Life Sciences in Space Research 22 (2019) 68–75

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Life Sciences in Space Research

journal homepage: www.elsevier.com/locate/lssr

Evaluation of the growth, photosynthetic characteristics, antioxidant T

capacity, biomass yield and quality of tomato using aeroponics, hydroponics
and porous tube-vermiculite systems in bio-regenerative life support systems
⁎ ⁎
Wang Minjuana,c, Dong Chenb,c, , Gao Wanlina,c,
a
Key Laboratory of Agricultural Informatization Standardization, Ministry of Agriculture, China Agricultural University, Beijing, 100083, China
b
School of Sport Social Science, Shandong Sport University, 250102, Jinan, China
c
College of Information and Electrical Engineering, China Agricultural University, 100083, Beijing, China

A R T I C LE I N FO A B S T R A C T

Keywords: The nutrient delivery system is one of the most important hardware components in tomato (Lycopersicon es-
Controlled environments culentum Mill.) production in Bio-regenerative Life Support Systems (BLSS) for future long-term space mission.
Aeroponics The objective of this study was to investigate the influences of different nutrient delivery systems (aeroponics,
Hydroponics hydroponics and porous tube-vermiculite) on the growth, photosynthetic characteristics, antioxidant capacity,
Vermiculite
biomass yield and quality of tomato during its life cycle. The results showed that the dry weight of aeroponics
Tomato
and porous tube-vermiculite treatment group was 1.95 and 1.93 g/fruit, but the value of hydroponics treatment
group was only 1.56 g/fruit. Both tomato photosynthesis and stomatal conductance maximized at the devel-
opment stage and then decreased later in senescent leaves. At the initial stage and the development stage, POD
activities in the aeroponics treatment were higher than other two treatments, reached 3.6 U/mg prot and 4.6 U/
mg prot, respectively. The fresh yield 431.3 g/plant of hydroponics treatment group was lower. At the same
time, there were no significant differences among nutrient delivery systems in the per fruit fresh mass, which was
14.2–17.5 g/fruit.

1. Introduction composition during winter is also similar to a crewed spacecraft. The

winter period, with duration of 9 to 10 months, is foreseen for the
Sustained human presence in space requires the development of validation of the systems. The long-duration of the test campaign allows
plant-based bio-regenerative life support systems (BLSS) (Fu et al., several cultivation cycles of plants and therefore several possibilities for
2016; Wheeler et al., 1996). When fully integrated into crewed habitats testing various system settings and operational modes (Santos et al.,
these systems decrease resupply requirements by (re-) generating 2016). The research initiative focuses on BLSS, especially greenhouse
human resources through biological processes (Tikhomirov et al., modules, and how these technologies can be integrated in future
2003).Within a BLSS, higher plants take a central role as they provide human-made space habitats.
food, CO2 reduction, O2 production, water recycling and waste man- Provision of water and nutrients in the amount necessary for op-
agement (Nelson et al., 1994; Salisbury et al., 1997). It has also been timal plant growth over all plant development stages is critical in BLSS
suggested through both anecdotal and scientific means that plants can (Chen et al., 2018; Gitelson and Lisovsky, 2014). The method of de-
also positively influence crew psychological well-being (Wu and livery of the nutrient/water mix (hydroponic solution) can be con-
Wang, 2015). These aspects play a key role for future space crews, who ducted in various ways. These include soilless based, nutrient media
may spend a significant part of their life away from Earth based hydroponics systems as well as systems requiring no substrate,
(Gitelson et al., 1976). such as aeroponics. Each configuration can provide certain advantages,
In order to simulate space-relevant BLSS, systems are often deployed but for space-based BLSS, aeroponics can provide the benefit that no
at Antarctic research stations because of the associated logistical, in- soil or substrate is required (minimizing waste) while potentially pro-
frastructural and environmental challenges that are analogous to ducing higher plant yields.
spaceflight applications (Bamsey et al., 2014). The crew size and The basic principle of aeroponic systems is to grow plants suspended

⁎
Corresponding authors.
E-mail addresses: wenjian_dongchen@163.com (C. Dong), wanlin_cau@163.com (W. Gao).

