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selection the success o f any breeding procedure depends on
chance.
Literature Cited
1. Adams, M.W. 1975. On the quest for quality in the field bean,
p. 143-149. In: M. Milner (ed.). Nutritional improvem ent of food
legumes by breeding. Wiley, New York.
2. Bliss, F.A. and J.W .S. Brown. 1983. Breeding common bean
for improved quantity and quality of seed protein. Plant Breed.
Rev. 1:5 9-102 .
3. Dudley, J.W. 1982. Theory for transfer of alleles. Crop Sci.
22:631-637.
4. Ikahashi, H. 1982. A simulation study on balancing backcrosses
with selections in breeding for quantitative traits in self-polli-
inating crops. Japan J. Breed. 32:71-7 8.
5. Kelly, J.D. and F.A. Bliss. 1975. Heritability estimates of per
centage seed protein and available methionine and correlations
with yield in dry beans. Crop Sci. 15:753 -75 7.
6. Laurell, C.B. 1967. Quantitative estimation of proteins by elec-
tophoresis in antibody-containing agarose gel, p. 499 -5 02. In:
H. Peeters (ed.). Proteins in biological fluids, Vol. 14. Elsevier,
Amsterdam.
7. Laurell, C.B. 1972. Electroimmunoassay. Scand. J. Clin. Lab.,
Invest. (Suppl. 2) 124:21-3 7.
8. Leleji, O.I., M .H . Dickson, L .V. Crowder, and J.B. Bourke.
1972. Inheritance of crude protein percentage and its correla tion
with seed yield in beans, Phaseolus vulgaris L. Crop Sci. 12:168—
171.
9. Ma, Y. and F.A . Bliss. 1978. Seed proteins of the com mon bean.
Crop Sci. 18:431-43 7.
10. Mutschler, M.A. 1979. Genetic control o f globulin-1 seed protein
and its relationship to total protein content and quality in dry bean
{Phaseolus vulgaris L.) and male sterility in the dry bean (P.
vulgaris). PhD Thesis, University of W isconsin, Madison.
11. Mutschler, M .A. and F.A. Bliss. 1981. Inheritance of bean seed
globulin content and its relationship to protein content and quality.
Crop Sci. 21:2 89 -294.
12. Mutschler, M.A ., F.A. Bliss, and T .C. Hall. 1980. Variation in
the accumulation of seed storage protein among genotypes of
Phaseolus vulgaris L. Plant Physiol. 65 :62 7-630 .
13. Osborne, T.B . 1894. The proteins of the kidney bean. J. Amer.
Chem. Soc. 16:703-712.
14. Rutger, J.N . 1970. Variation in protein content and its relation
to other characters in beans {Phaseolus vulgaris L.) , p. 59- 69 .
In: Rpt. 10th Dry Bean Res. Con f., Davis, Calif.
15. Sullivan, J.G . and F.A. Bliss. 1983. Genetic control of quanti
tative variation in phaseolin seed protein o f common bean, J.
Amer. Soc. Hort. Sci. 108:782-787.
16. Sun, S .M ., M.A. Mutschler, F.A. Bliss, and T.C. Hall. 1978.
Protein synthesis and accumulation in bean cotyledons during
growth. Plant Physiol. 61:9 18-92 9.
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J. Amer. Soc. Hort. Sci. 108(5):791-795. 1983.
Influence of Liming Rate on Holly, Azalea,
and Juniper Growth in Pine Bark
Grace A. Chrustic1 and Robert D. Wright2
Departme nt o f Horticulture, Virginia Polytechnic Institute a nd State University, Blacksburg,
VA 24061
Additional index words, lime, woody ornamentals, nursery crops, plant nutrition, Ilex crenata, Rhododendron obtusum,
Juniperus chinensis
Abstract. Rooted cuttings of Ilex crenata Thunb. ‘Helleri’, Rhododendron obtusum Planch. ‘Rosebud’, and Juniperus
chinensis L. ‘San Jose’ were grown in a 100% pine-bark medium amended with dolomitic limestone at 0 to 8 kg m-3
with resulting pH from 3.4 to 7.2. Except for juniper at 2 kg m“3, growth was not increased by liming, and 8 kg
m“3 tended to reduce shoot and root growth. This reduced growth was attributed in part to greater NH4 adsorption
by the bark, reducing the amount available for plant uptake, and a higher nitrification rate, leading to an elevated
N 03 to NH4 ratio in the medium. Liming pine bark to improve growth of these woody plants may be unnecessary.
