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A THESIS FOR THE DEGREE OF MASTER OF SCIENCE

Vegetative Growth and Flowering of Dianthus,

Zinnia, and Pelargonium as Affected by Night

Interruption at Different Timings

야파 처리 시간대에 따른 죽, 백일홍, 제라늄의 생장과 개화 반응

BY

YU JIN PARK

FEBRUARY, 2013

MAJOR IN FLORICULTURE AND LANDSCAPE PLANTS

DEPARTMENT OF PLANT SCIENCE

THE GRADUATE SCHOOL OF SEOUL NATIONAL UNIVERSITY

Vegetative Growth and Flowering of Dianthus, Zinnia, and Pelargonium as Affected by Night Interruption at

Different Timings

UNDER THE DIRECTION OF DR. KI SUN KIM SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL

OF SEOUL NATIONAL UNIVERSITY

BY YU JIN PARK

MAJOR IN FLORICULTURE AND LANDSCAPE PLANTS DEPARTMENT OF PLANT SCIENCE

THE GRADUATE SCHOOL OF SEOUL NATIONAL UNIVERSISTY

JANUARY, 2013

APPROVED AS A QUALIFIED THESIS OF YU JIN PARK FOR THE DEGREE OF MASTER OF SCIENCE

BY THE COMMITTEE MEMBERS

FEBRUARY, 2013

CHAIRMAN

Jung Eek Son, Ph.D.

VICE-CHAIRMAN

Ki Sun Kim, Ph.D.

MEMBER Changhoo Chun, Ph.D.

i

Vegetative Growth and Flowering of Dianthus,

Zinnia, and Pelargonium as Affected by Night

Interruption at Different Timings

Yu Jin Park

Department of Plant Science

The Graduate School of Seoul National University

ABSTRACT

Influences of night interruption (NI) application timings were examined on

vegetative growth and flowering of Dianthus chinensis (long-day plant, LDP),

Zinnia elegans (short-day plant, SDP), and Pelargonium zonale (day-neutral

plant). The experiments were conducted both in a greenhouse and in a growth

chamber. In both experiments, the plants were grown under 9 hour photoperiod

[short-day (SD) condition] or 9 hour photoperiod plus 4 hour NI with low light

intensity at 3-5 mmol·m-2·s-1. The NI was employed at 18:00-22:00 HR (NI18),

22:00-02:00 HR (NI22), and 02:00-06:00 HR (NI02). Net photosynthesis of

Dianthus during the NI period was determined in the growth chamber experiment.

In Dianthus, node number increased more rapidly in all NI treatments regardless

of the timing of NI. Zinnia were shorter under NI than under SD, with those

grown under NI02 being shortest. In Pelargonium, leaves of the plants grown

under NI02 were produced more slowly than those of the plants under NI18 and

ii

NI22. For these three species, dry weights of the plants under NI were not

significantly different from those of the plants under SD. The NI had no effect on

net photosynthesis of Dianthus. Flowering of Dianthus was hastened by all NI

treatments, but the effect was higher in NI02 than in NI18 or NI22. Zinnia

flowered later under NI02 than under NI22 or NI18. Flowering of Pelargonium

was not affected by NI application timing. These results indicate that NI02 was

most effective in promoting flowering in Dianthus (LDP) or inhibiting flowering

in Zinnia (SDP). However, the NI had no significant effect on net photosynthesis

and subsequent growth promotion in herbaceous plants.

Keywords: flowering, herbaceous plants, night interruption, photoperiod,

photosynthesis, vegetative growth

Student number: 2011-21206

iii

CONTENTS

ABSTRACT ················································································ i

CONTENTS ···············································································iii

LIST OF TABLES ········································································ iv

LIST OF FIGURES ·······································································v

INTRODUCTION ·········································································1

LITERATURE REVIEW ·································································4

MATERIALS AND METHODS ·························································7

RESULTS················································································· 10

DISCUSSION ············································································ 18

LITERATURE CITED ·································································· 22

ABSTRACT IN KOREAN ····························································· 27

iv

LIST OF TABLES

Table 1. Effects of night interruption (NI) application timings on height, number

of nodes or leaves on the main stem, and dry weight of Dianthus, Zinnia, and

Pelargonium at 3, 1, and 8 weeks after the treatment, respectively, during their

vegetative growth ····································································· 11

Table 2. Effects of night interruption (NI) application timings on days to visible

bud (VB) and flowering, number of nodes or leaves at flowering, number of

flowers, and flower diameter in Dianthus, Zinnia, and Pelargonium ·········· 16

v

LIST OF FIGURES

Fig. 1. Effects of night interruption (NI) application timings on vegetative growth

in (A) Dianthus, (B) Zinnia, and (C) Pelargonium······························ 12

Fig. 2. Changes in net photosynthetic rate (An) of Dianthus during the night

interruption (NI) period ······························································ 13

Fig. 3. Effects of night interruption (NI) application timings on flowering of (A)

Dianthus, (B) Zinnia, and (C) Pelargonium ······································· 15

1

INTRODUCTION

Plants have been classified based on their photoperiodic flowering responses.