https://doi.org/10.1016/j.lssr.2019.07.008
Received 2 January 2019; Received in revised form 26 May 2019; Accepted 14 July 2019
2214-5524/ © 2019 The Committee on Space Research (COSPAR). Published by Elsevier Ltd. All rights reserved.
M. Wang, et al. Life Sciences in Space Research 22 (2019) 68–75

in a closed or semi-closed environment by spraying the plant's dangling

roots with a nutrient-rich, highly aerated fertigation solution.
Aeroponic equipment involves the use of sprayers, misters, foggers, or
other devices to create a fine mist of solution to deliver nutrients to
plant roots. No soil or grow media is needed for the whole life cycle.
Furthermore, the plant's nutrient uptake can be improved by the exact
control of plant root environment (Kratsch et al., 2006). Through this
innovative irrigation principle a general reduction in nutrient solution
throughput, decreased of water use, higher plant density (than tradi-
tional grow procedures), reduction in root borne disease/disease
transmission, and potentially higher plants yields can be achieved. On
the contrary, aeroponics contributes to quicker expansion of the root
system's disease of all plants. That is why individual vessels are used
containing soil for each plant in some greenhouse technologies. That
method decreases the risk of quick spreading of root system diseases
among other plants.
However, utilization capacity of the soilless system in BLSS has not
yet expanded at all on the Antarctic stations and long-duration space-
flight scale due to higher capital investment. Any system failure in BLSS
could result in a catastrophic event culminating with mission abort or,
even worse, loss of crew. It is necessary to investigate the different
soilless system availability effects on the space agricultural production
and evaluate different consequences caused by the soilless system dis-
turbance controlled environments.
Tomato (Lycopersicon esculentum Mill.), as one of the key candidate
crops for BLSS, has been widely investigated for long-term space mis-
sions. Therefore, we cultivated tomato (Lycopersicon esculentum Mill.)
plants in aeroponics, hydroponics and porous tube-vermiculite systems
and investigated the influences of different systems on the tomato
growth, photosynthetic characteristics, antioxidant capacity, biomass
yield and quality during their life cycle.

2. Materials and methods

2.1. Plant material and cultivation conditions

All of the combined light-emitting diodes (LEDs) had the uniform

spectra of red and white, and were designed by Beihang University,
China (Dong et al., 2015). The spectral distribution of the red (peak at
658 nm) and white (from 350 nm to 750 nm) light (300 W) were mea-
sured using a spectroradiometer (Avaspec-2048–UA, Avantes B.V.,
Netherlands) (Dong et al., 2014). Tomato (Lycopersicon esculentum Mill.
cv. ‘Dwarf’) plants were grown in a controlled environment cabinet
under a LED light intensity of 250 μmol m–2 s–1 at the top of the plants
containing the fruit. The tomato planting density was 5 plants per
m2.The temperature ranged from 25 ± 3 °C during the light period
(14 h) to 18 ± 3 °C in the dark (10 h), and the relative humidity was
70 ± 10%. The temperature was controlled using cool air following
into cabinet from central cooler. The CO2 level was the same as that of
atmosphere outside. The modified Hoagland nutrient solution was the
basic culture medium (Table 1).
Fig. 1. Different characteristics of the nutrient delivery systems. (a) Aeroponics
Table 1 system. (b) Hydroponics system. (c) Porous tube-vermiculite system. For the
Nutrient compositions. porous tube-vermiculite system, plants were planted in pots containing only
vermiculite.
Compositions Concentration (mg/L)

Ca(NO3)2•4H2O 945 2.2. Culture systems

KNO3 607
NH4H2PO4 115
MgSO4•7H2O 493
To investigate the influence of different culture methods on the
FeEDTA 28 tomato plants during ontogenesis, experiments were divided into 3
H3BO3 2.86 groups according to different systems: aeroponics, hydroponics and
MnSO4•4H2O 2.13 porous tube-vermiculite systems (Fig. 1). The three systems constructed
ZnSO4•7H2O 0.22
primarily of relatively inert materials such as glass, Teflon and stainless
CuSO4•5H2O 0.08
(NH4)6Mo7O24•4H2O 0.02 steel were used for growth of tomato plants. Each plant growing area
pH 5.8–6.3 was 1 m2.

