The main conclusions of many investigations about general requirements of plants for spectral composition of PAR (photosynthetically active radiation) are based on phylogenetic aspects of plant growth. We think that these aspects are not the main criteria in choosing the spectral composition required for growing plants in controlled conditions. Our approach to this problem is based on plant and crop reaction under long duration growth with specific spectra and intensity. Only in this way can we determine correctly the role of light characteristics for developing crops

Tikhomirov, Alexander A.

English

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SPECTRAL COMPOSITION OF LIGHT AND
GROWING OF PLANTS IN CONTROLLED ENVIRONMENTS
Alexander A. Tikhomirov
<± "
N96- 18126
Institute of Biophysics, Krasnoyarsk, 660036, Russia
The main conclusions of many investigations about general requirements of plants for spectral
composition of PAR are based on phylogenetic aspects of plant growth (Kleshnin et al., 1980; Geiger,
1994; et al). We think that these aspects are not the main criteria in choosing the spectral composition
required for growing plants in controlled conditions. Our approach to this problem is based on plant and
crop reaction under long duration growth with specific spectra and intensity. Only in this way can we
determine correctly the role of light characteristics for developing crops.
Why does it happen? In this connection it will be useful to examine the curve of the action spectrum of
photosynthesis. This classical curve is formed under controlled influence of light that involves av 3-5
minutes irradiation with one specific spectral flux. The form of this curve is similar for green leaves of
different species of plants. We've obtained different curves for spectral affectivity of green leaf
photosynthesis (on the example of radish), when plants have had long duration adaptation (for some
days) to lamps of different spectral composition and PAR intensity (Fig. 1, curves 1 and 2). The spectral
of these lamps is shown in the Short Note by Prikupets and Tikhomirov in this publication. We feel the
obtained differences have the following reasons. During short time intervals, only reactions of quick
photoregulation are possible. These reactions affect only functional characteristics of the photosynthetic
leaf system. In that time, structural changes do not occur and these i'eactions to light aren't observed.
The classical action spectrum of photosynthesis (Fig. 1, solid line) shows the universal characteristics of
green leaves of different plant species. Plants have the same types of green pigments (chlorophyll),
photosystems, reaction centers, pathways of energy migration to reaction centers and so on (Tikhomirov
et al., 1987; 1991).
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az r,.)
t12
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1,0-
0,5-
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! I ! I J I
400 500 600 700
Wavelength (rim)
25
Fig. l. The relative spectral
efficiency of photosynthesis of green
leaves of radish plants grown for 15
days under different PAR spectral
lighting. Photosynthetic
measurements for 400-500 mm were
taken with plants grown under blue-
light lamps, for 500-600nm under
green light lamps, for 600-700nm
under red-light lamps. 1) radiation
intensity during growth of plants was
50 W m 2 PAR (radiation intensity for
unsaturated photosynthesis). 2)
radiation intensity growth of plants
was 200 W m 2 PAR (radiation
intensity for saturated photosynthesis)
('gikhomirov et al.. 1987;1991). Solid
line is average value of relative
spectral photosynthetic efficiency of
green leaves according to McCree
(1972), Inada (1976, 1977).
https://ntrs.nasa.gov/search.jsp?R=19960011690 2020-06-16T05:53:52+00:00Z
Therefore, usage of the curve for action spectrum of photosynthesis is not correct in light regulation
under long-term stationary regimes, since certain reactions to spectrum and intensity of PAR aren't tal.:en
into consideration. All spectral requirements obtained under short light influence tests have similar
limitations.
What should be done? It's necessary to be guided by data obtained under long-term influence of spectral
and intensity characteristics on photosynthetic plant systems and even better on canopies of plants.
These are the photosynthetic structures which ultimately form to produce the harvested yield. We've
obtained some results which support this conclusion. These are some of the universal responses
(Tikhomirov et al., 1991):
1) The time for maximum affectivity of photosynthesis of plant canopies appears earlier
with red (600-700 nm) and later may shift to shorter wave length regions of PAR. This shift
depends on specific plant reaction to spectrum of PAR;
2) The relative effectiveness of blue rays increases and green and red rays decreases with higher
levels of irradiation (Fig. 2 and 3);
3) Maximum photosynthesis of canopies is possible only under combinations of blue, green and
red radiation. Any kind of combinations of two of these wavebands or with only one spectral
region, always reduces productivity.
