Effects of different light intensity on the growth of tomato seedlings in a plant factory

Abstract

Light-emitting diodes (LEDs) were the best artificial light source for plant factories. Red light-emitting diodes (LEDs, R) and blue light-emitting diodes (LEDs, B) were used to obtain different light intensities of uniform spectra, and the greenhouse environment was considered as a comparison. The results showed that root dry weight, shoot dry weight and stem diameter were superior in plant growth under 240 μmolm⁻²s⁻¹, additionally, the Dixon Quality Index (DQI) was also best. Under 240 μmolm⁻²s⁻¹, the net photosynthesis rate (Pn) was consistent with the greenhouse’s treatment, superior to other experimental groups. The results implied that the PPFD was more suitable for the cultivation of tomato seedlings under the condition of 240 μmolm⁻²s⁻¹, and can replace the greenhouse conditions so as to save energy and reduce emissions.

Full text

RESEARCH ARTICLE
Effects of different light intensity on the
growth of tomato seedlings in a plant factory
Yifeng Zheng
1
, Jun ZouID
1
*, Senmao Lin
2
, Chengcui Jin
2
, Mingming Shi
1
, Bobo Yang
1
,
Yifan Yang
1
, Dezhi Jin
1
, Rongguang Li
1
, Yuefeng Li
1
, Xing Wen
3
, Shaojun Yang
4
,
Xiaotao Ding
5
1School of Science, Shanghai Institute of Technology, Fengxian District, Shanghai, 201418, China,
2Tianchang Fu’an Electronic Co., Ltd., Tianchang, 239300, China, 3Shanghai Sansi Electronic Engineering
Co., Ltd., Shanghai, 201100, China, 4Shanghai Youyou Agricultural Technology Co., Ltd., Shanghai,
202150, China, 5Shanghai Academy of Agricultural Sciences, Shanghai, 201403, China
*zoujun@sit.edu.cn
Abstract
Light-emitting diodes (LEDs) were the best artificial light source for plant factories. Red light-
emitting diodes (LEDs, R) and blue light-emitting diodes (LEDs, B) were used to obtain dif-
ferent light intensities of uniform spectra, and the greenhouse environment was considered
as a comparison. The results showed that root dry weight, shoot dry weight and stem diame-
ter were superior in plant growth under 240 μmolm
-2
s
-1
, additionally, the Dixon Quality Index
(DQI) was also best. Under 240 μmolm
-2
s
-1
, the net photosynthesis rate (Pn) was consistent
with the greenhouse’s treatment, superior to other experimental groups. The results implied
that the PPFD was more suitable for the cultivation of tomato seedlings under the condition
of 240 μmolm
-2
s
-1
, and can replace the greenhouse conditions so as to save energy and
reduce emissions.
1. Introduction
Modern society is currently confronted with a challenging scenario known as a trilemma,
where three equally undesirable options exist: (1) a shortage of food, (2) limited resources, and
(3) environmental degradation. This trilemma is a global, as well as local and national, issue
exacerbated by urban population growth and a declining workforce. To address this trilemma,
it is crucial to develop transdisciplinary methodologies based on innovative concepts that sig-
nificantly enhance food yield and quality while minimizing resource consumption and envi-
ronmental harm compared to current plant production systems [1,2].
One such system with the potential to achieve this objective is plant factories [3,4] with arti-
ficial lighting (PFALs) [5]. PFALs offer several benefits, including high resource use efficiency,
increased annual productivity per unit of land, and the production of high-quality plants with-
out the need for pesticides [6,7]. Approximately 1.3 billion tons of food, which accounts for a
staggering one-third of the food produced worldwide for human consumption, is wasted
annually. Vegetables, in particular, have a high wastage rate. In developing countries, 40% of
this loss occurs during post-harvest and processing stages, while in industrialized nations, over
40% is wasted at the retail and consumer levels [8]. Food loss and waste lead to the substantial
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OPEN ACCESS
Citation: Zheng Y, Zou J, Lin S, Jin C, Shi M, Yang
B, et al. (2023) Effects of different light intensity on
the growth of tomato seedlings in a plant factory.
PLoS ONE 18(11): e0294876. https://doi.org/
10.1371/journal.pone.0294876
Editor: Yuan Huang, Huazhong Agriculture
University, CHINA
Received: September 9, 2023
Accepted: November 9, 2023
Published: November 29, 2023
Copyright: ©2023 Zheng et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the paper.