Long-day plants (LDP) including Dianthus chinensis (Erwin and Warner, 2002),

Campanula carpatica (Whitman et al., 1998) and Salvia farinacea (Mattson and

Erwin, 2005) flower or flower earlier only when the night length is less than

some critical duration, whereas short-day plants (SDP) including Zinnia elegans

(Boyle and Stimart, 1983), Dolichos lablab (Keatinge et al., 1998) and Celosia

argentea (Piringer and Borthwick, 1961) do so only when the night length is

longer than some critical length (Runkle et al., 2012). Day-neutral plants (DNP),

such as Pelargonium zonale (Runkle and Fisher, 2004), Dimorphotheca sinuate

(Van Rooyen et al., 1991) and Linaria maroccana (Mattson and Erwin, 2005),

flower irrespective of photoperiod (Runkle et al., 2001). Photoperiodic flowering

is regulated by the length of the uninterrupted dark night (Runkle et al., 2012).

Photoperiod has often been controlled artificially to promote or inhibit flowering

(Blanchard and Runkle, 2010; Kim et al., 2011a; Mattson and Erwin, 2005;

Runkle et al., 1998). Under short-days (SD), night-interruption (NI) breaks up a

long dark period, simulating long-day (LD) conditions for plants (Vince-Prue

and Canham, 1983). NI has been used for preventing or delaying flowering of

SD herbaceous plants, such as Chrysanthemum × grandiflorum (Blanchard and

Runkle, 2009), and Kalanchoe blossfeldiana (Vince-Prue, 1975), and

accelerating flowering of LD herbaceous plants including Coreopsis grandiflora

(Runkle et al., 1998), Eustoma grandiflorum (Yamada et al., 2009), Cyclamen

persicum (Kang et al., 2008), and Petunia × hybrid (Blanchard and Runkle,

2

2010).

Although the small increase in light integral caused by NI at low light

intensity is often assumed to have a negligible effect on net photosynthesis and

subsequent growth promotion, tomato exhibited an increase in plant dry weight

under LD when low light intensity lighting at 3-5 mmol·m-2·s-1 was used to

extend daylength from 8 h to 16 h as a result of a reduction in dark respiration

during LD lighting (Adams et al., 2008). Cymbidium was also shown to

photosynthesize when 4 h NI with 3-7 mmol·m-2·s-1 was given during the night

period (Kim, 2012), suggesting that the increased growth and hastened flowering

of Cymbidium under NI (Kim et al., 2011b) can be attributed to the increased net

photosynthesis during NI period. However, the direct NI effect on

photosynthesis and vegetative growth promotion has not been more determined

in other herbaceous plants.

The NI effect on flowering promotion in LDP and flowering inhibition in

SDP varies depending on NI application timing during the night and higher

flowering responsiveness has often been achieved when NI was applied in the

middle of a 12 to 16 h dark period in various species (Thomas and Vince-Prue,

1997). NI from 22:00 to 02:00 HR has usually been applied to both SDPs and

LDPs in commercial greenhouse production (Runkle and Fisher, 2004). However,

the most effective NI application timing in a 16 h dark period can differ among

species, suggesting that the best time to give a NI is not necessarily in the middle

of night (Thomas and Vince-Prue, 1997). To effectively regulate flowering, NI

application timing should be determined depending on plant species. Thus, the

objectives of this study were to examine whether NI can promote the vegetative

3

growth of selected LDP, SDP, and DNP by increasing photosynthesis, and to

determine how NI application timing affects their vegetative growth and

flowering.