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Fig. 2. The relative spectral efficiency of photosynthesis of cucumber leaves adapted to long
duration growth with radiation of different energy and spectral composition. B = 400 - 500nm,
G = 500 - 600nm, R = 600 - 700nm. a) 12 W m -2 (Ko, 1974): b) 24 W m -2 (Ko, 1982); c) 50 W
m '_ (Tikhimirov et al., 1991 ); d) 100 W m -2 (Tikhomirov et al., 1991 ).
26
o.)
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¢..)
r"
0
_0_
20-
_0 m
0
B
i i I I I l
100 200 300 400 500 600
Irradiance (W m a)
Fig. 3. The photosynthetic rate of
15d-old radish canopies with
irradiance of differing spectral
composition and intensities (B = 400-
500nm, G = 500-600nm, R = 600-
700nm). (Tikhomirov, et al., 1991).
It is not necessary to provide light conditions for maximum photosynthesis of every plant leaf but to
provide light conditions for optimal photosynthesis of the plant canopy. As a general rule over long
periods, photosynthesis systems grow old very quickly. The effect of leaf age on photosynthic rate is
shown in Figure 4 using cucumbers.
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...a
(1)
a_
c-
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e-.
o,8- B
I I I
2'0 ' '40 60
Time (d)
Fig. 4. The photosynthetic rate of cucumber per
canopy area for PAR irradiances of 100 W m 2
with 400-500nm (B), 500-600nm (G), or 600-
700nm (R) during canopy development
(Tikhimirov et al., 1991).
Optimal photosynthesis of plant leaves involves a harmonious relationship between spectrum and the
intensity of PAR. Thus, plants "work" to obtain the maximum photosynthetic efficiency (but the
photosynthesis is not maximum for each leaf) (Tooming, 1984).
There is a question. Is it necessary to prepare optimal light conditions for the photosynthesis of all
leaves on the plant or not? What way is it determined? The correct'decision on spectral composition of
light depends very much on certain morphological characteristics of plants. There is a dependance upon
the distribution of fruits along a stem (Tikhomirov, 1990). For example, cucumber has equal
distribution of fruits along the stem. There every leaf supplies assimilate to its fruit. In this connection
cucumber leaves at all layers must be provided with optimal light conditions. This requires a large
portion of green rays in PAR (about 40%). Red rays in PAR (about 40%) provide high level of
photosynthesis of upper leaves. Green rays penetrate into middle and lower leaves of plants. Blue rays
have regulatory function, but its part in PAR is not very big (about 20%) (Tikhomirov, 1989).
We have another situation, where fruits of a plant concentrate in the upper part of the stem. Classical
example is wheat. The car of wheat is supplied with assimilates, primarily from the upper leaves. With
this crop, PAR must have approximately 60-70% red rays (Tikhomirov, 1090). We've obtained data on
27
specificreactionsof plantsfor thespectralcompositionof PAR. It's particularlyimportantduringphmt
developmentprocesses.Accordingto thispoint of view plantsmaybedividedinto two groups(Tikhomirovet al., 1991):
1) Thefirst groupis characterizedwith restrictedgrowthanddevelopmentprocessesat
definiteontogeneticphasesif thePAR spectrumandintensityarenot optimized(i.e.,
cucumber,sunflower);
2) Thesecondgroupincludeplantscapableof passingthroughall ontogeneticSphases and
producingaharvestirrespectiveof thePARspectrumandintensityprovided(for example:
tomatoes,wheat).
Wheatis capableof passingthroughall phasesof ontogenesisregardlessof anyspecificspectral
irradiation. It's correctfor PARrangeof 100-600W m2 andpossiblyevenhigher. Tomatoeshavemore
restrictedPARrangein comparisonwith wheat. With a PARof 200Wm2 andhigher,tomato
productivity is loweredin redrays. PARrangefor radishappearedto bemorenarrow. Evenwhenred
andgreenlight isequalat aPARof 200 Wm2,plantsof radishperish. Cucumbersappearedto bethe
mostgreatlyinfluencedbythespectrumof PAR. Forexamplein redwavelengthswith lessthanPARof
50Wm2, plantsdie.