Funding: 1. Jun Zou, Shanghai Science and
Technology Committee (STCSM) Science and
Technology Innovation Program(Grant No.
22N21900400, Grant No. 23N21900100) 2. Bobo
Yang, Science and Technology Talent Development
Fund for Young and Middle-aged Teachers of
Shanghai Institute of Technology(Grant No.
ZQ2022-3).
Competing interests: The authors have declared
that no competing interests exist.

squandering of resources, including water, land, energy, labor, and capital. Additionally, they
contribute to greenhouse gas emissions, further exacerbating global warming and climate
change.
Hence, it is crucial to promote local production for local consumption, particularly for
fresh vegetables that have high water content. This approach helps in reducing vegetable loss
and conserving valuable resources. Fresh vegetables are susceptible to damage during trans-
portation due to their weight. It is well-established that plants with green leaves grow through
photosynthesis, which requires essential resources such as water, CO
2
, light energy, and inor-
ganic fertilizers containing 13 nutrient elements. Organic waste materials can be transformed
into inorganic fertilizers through decomposition using specific microorganisms. Heat energy
released from restaurants, offices, and various industrial facilities at temperatures of 30–60˚C
can be utilized for greenhouse heating in winter, food and material drying, and other applica-
tions. The cultivation of plants for food and various other purposes presents a significant
opportunity to reduce resource consumption and waste in urban areas [9].
There are two types of light sources available: natural and artificial. In the practical process
of plant factory production [10], which includes both planting and seedling cultivation [11],
reliance on natural light sources (such as sunlight) restricts the positioning of carriers like
seedbeds or trays. This limitation necessitates a single-layer placement mode to avoid shadow-
ing between plants, resulting in a larger utilization area for the facility. Additionally, consider-
ing the resource consumption associated with temperature, humidity, carbon dioxide control,
etc., the overall production costs are significantly increased [7]. In comparison, artificial light
sources offer several advantages. They can fulfill the light requirements of plants while
enabling three-dimensional planting, reducing the utilization area, and lowering production
costs. Among the various artificial light sources available, light-emitting diodes (LEDs) have
emerged as the primary choice in practical plant factory production. LEDs are highly efficient,
consume less energy, have a compact size, and boast a long lifespan.
When tomato seedlings are bred in plant factories, the light intensity, light quality ratio and
photoperiod of the artificial light source cannot be controlled in real time, and the tomato
seedlings can only be supplemented with fixed light intensity, fixed light quality ratio and fixed
photoperiod set in advance. In order to achieve the optimal Dixon Quality Index [12], tomato
seedlings need a large light intensity, but greater intensity may inhibit the growth of tomatoes.
Therefore, the quality of light intensity has a great influence on the growth and physiological
changes of tomato seedlings. When the light intensity is low, the plant is more susceptible to
light suppression, resulting in the phenomenon of excessive length and higher plant height.
Normally, the net photosynthetic rate (Pn) [11] is consistent with light intensity’s change.
There are some plants, such as tomatoes, cucumbers, and strawberries have evolved various
mechanisms, including morphological and physiological changes, in order to adapt to various
environments. These measures relieve the damage caused by excessive lighting, and ensure the
photosynthesis of plants [13]. The percentage absorption of blue or red light by plant leaves is
about 90% [14]. Therefore, blue and red light exert a significant influence on plant develop-
ment and physiology. The combination of red and blue light is increasingly being utilized in
both research and commercial horticulture due to their high photosynthetic efficiency at the
leaf level, both in the short-term [15] and long-term [16,17]. The absence of either the red or
blue light wavelengths [18] leads to photosynthetic inefficiencies. The combination of red and
blue light has demonstrated its effectiveness as a lighting source in promoting plant develop-
ment [19,20] and enhancing plant health [21,22]. The combination of red and blue light in a
7:3 ratio has been found to enhance the fresh weight and dry weight of various plant species,
including Lilium, Chrysanthemum, and tomato [23,24]. When cultured under R:B = 7:3 LED
light [25,26], the plants exhibited a higher specific leaf area [27,28], which could enhance light
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absorption. Additionally, the ratio of red to blue light at 7:3 [29,30] resulted in an increase in
leaf-level photosynthetic rate (Pn) [24,31].