4

LITERATURE REVIEW

Night Interruption (NI)

Photoperiod is often manipulated to induce or prevent flowering in

photoperiodic species (Blanchard and Runkle, 2010). Time to flowering was

reduced by day-extension in Viola × wittrockianan (Runkle and Heins, 2003) and

Tecoma stans (Torres and Lopez, 2011). Alternatively, NI effectively breaks up

the long dark period resulting in modified LD conditions for plants (Vince-Prue

and Canham, 1983). The NI effect on flowering is most evident with SDPs, in

which it inhibits flowering by a very short exposure of light during the night

(Thomas and Vince-Prue, 1997). Most SDPs including Kalanchoe, Pharbitis and

Xanthium remain vegetative when illuminated for 0.5 h or less during the middle

of night (Vince-Prue, 1994). NI has been effective for accelerating the flowering

of LDPs including Campanula carpatica (Whitman et al., 1998), Eustoma

grandiflorum (Yamada et al., 2009), and Petunia × hybrid (Blanchard and

Runkle, 2010). To promote flowering, LDPs often require longer times of light

exposure (Thomas and Vince-Prue, 1997). A 4 h NI from 22:00 to 02:00 HR

generally is recommended to induce flowering in several genera of LDPs

including Campanula, Coreopsis, and Lavandula (Damann and Lyons, 1996;

Mastalerz, 1977; Whitman et al., 1996, 1997).

Flowering Response to NI Application Timing

NI effects on flowering promotion in LDPs and flowering inhibition in SDP s

varied depending on its application timing during the night (Thomas and Vince-

5

Prue, 1997). In various SDPs and LDPs, NI was usually most effective in the

middle of 12 to 16 h dark period (Thomas and Vince-Prue, 1997). The NI effect

on flowering suppression in Kalanchoe (SDP) was highest in the middle of the

night (at 7 h into 15 h night) (Vince-Prue, 1975), and flowering promotion in

Fuchsia (LDP) was also highest near the middle of night (at 8 h into 16 h night)

(Vince-Prue, 1975). Thus, the action of light was thought to divide the long night

into two periods of darkness, each of which would be shorter than the critical

(Thomas and Vince-Prue, 1997). However, this speculation is not appropriate,

since NI application timing providing maximum responsiveness was not altered

by prolonging the dark period. In experiments with the SDPs of Pharbitis and

Xanthium in non-24 h cycles, for example, NI application timing for maximum

responsiveness still occurred at 8-9 h after the beginning of a 40-48 h night,

despite the fact that the remaining 30-40 h period of unbroken darkness was far

longer than the critical night length (Salisbury and Ross, 1991). LDP such as

Hyoscyamus niger (Hsu and Hamner, 1967) and Lolium temulentum (Vince-Prue,

1975) were found to behave in a similar way. Thus, NI response might be a

transient period of sensitivity to light, which is related in time to the beginning

of the dark period (Thomas and Vince-Prue, 1997).

A circadian rhythm in the sensitivity to NI is evident in many plants

(Lagercrantz, 2009) including the SDPs of Perilla (Carr, 1952) and Kalanchoe

blossfeldiana (Thomas and Vince-Prue, 1997), and the LDPs of Hyoscyamus

niger (Hsu and Hammer, 1967) and Lolium temulentum (Perilleux et al., 1994).

The most effective NI application timing on flowering promotion or flowering

inhibition during dark period was determined by the time when a particular light

6

sensitive phase of a circadian rhythm coincided with an external light signal

(Thomas and Vince-Prue, 1997). Furthermore, the most effective timing was not

necessarily in the middle of a long dark period, and further it varied considerably

with plant species (Thomas and Vince-Prue, 1997). The maximum NI effect on

flowering promotion in Lolium (LDP) occurred at 9 h after the beginning of the

16 h dark period, while that on flowering inhibition in Xanthium (SDP) or

Coleus (SDP) occurred at 6 h or 11 h after the beginning of the 16 h dark period,

respectively (Thomas and Vince-Prue, 1997).

Direct NI Effect on Photosynthesis

The additional light integral associated with NI at low light intensity is often

assumed to have a negligible impact on net photosynthesis and subsequent

growth promotion. In contrast, Cymbidium was shown to photosynthesize when

4 h NI with low light intensity at 3-7 mmol·m-2·s-1 was given during the night

period (Kim, 2012), suggesting that the increased growth and hastened flowering

of Cymbidium (Kim et al., 2011b) under NI can be attributed to a direct effect of

LD lighting through an increased net photosynthesis. Adams et al. (2008)

showed that the relationship between photosynthetic photon flux (PPF) and net

photosynthesis was not linear at low light intensities, and therefore low intensity

LD lighting at 3-5 mmol·m-2·s-1 can offset respiration efficiently in tomato.

Hofstra et al. (1969) also reported that low intensity lighting at 13 mmol·m-2·s-1

during the night could be used efficiently to offset respiration in cocksfoot.

However, the direct NI effects on photosynthesis and subsequent growth

promotion have not been determined in herbaceous floricultural crops.