Pine bark has become an important container medium due to
its desirable physical properties and its availability as a by
product of pulp and lumber industries. However, little infor
mation is available on the physical and chemical properties of
pine bark in relation to plant nutrition, especially in regard to
the optimum pH for plant growth. Milled pine bark has a pH of
about 4 .5 , and dolomitic limestone is usually added at 4 -6 kg
Received for publication February 2, 1983. This work was supported in part by
the Virginia Nurserymen’s Association. The cost o f publishing this paper was
defrayed in part by the payment of page charges. Under postal regulations, this
paper therefore must be hereby marked advertisement solely to indicate this fact.
Graduate Student.
2Associate Professor.
li
m -3 to adjust the pH to about 6.0. The advisability of this
addition is unknown, since studies evaluating the effects of pine-
bark pH on growth of woody nursery crops are lacking.
In organic soils, the pH levels for satisfactory growth have
been reported to be 1-1.5 units lower than values established
for mineral soils (9). Recent studies by Hipp and Morgan (7)
indicated that growth o f Nephrolepis exaltata ‘Rooseveltii’ in a
peat—perlite medium was greatest when pH was adjusted to 4 .0 —
5.0 . Further, maximum dry weight of N. exaltata ‘Compacta’
was obtained in a peat-p erlite medium unlimed (pH 3.6) or with
low lime rates (pH 5.5), compared to higher lime rates (5).
The purpose of the experiments reported herein was to eval
uate growth of 3 nursery crops as influenced by liming rate in
a pine bark medium.
Materials and Methods
Pine bark used in this study was primarily from Pinus taeda
L. and had a particle size distribution of 38% less than 0.05 mm
(U.S. Series sieve # 3 5 ), 28% between 0.05 and 1.19 mm (U.S.
Series sieve #1 6), 20% between 1.19 mm and 2.38 mm (U.S.
Series sieve #8), and 14% between 2.38 and 6.35 mm (U.S.
Series sieve #3 ), with a bulky density of 0.35 g cm-3 .
Expt. 7. Based on the results of a preliminary experiment,
pine bark was amended with dolomitic limestone at 0, 1, 2, 4,
and 8 kg m ~3 of dolomitic limestone. On September 3, 1981,
75 rooted cuttings of Rhododendron obtusum ‘Rosebud’ and Ilex
crenata ‘Helleri’ were potted into one-liter plastic pots contain
ing pine bark amended with the above lime rates. The plants
were greenhouse-grown in a randomized complete block design
with 5 replications and 3 plants per treatment per replication.
Each plant was fertilized with 300 ml o f a nutrient solution
containing 100 ppm N as NH4N 03, 10 ppm P as H3P 04, 100
ppm K as K2S0 4, 70 ppm Ca as C aS04*2H20 , 25 ppm Mg as
M gS04*7H20, 5 ppm Fe as NaFeEDTA, and micronutrients
according to Hoagland and Amon (8). For azalea, the N and K
concentrations were changed to 35 ppm and 30 ppm, respec
tively. Both genera were fertilized every other day for 8 weeks.
Leachates were collected after surface application of 50 ml
of distilled water on September 9, and weekly thereafter from
one container per treatment per replication. The leachates were
filtered through Whatman # 1 filter paper, and the pH was de
termined. Leachates then were frozen for future N 03-N and
NH4-N analysis by ion selective electrodes, P determination
colorimetrically (14), and K determination by atomic absorption
spectroscopy.
On November 6, 1981, sterfis were cut just above the upper
roots, after which shoots and roots o f ‘Helleri’ holly and shoots
of ‘Rosebud’ azalea were rinsed in distilled water, dried at 70°
C, and weighed. Root-ball diameter of azalea was measured and
used as the parameter of root growth, since the medium could
not be completely separated from the roots. Nitrogen was de
termined by micro-Kjeldahl technique (12), P colorimetrically
(14), and K by atomic absorption spectroscopy.