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An aeroponics system was designed by China Agricultural Na2HPO4eNaH2PO4 buffer solution (pH = 7.0) and 0.1 M H2O2. The
University. The aeroponic tubing and misters are designed so that they optical density was determined every 1 min at λ = 240 nm.
can be easily installed within the top of the growth trays. The archi-
tecture includes pairs of misters spaced at 20 cm intervals. The misters 2.4.3. Malonaldehyde (MDA) content
are angled downwards to ensure good coverage of the plants roots over Determination of MDA followed the method of Stewart and Bewley
the entire growth cycle of the respective crops. The tubing and misters (1980). Briefly, 10 mL 0.1% trichloroacetic acid (TCA) pestled homo-
are easily installed within the top of the plant channels during the genate was used to centrifuge wheat leaves (0.5 g) at 4000 rpm for
preparation of each growing cycle. Excess aeroponic water is collected 10 min. 2 mL supernatant was added to 4 mL 5% thiobarbituric acid
in the bottom of the slightly angled channels and flows out drainage (TBA) which was made up by 20% TCA. The mixture was heated at
tubes back to the respective petal reservoir. The solution is analyzed 95 °C for 30 min and then cooled in ice-bath rapidly. The supernatant
(e.g. ion-selective, EC and pH sensors) and composition adjustments are was obtained by centrifuging at 3000 rpm for 10 min. The absorbency
then made accordingly. of the supernatant was recorded at 532 nm. The value for non-specific
An hydroponics system was used with the modified Hoagland nu- absorption at 600 nm was subtracted. The MDA content was calculated
trient solution as listed in Table 1. The nutrient solution was poured using its extinction coefficient of 155 mM−1 cm−1.
into the cultivating plate that was covered by cystosepiments where
there were some holes for plant cultivation. 2.5. Biomass yield analyses
An porous tube-vermiculite system was designed and specific details
on chamber design and control have been described previously (Chen 2.5.1. Lycopene & β-carotene
et al., 2014; Dong et al., 2015). Plants were grown in vermiculite, Lycopene and β-carotene (mg/100 mL) were evaluated as outlined
continuously maintained under optimal irrigation, and supplied with by Nagata and Yamashita (1992). One gram of tomato sample was
1X strength Hoagland solution every 3 days. taken in a test tube; poured acetone: hexane (4:6) in the test tube and
The tomato seeds were germinated in the equipment at 24 °C air then the mixture was homogenized. The optical density of the homo-
temperature for 10 days and the tomato seedlings were transplanted to genized mixture was measured at 663, 645, 505 and 453 nm. The va-
different systems. According to the growth characteristics of tomato lues of lycopene and β-carotene were calculated by following formula:
plants, the tomato life cycle was divided into four stages: Initial stage
(0–30 days), Mid-stage (30–60 days), Development stage (60–90 days) Lycopene(mg/100 mL) = −0.0458A 663+0.204A 645+0.372A505
and Late stage (90–120 days). Fruit were harvested every week after − 0.0806A 453
100 days after transplanting. Early yield, fruit number and single fruit β−carotene(mg/100 mL)=0.216A 663 − 1.22A 645 − 0.304A505+0.452A 453
mass were calculated from fruits in the first three harvests.
where: A is the absorbance at 663, 645, 505 and 453 nm.
2.3. Photosynthetic characteristics analyses
2.5.2. Edible and inedible biomass
2.3.1. Chlorophyll contents Fruit weight (g), total yield (g/plant) and different part weight were
At the initial stage, mid-stage, development stage and late stage, recorded according to Chen et al. (2014) and Meyer et al. (1999).
chlorophyll was extracted from the leaves (fully expanded, exposed) of
plants at a similar position within each treatment. Leaves were weighed 2.6. Data statistics
out in 0.1 g (fresh weight, W), and samples were ground in a mortar.
The optical density was measured with a UV-1200 spectrophotometer The experiment was setup in a completely randomized design. All
(SP-75, Shanghai spectrum instruments co., LTD, China) at 663 nm experiments were performed in triplicate. The average value of total 6
(OD663) for chlorophyll a (Chl. a), and 645 nm (OD645) for chlorophyll b measurements ± standard deviation was regarded as the final result.
(Chl. b) (Li et al., 2013; Lichtenthaler and Wellburn, 1983). Leaf sam- All statistical analyses were performed using SPSS 18.0. P values less
ples were frozen in liquid nitrogen and stored at −80 °C until mea- than 0.05 were considered statistically significant.
sured.
3. Results
2.3.2. Photosynthetic efficiency
Portable photosynthesis instrument (Li-6400XT, Li-Cor, USA) was 3.1. The response of photosynthetic characteristics to different treatments
used for the determination of photosynthetic characteristics. Leaf gas-
exchange parameters included photosynthetic rate (A), stomatal con- Different nutrient delivery systems had significant effects on the
ductance (gs) and intercellular CO2 concentration (Ci) using the second growth and development of the tomato plants. From Fig. 2a, chlor-
leaf at the tomato terminal bud. Water use efficiencies (A/gs) were ophyll a concentrations fluctuated during the whole life cycle. Both of
calculated by dividing A by gs and the instantaneous carboxylation the aeroponics and porous tube-vermiculite system had the high ad-
efficiencies (A/Ci) were also calculated (Dong et al., 2015). vantages from initial stage mg/g to late stage and the hydroponics
system group had a lower level at both mid-stage 1.56 mg/g and de-
2.4. Antioxidant capacity analyses velopment stage 1.62 mg/g. About the chlorophyll b, only the devel-
opment stage was the sensitive stage for different nutrient delivery
2.4.1. Peroxidase (POD) activity systems, with aeroponic, hydroponic and porous tube-vermiculite
POD activity was analyzed spectrophotometrically at 470 nm using having values of 0.79 mg/g, 0.59 mg/g and 0.78 mg/g, respectively
guaiacol as a phenolic substrate with hydrogen peroxide (Diaz et al., (Fig. 2b). The value added of chlorophyll b was greater than that of
2001). The reaction mixture contained 0.15 mL of 4% (v/v) guaiacol, chlorophyll a for both of the aeroponics and porous tube-vermiculite
0.15 mL of 1% (v/v) H2O2, 2.66 mL of 0.1 M phosphate buffer systems, especially at the development stage; thus the chlorophyll a/b
(pH = 7.0) and 40 μL of enzyme extract. Blank sample contained the decreased (Fig. 2c). Aeroponics system and porous tube-vermiculite
same mixture without enzyme extract. system had a significant higher value than that for the hydroponics
system. The value added of chlorophyll b was greater than that of
2.4.2. Catalase (CAT) activity chlorophyll a for both of the aeroponics and porous tube-vermiculite
CAT activity was determined according to the method described by systems, especially at the development stage. And thus the chlorophyll
Kumar and Knowles (1993). CAT reaction solution consisted of 100 mM a/b decreased (Fig. 2c). Throughout the senescence period, particularly