7

MATERIALS AND METHODS

Plant and Growth Conditions

The experiments were conducted both in a greenhouse and in a growth

chamber. In the greenhouse experiments, Dianthus chinensis ‘Diana’, Zinnia

elegans ‘Dream Land’, and Pelargonium × hortorum ‘Maverick Red’ plugs

[288-cell size (6 mL volume)] with 6-7 nodes, 4 true leaves, and 6-7 true leaves,

respectively, were purchased from Synnong Floricultural Seedling Co., Ltd.

(Anseong, Korea). Plants of the three species were transplanted into 10 cm

plastic pots filled with commercial potting medium (Sunshine Mix #1, Sun-Gro

Horticulture, Bellevue, WA, USA) and then grown in a greenhouse at the

Experimental Farm, Seoul National University, in Suwon, Korea. The plants

were drip irrigated twice a week with tap water and fertilized weekly with a

nutrient solutions of 1.0 dS·m-1 from Technigro 20N-9P-20K Plus fertilizer

(Sun-Gro Horticulture). Average day/night temperatures inside the greenhouse

were 19 ± 5/13 ± 1°C. Similar experiments were conducted in a growth chamber

at a constant temperature of 23°C. Overhead irrigation was employed to the

plants grown in the growth chamber.

NI Treatment

In both experiments, the plants were applied with NI using a white

fluorescent lamp (AL-2220D; A-lim Industrial Co., Ltd., Incheon, Korea) at 3-5

mmol·m-2·s-1. In the greenhouse experiments, plants were provided by 9 h

ambient light and covered with opaque black cloth daily from 17:00 to 08:00 HR.

8

The mean photosynthetic daily light integral (DLI) was 6.5 mol·m-2·s-1. In the

growth chamber experiments, plants were grown under a mean PPF of 130 mmol

·m-2·s-1 provided by white fluorescent (FLR40EX-W/A; Osram Korea, Ansan,

Korea) and metal halide lamps (MH 250W; Hanyoung Electric Co., Gwangju,

Korea) with a 9 h photoperiod from 08:00 to 17:00 HR. The light intensities

were measured with a line quantum sensor (Apologee Instruments, Inc., Logan,

UT, USA). During the dark period, NI for 4 h was employed at 18:00-22:00 HR

(NI18), 22:00-02:00 HR (NI22), and 02:00-06:00 HR (NI02). Control plants

were grown under an uninterrupted 15 h dark period.

Data Collection and Analysis

Vegetative growth was determined as number of nodes or leaves, plant height,

and dry weight. Plant height was measured from the ground to the uppermost

shoot or flower. Plant dry weight was determined after drying the plants in an

oven at 80°C for 5 days. At flowering, nodes or leaves on the main stem below

the first flower were counted. Days to visible bud (VB), days to flower from the

start of the treatments, number of flowers per plant, and flower diameter were

measured.

Gas exchanges of Dianthus during the NI period were measured with three

replicated plants per treatment at 3-5 weeks after the treatment during the growth

chamber experiments using a portable photosynthesis system (Li 6400, Li-Cor

Co., Inc., Lincoln, NE, USA) equipped with an infrared gas analyzer. Fifth

mature leaf from the base of the main stem was clamped onto 0.79 cm2 top clear

chamber. The light intensity illuminated during NI was 3-5 mmol·m-2·s-1 and the

9

leaf block temperature was kept at 23°C. Relative humidity in the leaf chamber

ranged between 45 and 65%, and the reference CO2 concentration was set to 500

mmol·mol -1.

The experiments were employed in a completely randomized design. Forty

plants from each species were randomly arranged within benchs for each

treatment: they were used for weekly growth evaluation and for dry weight

measurement. Statistical analyses were performed using the SAS system for

window V8 (SAS Inst. Inc., Cary, NC, USA). Differences among the treatment

means were assessed by Tukey’s honestly significant difference test at P < 0.05.

Regression and graph module analysis were performed using Sigma Plot

software (Systat Software, Inc., Chicago, IL, USA).

10

RESULTS

Vegetative Growth

Dianthus had more nodes under NI than under SD at 3 weeks after the

treatment in both experiments (Table 1). The number of nodes was not

significantly different between NI application timings. Plants grown under NI

appeared to be taller irrespective of NI application timings than under SD in both

experiments although no statistical differences were found among the treatments

in the greenhouse experiments (Fig. 1).

Zinnia were shorter under NI than under SD, and those grown under NI02

were shortest at 1 week after the treatment in both experiments (Table 1, Fig. 1).

The number of nodes was not significantly affected by NI.