Previous studies have primarily focused on examining the impact of varying light intensities
on plant growth and development in natural sunlight. However, limited information is avail-
able regarding the effects of different light intensities on plant growth and development when
exposed to a combination of red and blue light. What implications will different artificial light
intensities, particularly those involving red and blue light combinations, have on plant growth
and development? Furthermore, which artificial light intensity would be optimal for plant cul-
tivation? As a result, it is crucial to investigate the appropriate intensities of red and blue LEDs
in combination for industrialized production and to assess the diverse responses arising from
low and high light intensities in artificial conditions.
The tomato is a globally distributed crop that is cultivated year-round in China. Large-scale
production of young tomato plants predominantly occurs under controlled conditions to meet
the growing demand. Within controlled environments, additional lighting is commonly uti-
lized between autumn and spring to foster seedling growth, ensuring consistent high yields
and quality throughout the year. Consequently, due to light being the foremost influential ele-
ment impacting the growth of young tomato plants in controlled environments, further inves-
tigation is warranted.
2. Materials and methods
2.1 Experimental materials
The experiment was conducted in Shanghai from October 2022 to November 2022 in the
greenhouse of Youyou Agricultural Technology Co., Ltd. Tomato line Hakumaru was used a
plant material, having big fruit size and longer fruiting season [32].
2.2 Experimental layout
After sowing by a seeder, tomato seeds (Hakumaru) germinate in an artificial climate box with an
indoor air temperature of 22˚C and an air humidity of 90% for 72 hours and then sow them in a
240-hole tray, which is placed in an artificial climate box. The photoperiod is stetted by 12h/12h,
the temperature is 25˚C/20˚C, the humidity is 65%~75%, and the LED red-blue ratio is 7:3. When
the second leaves were fully expanded, we select plants with consistent growth and transplant
them to fill lights (Fig 1). Using grass charcoal: perlite: vermiculite = 3:1:1 (volume ratio) as the
cultivation substrate, the tidal nutrient solution irrigation mode was adopted, and the nutrient
solution was formulated with 1/2 times the tomato nutrient solution. We use the time control
switch (Shanghai Sanshi Technology Development Co., Ltd.) to accurately control the photope-
riod (day: night = 12h:12h), control the temperature 25˚C/20˚C (day/night), and the humidity is
65%~75%. The power supply equipment for the plant supplemental lighting system used in this
experiment is provided by Tianchang Fu’an Electronic Co., Ltd. The experiment was repeated by
three times, each session lasted 21 days. The experiment used a combination of different LED
lamp bead numbers to acquire 4 different light intensity treatments, which were 60 μmolm
-2
s
-1
,
150 μmolm
-2
s
-1
, 240 μmolm
-2
s
-1
, 330 μmolm
-2
s
-1
, using sun light as the comparison, and the red
and blue quality ratio of LED was set to a fixed red-blue ratio of 7:3. The four light intensity treat-
ments and sun light are represented by S1, S2, S3, S4, S5, the same below.
2.3 Measurement items and methods
2.3.1 Determination of light intensity and spectrum. Prior to the experiment, the spec-
tra of different treatments were determined by spectrometer in a darkroom 20 cm directly
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below the lamp, as shown in Fig 2 and Table 1, where the black curve is the average of the pho-
tosynthesis curve, calculated by McCree [15].
2.3.2 Determination of dry matter accumulation of tomato seedling growth indica-
tors. On the 7th, 14th and 21st days of tomato plants under fill light, 10 plants were randomly
selected for each treatment, repeated 3 times, and the plant height of tomato seedlings was
measured with a ruler with an accuracy of 0.1cm. Measure the stem diameter above the first
segment with an electronic digital caliper, which the accuracy is 0.01 mm; On the 21st day,
after rinsing the tomato plant surface substrate and gray layer with distilled water, absorbent
Fig 1. LED fill light equipment.
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Fig 2. Spectral distribution of S1-S5 under different light intensities.
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paper was used to absorb the moisture on the plant surface, and then the fresh quality of
tomato seedling leaves, stems and roots was measured by an electronic balance, which the
accuracy is 0.01g. After the tomato plants were fixed at 105˚C for 15min, dried in an electric
blower drying oven at 80˚C for 48h to a constant amount. The dry mass of each part was
weighed with an electronic balance, which the accuracy is 0.01g. At last, the DQI [12] was cal-
culated as followed:
Quality index ¼stem thickness
plant height þroot dry weight
shoot dry weight
 �total dry weight
2.3.3 Determination of chlorophyll content. Treatments were made after the 21st day,
and tomato leaves were measured by using a chlorophyll analyzer [11] from Kinkolida. Each
control group selected 10 tomato leaves. The accuracy of the chlorophyll analyzer was 0.1.
