoot height (cm) 22.9 27.1 B5
10mb/2mb VPD Shoot weight {g} 2.8 29 96
Leaf area (em!) 408 522 ‘EB
Corn
275422.56 Shoot height (cm) 75.3 102.0 i4
‘l0mb/2mb VPD Shoot weight (g) 6.0 82 97
Leaf area (em) 1061 1276 83
(Data collected after ‘l5 (corn) and 22 days (pea) under experimental conditions)
s.“ “stir Ht
i t i 4~
400g wm= 170g wm--‘ Mlas
0/’