At 8 weeks after the treatment, Pelargonium were taller under NI irrespective

of NI application timings than under SD in the greenhouse experiments, whereas

in the growth chamber experiments, only the plants grown under NI02 were

taller than under the other treatments (Table 1). The number of leaves decreased

under NI in both experiments. Plants under NI02 had less leaves than under

NI18 or NI22 in the greenhouse experiments, whereas in the growth chamber

experiments, the number of leaves was not significantly different according to

NI application timings.

For the three species, dry weights of the plants under NI were not

significantly different from those of the plants under SD (Table 1). The effects of

NI on net photosynthesis of Dianthus were not observed (Fig. 2).

11

Table 1. Effects of night interruption (NI) application timings on height, number

of nodes or leaves on the main stem, and dry weight of Dianthus, Zinnia, and

Pelargonium at 3, 1, and 8 weeks after the treatment, respectively, during

their vegetative growth.

NIz

Greenhouse Growth chamber

Plant

height

(cm)

No. of

nodes

No. of

leaves

Dry

weight

(g)

Plant

height

(cm)

No. of

nodes

No. of

leaves

Dry

weight

(g)

Dianthus chinensis ‘Diana’

SD 11.60 ay 8.6 b –x 0.50 a

9.36 b 11.3 b – 0.27 a

NI18 12.48 a 10.3 a – 0.41 a

9.82 a 12.3 ab – 0.26 a

NI22 12.42 a 10.8 a – 0.46 a

10.16 a 12.6 a – 0.22 a

NI02 12.67 a 10.8 a – 0.39 a

12.68 a 13.0 a – 0.26 a

Significance NS *** – NS

*** ** – NS

Zinnia elegans ‘Dream Land’

SD 9.33 a 3.8 a – 0.21 a

11.19 a 4.0 a – 0.31 a

NI18 8.88 ab 3.5 a – 0.24 a

10.36 ab 4.0 a – 0.22 a

NI22 8.50 ab 3.2 a – 0.17 a

10.27 ab 4.0 a – 0.34 a

NI02 7.71 b 3.2 a – 0.34 a

9.73 b 4.0 a – 0.25 a

Significance * NS – NS

** NS – NS

Pelargonium × hortorum ‘Maverick Red’

SD 25.48 b – 24.9 a 5.92 ab

23.75 ab – 19.9 a 4.19 a

NI18 28.49 a – 24.3 ab 6.76 ab

23.21 b – 17.7 b 3.31 a

NI22 29.71 a – 21.8 ab 7.37 a

23.50 ab – 17.7 b 3.20 a

NI02 29.07 a – 21.3 b 5.48 b

25.38 a – 16.9 b 3.64 a

Significance *** – * * * – *** NS

zThe plants were grown under 9 h photoperiod [short-day (SD) condition] or 9 h

photoperiod plus 4 h NI with low light intensity at 3-5 mmol·m-2·s-1 during the

following different timings: 18:00-22:00 HR (NI18), 22:00-02:00 HR (NI22),

and 02:00-06:00 HR (NI02).

yMean separation within columns for each species by Tukey’s honestly

significant difference test at P < 0.05.

x–, not determined.

NS, *, **, *** Non-significant or significant at P < 0.05, 0.01, or 0.001,

respectively.

12

Fig. 1. Effects of night interruption (NI) application timings on vegetative

growth in (A) Dianthus, (B) Zinnia, and (C) Pelargonium. The plants were

grown in a growth chamber under 9 h photoperiod [short-day (SD) condition]

or 9 h photoperiod plus 4 h NI with low light intensity at 3-5 mmol·m-2·s-1

during the following different timings: 18:00-22:00 (NI18), 22:00-02:00

(NI22), and 02:00-06:00 (NI02). Photographs were taken 3, 1, and 8 weeks

after the treatment for Dianthus, Zinnia and Pelargonium, respectively.

A

B

C

SD NI18 NI22 NI02

13

Relative time (h) to NI

-1 0 1 2 3 4 5

An (m

mol C

O2m

-2s-1

)

-5

-4

-3

-2

-1

0NI18

NI22

NI02

Fig. 2. Changes in net photosynthetic rate (An) of Dianthus during the night

interruption (NI) period. The plants were grown in a growth chamber under 9

h photoperiod plus 4 h NI with low light intensity at 3-5 mmol·m-2·s-1 during

the following different timings: 18:00-22:00 HR (NI18), 22:00-02:00 HR

(NI22), and 02:00-06:00 HR (NI02). Vertical bars are SE of the means (n = 3).