2.3.4 Determination of photosynthetic properties. Tomato seedlings are treated at dif-
ferent light intensities after 21 days, the net photosynthetic rate (Pn), stomatal conductance
(Gs), and intercellular CO
2
concentration (Ci) of tomato seedlings were measured by CIRAS-3
portable photosynthesis/fluorescence instrument of Lufthansa under different light intensity
treatment. Five plants were selected for each treatment, and three leaves were selected for each
plant for assay. The gas exchange method is described below.
The infrared radiation is absorbed by gas molecules when passing through CO
2
gas (or
water vapor), resulting in a decrease in transmitted infrared energy. The amount of absorbed
infrared energy is related to the absorption coefficient (K) of the gas, gas concentration (C),
and the thickness of the gas layer (L), following the Lambert-Beer law, which can be expressed
by the following equation:
E¼E0eKCL
E
0
represents the energy of incident infrared light, while E represents the energy transmitted
through the infrared light. According to the above formula, the concentration of CO
2
or water
vapor in the measured gas can be determined. Infrared gas analyzers can only measure the
concentrations of CO
2
and water vapor. To measure photosynthetic rate, it must be combined
with the gas pathway system. Connect the infrared analyzer with the assimilation chamber to
form an open gas circuit system, providing a stable CO
2
gas source (AIR) to the assimilation
chamber. Insert the leaf into the assimilation chamber (C) and provide appropriate illumina-
tion (PAR). After the CO
2
difference (CO
2
d) and water vapor difference (H
2
Od) between the
reference and analysis chambers stabilize, record these two differences. Accurately measure
the flow rate (F) of the assimilation chamber, and then calculate the photosynthetic rate (Pn)
and transpiration rate (E) based on the leaf area (S).
2.3.5 Statistical analysis. SPSS 22.0 was used for ANOVA and significance analysis
(P <0.05). The experimental results underwent analysis of variance (ANOVA) followed by
the Tukey test. Origin Pro 2022 was used for chart production.
Table 1. Major light parameters of treatments.
Treatment Light intensity
(μmolm
-2
s
-1
)
The wavelengths of red light and blue light (nm)
S1 60 662+452
S2 150 662+452
S3 240 662+452
S4 330 662+452
S5 Sun light Full spectrum
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3. Results
3.1 Effects of different light intensity treatments on tomato plant growth
Experiments demonstrated significant variations in the morphology of tomato seedlings under
different light intensities (Table 2 and Fig 3). The results predicted that dry weight and other
parameters of tomato seedlings were the lowest in S1 treatment. Compared with other treated
seedlings, the stem diameter was relatively largest under PPFD irradiation of 240 μmolm
-2
s
-1
,
but the optimal state doesn’t increase as PPFD increases. It is clear that PPFD of 330 μmolm
-
2
s
-1
, the stem diameter is not as large as 240 μmolm
-2
s
-1
, indicating that it is important to find
out the light intensity suitable for the growth of tomato seedlings. At the same time, it can be
seen that the light intensity is weaker, the plant height of tomato seedlings is higher, indicating
that at 60 μmolm
-2
s
-1
, because of insufficient light, the plant had the phenomenon of appren-
ticeship, which is not conducive to the growth of tomatoes. From the significant difference in
the strength index, it can be seen that tomato seedlings were the strongest under the treatment
of S3, followed by S5, which is significantly compared with other treatments.
Table 2. Effects of different light intensities on morphology of young tomato plants. Different letters in columns indicate statistically significant differences
(P <0.05).
Light treatment Root dry weight (g) Shoot dry weight (g) Total dry weight (g) Plant height
(cm)
Stem diameter
(mm)
Dixon
quality
index
S1 0.99±0.05d 0.42±0.03d 1.41±0.08d 16.60±0.99a 3.57±0.18b 3.35±0.17cd
S2 1.24±0.03b 0.75±0.02a 1.99±0.06b 13.65±0.98bc 4.10±0.14a 3.34±0.08d
S3 1.63±0.08a 0.67±0.07b 2.30±0.15a 12.84±0.55cd 4.23±0.16a 5.72±0.18a
S4 1.17±0.01bc 0.58±0.01c 1.75±0.02c 11.70±0.79d 3.75±0.18b 3.59±0.05c
S5 1.14±0.01c 0.32±0.02e 1.46±0.03d 14.51±1.04b 3.25±0.02c 5.20±0.26b
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Fig 3. Root system comparison chart of tomato seedlings.