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transpiration rate of tomato leaves were increased at the mid-stage and

reached the top level at the development stage (Fig. 3c), reflecting an
imbalance between water uptake and transpiration rate, especially in
hydroponics system treatment. In particular, the increase in A at the
development stage, was smaller than the increase in gs, so A/gs de-
creased (Fig. 3d), allowing the tomato plants to more efficiently use
water for the high yield in finally.

3.2. The responses of antioxidant system to different treatments

We also studied the activity of the antioxidant enzymes POD and

CAT and the production of MDA in tomato leaves during ontogenesis.
POD and CAT activities increased during early leaf development,
reaching their maximal levels at the development stage and decreasing
later in senescent leaves. Also, these antioxidant enzymatic activities
were at low level in the plants grown under porous tube-vermiculite
condition throughout leaf development (Fig. 4a and b). At the initial
stage and the development stage, POD activities in the aeroponics
treatment were higher than other two treatments, reached 3.6 U/mg
prot and 4.6 U/mg prot, respectively. As shown in Fig. 4c, MDA pro-
duction increased with leaf growth and development, especially at the
mid-stage and the development stage, suggesting that these two stages
may be more important role in regulating leaf senescence in tomato
plants by increasing reactive oxygen species (ROS) production. Alter-
natively, lower ROS production may decrease the incidence of oxidative
stress, translating as a reduced stimulus for antioxidant production.
Such reduced oxidative pressure would also correspond well with a
smaller POD activity. The lycopene (mg/100 g) values were recorded
from different tomato plants under aeroponics, hydroponics and porous
tube-vermiculite systems and range from 4.57 to 5.01 mg/100 g re-
spectively (Fig. 5).

3.3. The responses of biomass yield to different treatments

In this experiment, there was no difference in fruit yield per plant

and fresh mass per fruit between aeroponics and porous tube-vermi-
culite grown plants (Fig. 6a). However, the yield of hydroponics
treatment group was significantly lower than others. The fresh weight
reached only 431.3 g/plant. At the same time, there were no significant
differences among nutrient delivery systems in the per fruit fresh mass
(Fig. 6b), which was 14.2–17.5 g/fruit. The plant yield depends on the
weight and number of fruit. The number of tomato fruit was lower in
the hydroponics treatment group. Therefore, the fruit weight was di-
rectly proportional to the yield of a plant. More importantly, the dry
weight of the hydroponics treatment group had the significant differ-
ence from other groups (Fig. 6c). The dry weight of aeroponics and
porous tube-vermiculite treatment group was 1.95 and 1.93 g/fruit, but
the value of hydroponics treatment group was only 1.56 g/fruit. In
addition, the dry weight of the tomato plants in different parts was also
the same result, which means the tomato plants in hydroponics treat-
ment may not so thick and strong compared with aeroponics and
porous tube-vermiculite treatments (Fig. 6d).