Expt. 2. Expt. 2 was similar to Expt. 1 with the following
changes. Sixty-four, 10-cm rooted cutings of ‘Helleri’ holly and
Juniperus chinensis ‘San Jose’ liners were potted on February
18, 1982 in pine bark amended with dolomitic limestone at 0,
2, 4, or 8 kg m - 3 . Both genera received 300 ml of the previously
described nutrient solution for ‘Helleri’ holly, with the exception
that Ca and Mg were omitted. The plants were greenhouse-grown
for 12 weeks in a randomized complete block design with 4
replications and 4 plants per treatment per replication.
On February 25, and every 2 weeks thereafter, initial leachates
were taken by pouring 75 ml of distilled water onto the surface
of 4 containers from each of the 4 treatments (one from each
replication). Leachate and tissue samples were treated as in Expt.
1 nutrient analysis.
Results
Mean pH over time for both holly and azalea at 0, 1, 2, 4,
and 8 kg m ~3 ranged from 3.4 to 7.2, respectively (Table 1).
In Expt. 2, for both holly and juniper, treatments of 0, 2, 4,
and 8 kg m ~3 resulted in mean medium pH values ranging from
4.4 to 6.9 (Table 1). Changes in pH over time were 0.5 pH
units or less.
Holly shoot weight in Expt. 1 decreased as limestone additions
increased (Table 1). Shoot dry weight o f azalea also decreased
at 4 and 8 kg m ~3 of limestone. Holly root dry weight decreased
Table 1. Influence of dolomitic limestone rate on shoot and root growth
of holly, azalea and jun iper.
Lime rate Dry wt (g)
Expt. (kg m~ 3) PH Shoot Root
Holly Azalea Holly Azale az
03.4 2.41 1.90 0.37 7.9
14.1 2.37 1.98 0.34 7.9
24.6 2.32 1.92 0.30 7.5
45.9 2.08 1.80 0.26 5.6
87.2 2 . 0 0 1.63 0.24 4.9
Significance*
Linear 0 . 0 1 0 .0 1 0 .0 1 0 .0 1
Quadratic NS NS NS 0 .0 1
Holly Juniper Holly Juniper
04.4 5.15 7.80 1.09 1.73
25.4 5.05 8.69 0.90 1.89
45.9 4.19 8.15 0 . 8 6 1.57
86.9 3.19 7.25 0.72 1.58
Significance
Linear 0 . 0 1 NS 0 . 0 1 0.04
Quadratic 0.07 0.03 NS NS
zData given is for root-ball diameter (cm).
ySingle degree o f freedom com parisons. Level of probability value
above 10 % considered nonsignificant (n s ).
with increasing lime additions, and azalea ro ot-ball diameter
was reduced at 2, 4, and 8 kg m -3 . In Expt. 2, maximum shoot
and root dry weights o f holly and juniper occurred at the lower
lime rates, with the larger shoots and roots for juniper occurring
at 2 kg m ~3 (Table 1).
Shoot N, P, and K was generally higher at the lower lime
rates, with the exception o f juniper P and K (Expt. 2), (Table
2). Nutrient concentrations of medium leachates were also higher
at the lower lime rates. The N0 3-N level in the holly medium
leachate (Expt. 1) for weeks 2-5 was higher at the lower lime
rates (Figure la). In contrast, by week 8, N 0 3-N levels were
higher at the higher lime rates. However, NH4-N levels were
consistently higher throughout the experiment at the lower lime
rates (Fig. lb). Further, the ratio of N 0 3-N to NH4-N was
lower at the lower lime rates (Table 3). P (Fig. lc) and K (Fig.
Id) leachate levels for weeks 1-5 and 1-4, respectively, were
highest at the lower lime rates, whereas by week 8 the reverse
was true for P. Similar trends in nutrient leachate levels occurred
for azalea in Expt. 1 and for holly and juniper in Expt. 2, with
the exceptions that azalea N 0 3-N levels were higher at lower
pH levels throughout the experimental period and P levels did
not demonstrate a reverse response by week 8 (data not shown).
Discussion
Increasing the lime rate of a pine-bark medium generally de
creased dry weight, shoot tissue N, P, and K content, and me
dium leachate levels of N0 3, NH4, P, and K. This effect of
liming on growth concurs with the results of Hipp and Morgan
(7) and Gilliam et al. (5) for Nephrolepis, where maximum
growth was obtained from either nonlimed or low lime rates.
Differences in growth among the treatments may be attributed
to the variance in the medium leachate nutrient levels, in par
ticular, NQ3-N and NH4-N . Holly leachate N 0 3-N (for the
first 5 weeks) and the NH4-N concentrations throughout (Figures
la and lb ) were of greater magnitude at the lower lime rates.