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3.2 Effects of different light intensity treatments on chloro-phyll in leaves
of tomato plants
The amount of photosynthetic pigment absorption is first of all related to light quality. In this
experiment, we control the optimal light-to-quality ratio (R:B = 7:3) [32], according to Fig 4,
we can intuitively see the gap from the leaf color, the leaves of S1 and S5 are lighter in color,
and the tomato’s leaves in the middle three groups are darker; From Fig 5(A), it is more fully
evident that under the irradiation of PPFD (photosynthetic photon flux density) of
240 μmolm
-2
s
-1
, the chlorophyll content of tomato seedling leaves is the highest, reaching a
value of 36.67. Furthermore, the chlorophyll content does not continue to increase with the
increase of PPFD. Under the condition of S5, the chlorophyll content of tomato leaves did not
accumulate sufficiently, indicating that the LED light source used for artificial light environ-
ment control has a positive effect on promoting chlorophyll content in tomato leaves. From
Fig 5(B), We can observe that PSII in groups S1 to S4 is lower than that of S5. The reason for
the lower PSII in the first four groups is the insufficient water availability in the artificial light
environment during the experiment, which resulted in the malfunction of the moisture regula-
tion system.
3.3 Effects of different light intensity treatments on photo-synthetic
characteristics of tomato plants
From Fig 6(A), it can be seen that the net photosynthetic rate is the highest at 240 μmolm
-2
s
-1
,
followed by greenhouse natural light conditions. Similarly, as the PPFD increased from
60 μmolm
-2
s
-1
to 240 μmolm
-2
s
-1
, the net photosynthetic rate also increased, but when it
reached 330 μmolm
-2
s
-1
, the net photosynthetic rate of tomato seedlings decreased instead.
Based on Fig 6(B), it can be concluded that there was not a significant difference in transpira-
tion rate among the four artificial light environment treatments. However, compared with the
Fig 4. Tomato seedling growth comparison chart.
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greenhouse natural light seedlings, the transpiration rate was significantly higher in the artifi-
cial light environment treatments. There is a certain correlation between stomatal conductance
and intercellular CO
2
concentration in Fig 6(C) and 6(D). It can be seen that among the four
Fig 5. (a). Effects of different light intensity on chlorophyll content of tomato seedlings. (b).Effects of different light
intensity on Fv/Fm content of tomato seedlings.
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groups with different PPFD levels in the artificial light environment control, the stomatal con-
ductance was the highest and the intercellular CO
2
concentration was the lowest under the
treatment of 240 μmolm
-2
s
-1
. This indicates that more CO
2
is being used for photosynthesis
and simultaneously demonstrates that the net photosynthetic rate of the tomato seedlings is
optimal under this condition.
4. Discussion
The light source plays an important role in the growth and development of tomatoes, provid-
ing energy for tomatoes on the one hand, and regulating tomato plant morphology on the
other hand [33,34]. The architecture of plants is partially regulated by light signals received
from the environment [24]. Light serves as the energy source for photosynthetic organisms,
and the intensity of light plays a crucial role in plant growth. Under low light conditions, plant
growth and productivity are hindered due to the impact on gas exchange. Conversely, exces-
sive light intensity can have detrimental effects on the photosynthetic apparatus. A large
Fig 6. (a) Effects of different light intensities on net photosynthetic rate (Pn) tomato seedlings. (b) Effects of different light intensity on transpiration rate of
tomato seedlings. (c) Effects of different light intensity on intercellular carbon dioxide concentration in tomato seedlings. (d) Effect of different light intensity
on stomatal conductance of tomato seedlings.
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amount of research has shown that the growth and development of tomato, leaf morphology,
and accumulation of dry matter are significantly affected by light intensity [18,35–37]. This
study found that the DQI of tomatoes is at its maximum under the condition of 240 μmolm
-2
s
-
1
. The DQI does not gradually increase with the increase of PPFD. This is similar to the
research of Fan, X.-X. [11] on tomatoes. However, this study is not exactly the same as his
light saturation point, indicating that different tomato varieties have different response mecha-
nisms to light intensity, which is consistent with the research of Wang, L. W. [38]. From the
root comparison diagram in Fig 4 above, it can be found that the degree of root development
also reaches its optimum at 240 μmolm
-2
s
-1
, indicating that under this treatment, the rate of
accumulation of dry matter and equality in tomato plants accelerates, further verifying the
DQI. This is consistent with the research of Shimizu, H. [39] and others on lettuce in plant
factories.