Fig. 2. Response of chlorophyll a (a) and chlorophyll b (b) and chlorophyll ratio 4. Discussion
(c) of tomato leaves at different stages of ontogenesis to different treatments.
Vertical bars are means ± SD. Within each graph, bars labeled with lowercase
Stimulation of photosynthesis is the driving force for increased
letters are significantly different at p ≤ 0.05.
growth and yield of tomato in aeroponics and porous tube-vermiculite
groups. Over prolonged periods of exposure to different nutrient de-
at the late stage, there was no significant difference either chlorophyll a livery systems (days to weeks), the stimulation of photosynthesis and
or b contents from the tomato leaves. some physiology index gradually diminished. Senescence typically in-
Tomato plants sense and respond to different nutrient delivery volves cessation of photosynthesis and degeneration of cellular struc-
systems through modified photosynthesis (A) and stomatal conductance tures, with strong losses of chlorophyll (Ougham et al., 2010). How-
(gs) (Fig. 3a and b). Both A and gs maximized at the development stage ever, at the mid-stage and development stage, the effect of nutrient
and then decreased later in senescent leaves. At the development stage, delivery systems became more significant to some extent, which may be
A of the tomato plants under porous tube-vermiculite treatment because the stages from vegetative growth to reproductive growth are
reached 16.4 μmol CO2 m−2 s−1. For the transpiration rate, the more sensitive. The water and the ion concentration played more

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Fig. 3. Response of photosynthetic rate (a), stomatal conductance (b), transpiration rate (c) and water use efficiency (d) of tomato leaves at different stages of
ontogenesis to different treatments. Vertical bars are means ± SD. Within each graph, bars labeled with lowercase letters are significantly different at p ≤ 0.05.

important roles in the plant growth, which led to the photosynthesis fruits (Baranska et al., 2006). In tomatoes, the content of β-carotene has
better or not. Hydroponics, managed as a closed system, enables nu- been shown to increase as the fruit ripens. Since β-carotene accumu-
trient to be well controlled, which is necessary in order to avoid hyper- lation is a ripening-related event in tomato and its formation from ly-
accumulation and the consequent toxic effects. It can also be used for copene appears to be principally under transcription regulation (Fraser
improving the quality and the shelf-life of fruit with adequate nutrient et al., 2007; Lee et al., 2012).
concentrations for the human diet. Nutrient sensing is an intrinsic BLSS production of tomato and other solanaceous vegetables is
property of guard cells, which are thought to respond to the inter- significantly hindered by attacks of soil-borne diseases and sudden
cellular carbon dioxide concentration (Ci) rather than CO2 concentra- temperature fluctuation under the open field conditions. To cope with
tion at the leaf surface. Ion and organic solute concentrations mediate these challenges, the soil-less technique is considered a promising tool
the turgor pressure in the guard cells that determines stomatal aperture. for space vegetable productions. Hydroponics is the most intensive
Stomata closure implies lower CO2 availability, and ultimately lower method for crop production in the agricultural industry. This enables
CO2 fixation by Rubisco, which may finally result in lower biomass the plants to achieve higher growth of the shoot system with more
production (Leakey et al., 2009). vegetation, larger fruits, flowers and other edible parts. Plants in hy-
Greater Ci may translate into greater CO2/O2 ratio in the chlor- droponics grow up to two times faster with higher yields than with
oplast, causing lower oxygenation rates by Rubisco and therefore lower conventional soil farming methods due to higher oxygen levels around
rates of photorespiration and associated ROS production in tomato the root system, optimum pH along with increased nutrient and water
cultivar. However, the mechanism needs to be further investigated. uptake (Ghazvini et al., 2007). The hydroponic culture of tomato and
Moreover, responses of plant organs to environmental factors should be other susceptible vegetable crops can facilitate their successful and
different among different growth stages. Plants have adaptability to space production. Therefore, a precise detection and management of
environmental changes. biotic and abiotic stresses should be taken into consideration for in-
The lycopene content showed red colored tomato (Baranska et al., creased production.
2006), and the degree of redness is directly proportional to the con- The incorporation of aeroponics, as described, presents several ad-
centration of lycopene, while orange or yellow color shows less con- vantages over other hydroponic nutrient delivery system options, in
centration of lycopene. The lycopene content of tomato plants grown in particular for missions to the lunar surface where transporting growth
the aeroponics and porous tube-vermiculite systems was higher than substrate can itself present challenges from a mass and waste perspec-
the other group. But the tomato β-carotene content was no significant tive. That said, aeroponics is a technology that although discussed
difference among different treatments. The results are in the range of within the hydroponics literature for some time remains one that re-
the findings of recorded 0.23–4.00 mg/100 g of β-carotene in tomato quires further investigation (Clawson et al., 2000; Weathers and Zobel,