CO N CEN T R AT IO N (pp m )
18 c
TIME (weeks)
Fig. 1. Influence of liming rate on leachate nutrient levels over time from ‘Helleri’ holly (Expt. 1). Mean separation at each date by Duncan’s
multiple range test, 5% level.
Table 2. Influence of dolomitic limestone rate on nutrient content of
holly, azalea and juniper shoots.
Expt. Species
Lime rate
(kg m“ 3)
Shoot content
(% dry wt)
N P K
1Holly 02.7 0.33 1 . 2
12.5 0.35 1 . 1
2 2 . 6 0.33 1 . 1
42.5 0.30 0.9
82.3 0.25 0 . 8
Significance2
Linear 0.04 0 . 1 0 . 0 1
Quadratic NS 0 .0 1 NS
Azalea 01.7 0.28 0.9 0
11.7 0.27 0.95
21.7 0.38 0.99
41.4 0.25 0.61
81.3 0.24 0.60
Significance
Linear 0 . 0 1 0 . 0 1 0 . 0 1
Quadratic NS NS 0 . 0 1
2Holly 02.4 0.58 2.4
22.3 0.54 2.3
42 . 2 0.54 2 . 2
82 . 0 0.42 2.3
Significance
Linear 0 . 0 1 0 . 0 1 0.06
Quadratic 0.08 NS 0.08
Juniper 01.7 0 . 2 2 1 . 2
21 . 8 0 . 2 2 1 . 2
4 1.7 0.23 1.3
81.4 0 . 2 2 1.3
Significance
Linear 0 . 0 1 NS NS
Quadratic 0 . 0 1 NS NS
zSingle degree of freedom com parisons. Levels of probability above
10% considered nonsignificant (n s ) .
The leachate N levels were reflected in the sequential decrease
in shoot tissue N levels as the lime rate increased (Table 2).
Niem iera and Wright (11), employing a sand culture, demon
strated that differences in substrate N levels in the range of those
occurring in this particular study can influence ‘Helleri’ holly
tissue N levels and shoot growth. Other investigators have re
ported that percentage of N in the leaves of 3 species of holly
was related to amount of N in the nutrient solution (2).
The fact that the ratio of N 03-N to NH4-N was lower at the
lower lime levels (Table 3) also could explain some of the dif
ferences in plant growth. Though plants can utilize both NH4
Table 3. Influence of dolomitic limestone rate on ratio of N 03-N to
NH4-N in leachates of holly and azalea at week 8 (Expt. 1) and
holly and jun iper at week 12 (Expt. 2).
Lime rate
(kg m~ 3)
Ratio N 0 3--N:NH4-N
Expt. 1 Expt. 2
Holly Azalea Holly Juniper
011 1 1
211 1 1
421 6 8
864 49 109
and N 03 forms of N, reports in the literature demonstrate the
preference of some woody species for NH4-N or at least for a
1 : 1 NH4-N :N 0 3-N ratio, as opposed to higher levels o f N 03-
N (1, 3, 6).
Lower amounts of leachate NH4 at the high lime rate could
result from volitalization losses (13) and the increased absorptive
capacity o f pine bark for NH4 at this pH level (4). Collectively,
these 2 chemical processes could account for the lower amounts
of N 0 3 for the first 5 weeks due to a loss of substrate for
nitrification. The reversal of N 03 levels in response to lime rate
by week 8 could be due to a more rapid increase in populations
of nitrifying bacteria at the higher lime rate (13). ThereforelSK>3-
N would increase at a more rapid rate over time at the higher
lime rates compared to the lower ones. This reasoning is further
supported by a more rapid decrease in NH4-N at the higher lime
rates at week 8.
Other factors such as low P and K leachate levels (Fig. lc
and Id) also may have contributed to plant growth reduction.
Medium pH influences the ionic form and the solubility of P.
When the pH of organic soils is raised above 5.8, phosphates
are rendered less available due to chemical precipitation as cal
cium phosphates (9, 10). Also, K has been shown to be adsorbed
to pine bark to a greater extent as pH increases (4).
The greatest single benefit of liming acid mineral soils is the
reduction of aluminum and manganese toxicity to plants (13).