For the chlorophyll content of tomato leaves [39], SPAD [40] reflects the degree of leaf
greenness, and then the actual nitrate content of tomatoes can be understood. Therefore, this
is how to judge whether the nitrogen content in coconut coir blocks meets the growth require-
ments of tomato plants. In this experiment, the treatment with the highest chlorophyll content
was 240 μmolm
-2
s
-1
. The chlorophyll content of 150 μmolm
-2
s
-1
and 330 μmolm
-2
s
-1
did not
differ significantly from it, but they were much higher than 60 μmolm
-2
s
-1
and natural light
(W). This indicates that the PPFD always affects the chlorophyll content of tomato leaves,
which is similar to the analysis and verification of Jiang, C. [41,42]. If the absorbed excessive
light energy by the photosynthetic apparatus cannot be dissipated quickly, it can decrease the
efficiency of photosynthesis and lead to photoinhibition and potential damage to the photo-
synthetic reaction center. For example, high light stress can easily cause photoinhibition in
photosystem I, and it also inhibits the repair of photosystem II. [42]. In Fig 6 of this experi-
ment, as the PPFD increased, the energy capture efficiency of the photosystem II reaction cen-
ter (Fv/Fm) actually decreased. This indicates that although high PPFD increases parameters
such as the dry matter and DQI of tomatoes, it also causes some damage to the cells of tomato
leaves, which is consistent with the research of Zsiros, O. [43].
Stomata play a vital role in facilitating the exchange of water and air with the external envi-
ronment. The conductance of stomata is influenced by light intensity, which enhances the pro-
ton motive force [44,45]. Additionally, the development of stomata seems to be associated with
light intensity [31]. As shown in Fig 6(C) and 6(D), with the increase of PPFD, the stomatal
conductance also increases, reaching its maximum at 240 μmolm
-2
s
-1
. This indicates that the
opening of the stomata in tomato leaves is the largest at this point. On the other hand, the con-
centration of intercellular carbon dioxide is also the lowest at this point. Therefore, the
exchange efficiency between tomato leaves under this treatment and the external environment
is optimal, resulting in higher photosynthetic efficiency. This is consistent with the research of
Gorton, H. L. [46]. As shown in Fig 6(B), after the four treatments with artificial light environ-
ment control, the transpiration rate of tomato leaves was significantly higher than that of natu-
ral light (W) in the greenhouse, which is consistent with the analysis results of Jolliet, O. [47].
It is clear in Fig 6(A) that the net photosynthetic rate of tomato plants is optimal at
240 μmolm
-2
s
-1
, and slightly higher than that in greenhouses. The current study revealed that a
photosynthetic photon flux density (PPFD) of 240 μmolm
-2
s
-1
resulted in the highest net pho-
tosynthesis (Pn). Based on these findings, we observed a similar trend between plant height,
stem diameter, stomatal frequency, and Pn activity. Additionally, a higher stomatal frequency
can facilitate CO
2
uptake, thereby sustaining a higher level of photosynthetic activity. There-
fore, we speculate that the increase in Pn associated with a PPFD of 240 μmolm
-2
s
-1
is likely
influenced by stem diameter, higher stomatal frequency, and the Dixon Quality Index.
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5. Conclusions
The results clearly demonstrate that, compared to other light treatments, from 60 to
330 μmolm
-2
s
-1
, the biomass and heath index of young plants were better. More important,
240 μmolm
-2
s
-1
induced the highest energy efficiency and activity of Pn. In the research, we
found that there was no substantial gain from a PPFD above 240 μmolm
-2
s
-1
. Therefore, this
experiment verified a conclusion that the treatment of tomato seedlings by LED light source
under the artificial light can replace the natural light in the greenhouse. Compared with the
greenhouse, this method used for tomato seedling breeding in the plant factory with artificial
lighting will greatly reduce the cost and improve the energy efficiency.
Author Contributions
Conceptualization: Jun Zou.
Formal analysis: Senmao Lin, Yuefeng Li, Xing Wen.
Funding acquisition: Bobo Yang.
Investigation: Chengcui Jin, Mingming Shi, Yifan Yang, Dezhi Jin.
Project administration: Rongguang Li.
Resources: Shaojun Yang, Xiaotao Ding.
Software: Xing Wen.
Writing – original draft: Yifeng Zheng.
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