NI period

１４

Flowering

In Dianthus, days to VB were not affected by NI, but days to flowering were

reduced by NI when compared to SD (Fig. 3, Table 2). Plants under NI02

flowered earlier than those under NI18 or NI22 in both experiments. However,

days to flowering under NI was not decreased by the less formation of nodes

before flowering. The number of flowers was higher under NI compared to SD,

and more in NI02 than in NI18 or NI22 in both experiments. The flower diameter

was not significantly different among the treatments.

In Zinnia, days to VB and days to flowering were increased by NI, but the NI

effect was more apparent under NI02 than under NI22 and NI18 (Fig. 3, Table 2).

Plants under NI developed more nodes before flowering, but had fewer flowers

than under SD in both experiments. The number of nodes at flowering and the

number of flowers were not significantly different among the NI application

timings. In growth chamber experiments, the flower diameter under NI decreased

compared to SD, and that under NI02 was shortest. Flower diameter was not

affected by NI in the greenhouse experiments.

In Pelargonium, days to VB, days to flowering, number of flowers and flower

diameter were not affected by NI (Fig. 3, Table 2). Plants grown under NI had less

leaves at flowering than those under SD.

１５

Fig. 3. Effects of night interruption (NI) application timings on flowering of (A)

Dianthus, (B) Zinnia, and (C) Pelargonium. The plants were grown in a growth

chamber with 9 h photoperiod or 9 h photoperiod [short-day (SD) condition]

plus 4 h NI with low light intensity at 3-5 mmol·m-2·s-1 during the following

different timings: 18:00-22:00 (NI18), 22:00-02:00 (NI22), and 02:00-06:00

(NI02). Photographs were taken 11, 3, and 15 weeks after the treatment for

Dianthus, Zinnia, and Pelargonium, respectively.

SD NI18 NI22 NI02

A

B

C

16

Table 2. Effects of night interruption (NI) application timings on days to visible

bud (VB) and flowering, number of nodes or leaves at flowering, number of

flowers, and flower diameter in Dianthus, Zinnia, and Pelargonium.

Experiment NIz Days to

VB Days to

flowering

No. of nodes at

flowering

No. of leaves at flowering

No. of flowers

Flower diameter

(cm)

Greenhouse Dianthus chinensis ‘Diana’

SD 39.3 ay 54.2 a 12.9 a –x 3.1 b 6.17 a

NI18 36.8 a 49.5 b 12.6 a – 5.5 a 5.83 a

NI22 37.6 a 50.5 ab 12.8 a – 4.1 ab 5.88 a

NI02 36.2 a 49.3 b 12.1 a – 5.7 a 5.87 a

Significance NS ** NS – * NS

Zinnia elegans ‘Dream Land’

SD 14.1 c 29.0 c 5.3 b – 3.5 a 6.98 a

NI18 16.6 bc 34.9 b 5.2 b – 1.1 b 7.24 a

NI22 21.8 ab 41.4 a 6.1 ab – 1.0 b 7.11 a

NI02 24.1 a 42.9 a 6.8 a – 1.0 b 7.00 a

Significance *** *** *** – *** NS

Pelargonium× hortorum ‘Maverick Red’

SD 79.3 ab 85.3 ab – 30.3 a 45.7 a 11.13 a

NI18 79.0 b 84.8 ab – 29.7 a 46.4 a 10.38 a

NI22 79.8 ab 84.3 b – 23.7 b 46.4 a 10.58 a

NI02 82.5 a 87.2 a – 23.9 b 30.3 a 10.08 a

Significance NS NS – *** NS NS

Growth Dianthus chinensis ‘Diana’

chamber SD 64.3 a 82.3 a 17.0 a – 1.8 b 3.76 a

NI18 62.6 a 77.7 ab 17.0 a – 2.9 ab 3.31 b

NI22 61.3 a 75.5 ab 16.7 a – 3.5 ab 3.54 ab

NI02 55.8 a 69.1 b 16.2 a – 4.8 a 3.58 a

Significance NS * NS – ** NS

Zinnia elegans ‘Dream Land’

SD 13.4 c 24.9 c 5.4 b – 2.2 a 7.73 a

NI18 20.7 b 37.9 b 7.6 a – 1.0 b 6.51 ab

NI22 22.6 ab 38.6 b 7.7 a – 1.1 b 6.45 ab

NI02 24.4 a 42.5 a 7.3 a – 1.0 b 6.00 b

Significance *** *** *** – *** *

Pelargonium × hortorum ‘Maverick Red’

SD 97.6 a 100.4 ab – 38.1 a 19.2 a 9.10 a

NI18 91.1 b 95.6 b – 26.8 b 30.8 a 9.51 a

NI22 95.3 ab 99.1 ab – 29.5 b 24.0 a 9.29 a

NI02 99.1 a 103.7 a – 29.1 b 21.8 a 9.16 a

Significance NS NS – ** NS NS

17

zThe plants were grown under 9 h photoperiod [short-day (SD) condition] or 9 h

photoperiod plus 4 h NI with low light intensity at 3-5 mmol·m-2·s-1 during the

following different timings: 18:00-22:00 HR (NI18), 22:00-02:00 HR (NI22), and

02:00-06:00 HR (NI02).

yMean separation within columns for each species by Tukey’s honestly significant

difference test at P < 0.05.

x–, not determined.