Pine bark is inherently low in aluminum and manganese, and
therefore the toxicity potential is reduced. Further, the need to
lime pine bark to supply Ca and Mg does not appear necessary,
since leachates from pine bark receiving no lime and no Ca and
Mg (Expt. 2) contained 34 ppm Ca and 15 ppm Mg. Presumably
this was supplied from the bark and the water supply, which
contained 13 ppm Ca and 5 ppm Mg. Further experimentation
should be conducted to determine if applications o f Ca or Mg
over a 1- to 2-year period are necessary for plants grown in pine
bark.
We conclude that there is no advantage to liming pine bark
for growth of holly and azalea if all nutrients are supplied in
sufficient quantities and if no element is present in toxic con
centrations. More investigations are needed to determine if jun
iper requires additions of limestone at low rates (2 kg m-3 ) for
optimal growth.
Literature Cited
1. C olgrove, M .S ., J r., and A .N. Roberts. 1956. Growth o f the
azalea as influenced by ammonium and nitrate nitrogen. Proc.
Amer. Soc. Hort. Sci. 68 :522- 536.
2. Dunham, C.W. and D.V . Tatnall. 1961. Mineral composition of
leaves of three holly species grown in nutrient sand cultures. Proc.
Amer. Soc. Hort. Sci. 78 :564- 571.
3. Edw ards, J.H . and B.D. Horton. 1982. Interaction of peach seed
lings to N 03:NH4 ratios in nutrient solutions. J. Amer. Soc. Hort.
Sci. 107:142-147.
4. Foster, W .J., R .D . Wright, M .M . Alley, and T.H . Yeager. 1983.
Amm onium adsorption on a pine-bark growing medium. J. Amer.
Soc. Hort. Sci. 108:5 48-551.
5. Gilliam, C.H., D.J. Eakes, R.L. Shumak, andC .E. Evans. 1982.
Liming materials and rates for Boston ferns in a soilless medium.
I. Effects of pH. Comm un. Soil Sci. Plant Anal. 1 3:259-266.
6. Gilliam, C.H ., T.A. Fretz, and W.J. Sheppard. 1980. Effect of
nitrogen form and rate on elemental content and growth of pyr-
acantha, cotoneaster and weigela. Scientia Hort. 13:173—179.
7. Hipp, B.W . and D. Morgan. 1980. Influence of medium pH on
growth of ‘Roosevelt’ ferns. HortScience 15:196.
8. Hoagland, D.R. and D.I. Amon. 1950. The water culture method
for growing plants without soil. Calif. Agr. Expt. Sta. Cir. 347.
9. Lucas, R.E. and J.R. Davis. 1961. Relationship between pH
values of organic soils and availability of 12 nutrients. Soil Sci.
92:177-182.
10. Moser, F. 1943. Calcium nutrition at respective pH levels. Soil
Sci. Soc. Amer. Proc. 17:339-344.
11. Niemiera, A.X . and R.D. Wright. 1982. Growth of Ilex crenata
Thun b. ‘Helleri’ at different substrate nitrogen levels. Hort-
Science 17:354-3 55.
12. Peterson, H.C. and G. Chesters. 1964. A reliable total nitrogen
determination of plant tissue accumulating nitrate nitrogen. Agron.
J. 56 :89-90.
13. Tisdale, S.L. and W.L. Nelson. 1975. Soil fertility and fertilizers.
Macmillan, New York.
14. Watanabe, F.S. and S.R. Olsen. 1965. Test of an ascorbic acid
method for determining phosphorus in water and N aH C03 extracts
from soil. Soil Sci. Soc. Amer. Proc. 29:677-6 78 .
J• Amer. Soc. Hort. Sci. 108(5):795—800. 1983.
Inhibition of Shoot Growth in Greenhouse-grown
Tomato by Periodic Gyratory Shaking
Joan C. Heuchert and Cary A. Mitchell1
Departm ent o f Horticulture, Purdue University, West Lafayette, IN 47907
Add itio nal index words, seismomorphogenesis, Lycopersicon esculentum
Abstract. Seedlings of tomato (Lycopersicon esculentum Mill. cv. Rutgers) were agitated periodically on a gyratory
shaker. Shaking plants at 175 rpm for 5 minutes once daily during the winter reduced leaf area, stem length, and
water content and dry weight of both leaves and stems. This treatment was ineffective when applied during the
summer. Five- to 20-minute treatments applied 2 or 3 times daily reduced growth during either season, but were
more effective during winter. Responses were independent of the time of day at which treatment took place. Leaf
area, stem length, water content of leaves and stems, leaf dry weight, and specific stem water content were reduced
progressively relative to undisturbed controls as the shaking rate increased from 125 to 175 rpm during the winter.