Weshouldn'tignorethesegreatdifferencesin reactionof plantsonspectrumandPAR intensity. All
compromisingdecisionsincludingintroductionof universalspectrumof irradiationleadto partial lossof
productivity.
Equal-energeticspectrum("white" light) or aspectrumsimilarto curveof theactionspectrumof
photosynthesishavebeenproposedfor useasauniversalspectrafor plantsgrowingunderlamplighting.
Thefirst might bechosenbecauseof considerationof phylogenesisof plants,thesecond- becauseof
researchfamiliar to you (McCree,1972;Inada,1976).Eitherof theseoptionscouldbeacceptedasa
temporarycompromisefor initial research.
I donotbelievethatwehaveto copy illuminationof plantsin naturalconditionsfor usein controlled
environmentgrowing. For examplethere'snoneedto growsomespeciesof plantsunderalternative
light darkperiods. Ourresearchshowedthatproductivityof someplants(radish,wheat)canbe
increasedundercontinuousirradiation(Tikhomirovet al., 1976;Lisovskyet al., 1987). Also, we
shouldnotstrictly aspireto duplicatingmorphophysiologicalcharacteristicsof field grownplants. Thus,
for example, we achieved a very large radish productivity when we sharply changed its
photomorphogenesis (Tikhomirov et al., 1976). This is true for increasing cucumber productivity too.
However, if we accept this concept, we must know where and how we should deviate from natural
conditions to increase productivity of plants grown in controlled environments. So I have the following
suggestions:
1) As a temporary measure the draft guideline distributed by the organizing committee might be
recommended for usage for plants grown in controlled environments;
2) Research work should be expanded to identify the spectrum of PAR radiation for each plan1
species which provides the maximum crop value.
If these suggestions are taken into consideration, my colleagues from Russia and I are ready to discuss a
program of research and take part in its conduct.
28
REFERENCES
Geiger,D. 1994. Spectralcompositionof light andgrowingof plantsin controlledenvironments.
(ReportatpresentWorkshop.)
Inada,K. 1976. Action spectrafor photosynthesisin higherplants. Plant and Cell Physiology, 17:355-
365.
Kleshnin A.F. Moskow, 1954. A plant and light. (In Russian) Moscow Academy of Science, Moscow,
USSR.
Lisovsky G.M., Sid-ko F.Y., Polonsky V.I., Tikhomirov A.A., ZoLOtukhin I.G. 1987. Light intensity
and quality as factors determining plant stand formation and yield under controlled artificial
illumination. Russian Plant Physiology. 34:636-643.
McCree K.J., The action spectrum, absorbance and quantum yield of photosynthesis in crop plants.
Agric. Meteorology 9:191-216.
Tikhomirov A.A. 1990. Spectral efficiency of productivity process and photometric aspects of light
culture of plants. (Doctoral dissertation in Biophysics). Krasnoyarsk, Institute of Biophysics.
Tikhomirov A.A. 1989. Photosynthesis of cucumber plants formed during radiation of different
spectral composition of PAR. Ukrainian Journal Physiology and Biochemistry of Plants. 21:3-8.
Tikhomirov A.A., Lisovsky G.M., Sid-ko F.I. 1991. Spectral composition of light and plant
productivity (In Russian). Nauka, Novosigirsk, USSR
Tikhomirov A.A., Zolotukhin I.G., Sid'ko F.Y. 1976. The influence of light conditions on the
productivity of quality of radish crop. Russian Plant Physiology. 23:502-507.
Tikhomirov A.A., Zolotukhin I.G., Lisovsky G.M., Sid'ko F.Y. 1988. Specific responses in various
plant species to the spectral composition of Photosynthetically active radiation under artificial
illumination. Russian Plant Physiology. 34:774-785.
Tooming X.G., 1984. Ecological principles of maximal productivity. (In Russian) Gidrometedizdat,
Leningrad, USSR.
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Spectral composition of light and growing of plants in controlled environments

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