NS, *, **, *** Non-significant or significant at P < 0.05, 0.01, or 0.001,

respectively.

18

DISCUSSION

Regardless of NI application timings, LD conditions created by NI changed

node number, plant height, or leaf production rate of Dianthus, Zinnia, and

Pelargonium (Table 1). In Tecoma stans (LDP), plant height and node number

increased as photoperiod increased from 9 to 16 h (Torres and Lopez, 2011).

Zinnia elegans (SDP) grown under weakly inductive photoperiods (14 to 14.5 h)

were taller than those grown under strongly inductive photoperiods (10.5 to 11.5 h)

(Cerny et al., 2003). Photoperiod affects stem growth by modulating the rate of

internode extension or the number of nodes in plants (Thomas and Vince-Prue,

1997). The leaf production rate is also influenced by photoperiod (Adams and

Langton, 2005). Leaf initiation rate of Apium graveolens (SDP) was lower under

LD than under SD when day-extension lighting was used, whereas leaf production

rate in maize (LDP) was faster in longer photoperiod (Booij and Meurs, 1994). NI

had no effect on dry mass accumulation of Dianthus, Zinnia, and Pelargonium

(Table 1). NI lighting had a limited effect on the total carbon gain in

Chrysanthemum morifolium (Kjaer and Ottosen, 2011). There was no significant

difference in biomass accumulation of Tecoma stans across photoperiod with 2

mmol·m-2·s-1 day-extension lighting (Torres and Lopez, 2011). NI had no influence

on net photosynthesis of Dianthus (Fig. 2). This result is consistent to the

generally held view that light of approximately 3-5 mmol·m-2·s-1 is unlikely to

have any significant impact on net photosynthesis (Adams et al., 2008). Although

Cymbidium whose light compensation point is around 5-8 mmol·m-2·s-1 (Hew

et al., 1989) photosynthesized slightly under NI with 3-7 mmol·m-2·s-1 (Kim,

19

2012), Dianthus as one of sun plants that have higher light compensation point,

around 10-20 mmol·m-2·s-1 (Taiz and Zeiger, 2006), may require much higher

light intensities to promote photosynthesis. NI might have no direct effect on

photosynthesis and increased carbon accumulation in Dianthus, Zinnia, and

Pelargonium and the changes in node or leaf number, and plant height of those

three herbaceous plants under NI can be attributed to the photoperiodic effect.

NI02 was more effective at accelerating flowering in Dianthus (LDP) or at

delaying flowering in Zinnia (SDP) than NI18 or NI22 (Table 2). In various SDPs

and LDPs, NI was usually most effective in the middle of 12 to 16 h dark period

(Thomas and Vince-Prue, 1997). The NI effect on flowering suppression of

Kalanchoe (SDP) was highest in the middle of the night (at 7 h into 15 h night)

(Vince-Prue, 1975). In Fuchsia (LDP), maximum acceleration of flowering under

NI was observed near the middle of night (at 8 h into the 16 h night) (Vince-Prue,

1975). The most effective timing of NI during dark period on flowering promotion

or flowering inhibition was determined by the time when a particular light

sensitive phase of a circadian rhythm coincided with an external light signal

(Thomas and Vince-Prue, 1997). Furthermore, the most effective timing is known

to vary among species, since it is not necessarily in the middle of a long dark

period (Thomas and Vince-Prue, 1997). The maximum NI effect on flowering

promotion in Lolium (LDP) occurred at 9 h after the beginning of the 16 h dark

period, while the maximum NI effect on flowering inhibition in Xanthium (SDP)

or Coleus (SDP) occurred at 6 h or 11 h after the beginning of the 16 h dark period,

respectively (Thomas and Vince-Prue, 1997). Flowering of Dianthus (LDP) was

promoted most and, similarly, flowering of Zinnia (SDP) was suppressed most

20

under NI02. The light sensitive phase of a circadian rhythm in Dianthus and

Zinnia might exist around from 02:00 to 06:00 HR.