Leaf area, specific leaf water content, and specific stem water content were reduced by shaking at 44% of full summer
sunlight, but not at 31% or 17%. Shaking enhanced specific stem weight only at 44% light, whereas stem length was
reduced most by shaking at 17% light. Differences in relative plant response to shaking between summer and winter
remained even when seasonal differences in solar flux density were minimized by use of shadecloth during the summer.
Plants subjected to wind action often have shorter stems, smaller
leaves, and lower fresh and dry weights than wind-protected
plants (2, 9, 10, 21). Wind-induced growth changes have been
associated with enhanced respiration and transpiration, as well
as with decreased photosynthesis and water content (1, 4, 5, 6,
13, 18, 19). The mechanical aspect of wind action on plant
development has been investigated using a variety of mechanical
treatments including air currents, shaking, flexing, rubbing, and
water spray (5, 8, 11, 15, 17, 20). Periodic disturbance applied
with a gyratory shaker affects plants in ways similar to those
resulting from wind action (15). Time o f day o f treatment did
not alter the response to shaking of tomato (15) or sweetgum
(16), whereas chrysanthemum was dwarfed more by shaking at
0800 h r than at 1600 or 2400 h r (3). Threshold shaking duration
for chrysanthemum was 30 sec at 200 rpm; and 2 or 3 daily
treatments of 2- to 5-min duration each time were more effective
than one daily treatment (3).
Tomato plants shaken for 30 sec once daily at 282 rpm were
smaller than undisturbed controls after 2 weeks o f treatment (15).
Tomato appears to be more sensitive than chrysanthemum to
periodic shaking. This investigation provides a systematic char
acterization of tomato response to shaking by varying the timing,
duration, and intensity of treatment during the summer and win
ter seasons.
Received for publication November 22, 1982. Purdue Agricultural Experiment
Station Journal Paper 9002. Project conducted by the senior author in partial
fulfillment of the MS degree. Project supported in part by NASA grant NSG
7278 to the junior author. The cost of publishing this paper was defrayed in
part by the payment of page charges. Under postal regulations, this paper there
fore must be hereby marked advertisement solely to indicate this fact.
Associate Professor.
Materials and Methods
Cultural system and practices. Seeds of ‘Rutgers’ tomato
were germinated in Petri dishes and transplanted, 4 per pot, to
12.7-cm diameter standard plastic pots in a greenhouse. The
growth medium consisted of 1 soil : 2 peat : 2 perlite (by vol
ume), pH 6.2. Nutrients were incorporated at the following
concentrations in g m -3 of the final mixture: trace element mix,
75; K N 03, 597; M g S04, 597; and superphosphate (0-4 6 -0),
896. Pots were irrigated with tap water supplemented with 200
mg liter - 1 each of K and N (as N 03- ) at pH 6.8. Drip irrigation
was used to prevent uncontrolled mechanical disturbance of plants
during watering (relative to overhead spray). Five days after
emergence, seedlings were thinned to one per pot, selected for
uniformity, and arranged in a randomized complete block de
sign, and experimental treatments were initiated. Each treatment
group contained 12 plants. Experiments were conducted under
the natural photoperiods of winter (9.5 to 10.5 hr day- 1 ) or
summer (13.5 to 14.5 hr d ay- 1 ). Winter experiments received
an incandescent nightbreak from 2200 to 0200 h r daily. Shad
ecloth, which attenuated solar flux density 56%, covered the
greenhouse during summer experiments; it was not used during
winter experiments. This procedure approximately equalized both
total solar energy (225 to 2800 nm) within the greenhouse (14,130
J cm -2 for 22 days during summer vs. 16,590 J cm -2 for 22
days during winter) and average daily solar flux density (640
± 260 Jem-2 day-1 during summer vs. 750 ± 420 J cm -2
day -1 during winter) for the exact periods of experimentation
(Eppley pyranometer). A diurnal temperature regime of 27°C
days/23° nights was maintained in the greenhouse during winter,
whereas maximum summer temperatures were 29° to 32° (main