Dianthus and Zinnia generally showed a quantitative flowering response to NI

application timing; as 4 h NI is given toward the end of the dark period, days to

flowering decreased and flower number increased in Dianthus (LDP), and days to

VB and days to flowering increased in Zinnia (SDP) (Table 2), indicating that

Dianthus and Zinnia were more sensitive to NI in later part of the night rather

than in early or middle part of the night. In this study, NI lighting was provided by

fluorescent lamps which emit blue and red (R) light and little far-red (FR) light,

and thus the emitted R:FR was high. In LDP, various experiments suggest that

flowering is promoted most when R light is delivered at least during the end part

of the night and FR light toward the beginning (Evans, 1976; Lane et al., 1965;

Thomas and Vince-Prue, 1997). In carnation (Harris, 1972), for example, R

became more promotive and FR became less so as the night proceeded. In Lolium,

when light was given in the early part of the night, the optimum lay towards low

R:FR, but the optimum was shifted towards higher R:FR when given throughout

the night. Together, the effective timing of NI in Dianthus and Zinnia might be

affected by the R:FR ratio of the NI light source.

In conclusion, in vegetative growth stage of these three herbaceous plants,

plant height, and the number of nodes or leaves were affected by prolonging

photoperiod with NI. NI02 was most effective in promoting flowering in Dianthus

(LDP) or inhibiting flowering in Zinnia (SDP), but flowering of Pelargonium

(DNP) was not affected by NI. However, since NI had no significant impact on

net photosynthesis and subsequent dry matter accumulation of Dianthus, Zinnia

21

and Pelargonium, more detailed experiment is needed to identify the effects of NI

on the vegetative growth promotion in herbaceous plants.

22

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27

ABSTRACT IN KOREAN

본 실험은 일장 반응을 달리하는 석죽(장일성 식물), 백일홍(단일성 식물),

제라늄(중간성 식물)을 이용하여 야파 처리 시간대가 생장 및 개화에 미치는

영향을 알아보고, 초화류에서 야파 처리가 광합성 촉진에 효과가 있는지

알아보고자 수행하였다. 야파 처리는 3-5μmol·m-2·s-1 저광도로 기존에 개화

조절에 가장 효과적이라고 알려진 22-02시와 18-22시, 02-06시에 처리하였고,

대조구는 9시간 일장 하에서 야파 처리를 하지 않았다. 실험은 유리 온실과

생육상에서 반복해서 수행하였고, 광합성 측정은 생육상에서 석죽을 대상으로

암기 중 야파 처리 동안의 광합성량 변화를 측정하였다. 각 작물의 영양 생장

시기동안 야파 처리구에서 뚜렷한 형태적 변화가 있었는데, 석죽은 야파 처리

시간대별 유의적 차이 없이 마디 수가 야파 처리구에서 단일 처리구에 비하여

증가하였다. 백일홍은 야파 처리구에서 초장 신장이 억제되는 경향을

보였는데 그 중, 2시 야파 처리구에서 초장이 가장 짧았다. 제라늄은 잎 수가

야파 처리구에서 단일 처리구에 비하여 감소하였고, 특히 2시 야파

처리구에서 잎 수가 가장 작았다. 그러나 세 가지 초화류 모두에서 식물의

건물중은 야파 처리구에서 유의적으로 증가하지 않았고, 석죽을 대상으로

광합성을 측정한 결과 야파 처리 기간 동안 호흡이 계속될 뿐 광합성량이

증가하지 않는 것을 확인할 수 있었다. 장일성 식물인 석죽은 야파 처리 시

개화가 촉진되고 꽃 수가 증가하였는데, 2시 야파 처리구에서 개화 소요

일수가 가장 단축되고 꽃 수가 가장 많았다. 단일성 식물인 백일홍은 야파

처리 시 화아 출현 일수와 개화 소요 일수가 유의적으로 증가하였는데, 역시

2시 야파 처리구에서 화아 출현과 개화가 가장 지연됨을 알 수 있었다.

중간성 식물인 제라늄에서는 화아 출현 일수, 개화 소요 일수, 꽃 수에서 모두

28

통계적 유의차가 나타나지 않았다. 이러한 결과를 통해 새벽 2시에 야파

처리를 하는 것이 장일성 식물 석죽의 개화 촉진과 단일성 식물 백일홍의

개화 억제에 가장 효과적임을 알 수 있었으며 3-5μmol·m-2·s-1 저광도 야파

처리는 초화류의 광합성에는 크게 영향을 미치지 않음을 알 수 있었다.

29