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Fig. 5. Response of Lycopene and β-carotene content of tomato plants to dif-

ferent treatments. Vertical bars are means ± SD. Within each graph, bars la-
beled with lowercase letters are significantly different at p ≤ 0.05.

fertilizer nutrients) (Jones and Jones, 1997). If any given nutrient is

deficient, plant growth can be negatively influenced. Similar effects can
arise when given nutrients are present in excessive concentrations, ei-
ther by direct toxic effects or more likely, by limiting the uptake of
other nutrient ions. In addition to sensor technology, further work is
required in the development of the control system that could subse-
quently control nutrient salt additions to result in the optimum solution
of interest (Bamsey et al., 2012). This is inherently challenging because
the operator cannot simply add one nutrient ion of interest (e.g. K+) but
instead they must also add the other components contained within the
employed salt (e.g. NO3− from KNO3). Thus when attempting to adjust
the concentration of a given ion, other ions may go out of balance
without appropriate control or without the forethought to carry addi-
tional nutrient salts options that may otherwise not have been carried.
Further developments surrounding the logic behind such hydroponic
solution management choices must also be advanced.
Although literature exists suggesting the benefits of aeroponics nu-
trient delivery systems, little experimental evidence exists that de-
monstrates these benefits in a quantitative manner. Controlled experi-
ments will be conducted to assess these possible yield benefits.
Experimental utilization and documentation of the benefit and opera-
tional utilization of ion-selective sensors and various UV disinfection
systems will also be conducted. Consideration of the use of aeroponics,
ion-selective sensors and disinfection systems in the Antarctic as well as
space-based systems will also be performed.
Keeping in view the importance of tomato and need of Chinese
Antarctic Great Wall Station, Antarctic Zhongshan Station and Kunlun
Station, it was imperative to carry out an experiment on tomatoes under
greenhouse conditions by using different nutrient delivery systems in
Fig. 4. Response of POD activity (a), CAT activity (b) and MDA content (c) of China. The research evaluation was based on tomato morphological,
tomato leaves at different stages of ontogenesis to different treatments. Vertical qualitative and analytical parameters, which are imperative for the
bars are means ± SD. Within each graph, bars labeled with lowercase letters development of rapid screening techniques and proper selection
are significantly different at p ≤ 0.05. method of different nutrient delivery systems. In addition, the project
will further enhance the knowledge about crew time assessments. The
1992). In particular, production improvements (if any) of aeroponics quantification of realistic crew time requirements over the long-term
need to be more systematically assessed as well as such things as ap- operation of this greenhouse within this mission relevant environment
propriate misting frequency and clogging and cleaning requirements for will have considerable benefit over laboratory extrapolations. In addi-
a true confirmation of the utility of aeroponics (in particular in a hybrid tion to providing a plant production facility that will benefit the sta-
aeroponics-other implementation) to be better known with certainty. tion's long duration crews, the project strives to advance the technology
It is well established that there are anywhere from 15 to 18 essential readiness of a number of technologies that could be applied to on orbit
plant nutrients that govern plant growth, development and reproduc- and planetary surface plant production systems.
tion (of which oxygen, carbon and hydrogen can be considered non- In these years, BLSS experiments are developed quickly in all over
the world. One of the most recent developments in BLSS has been the

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Fig. 6. Response of yield (a), fruit fresh mass (b), fruit dry mass (c) and different part dry weight (d) of tomato plants to different treatments. Vertical bars are
means ± SD. Within each graph, bars labeled with lowercase letters are significantly different at p ≤ 0.05.

establishment and testing of the Chinese Lunar Palace 1 (LP1). LP1 is a treatment group was lower. Fully understanding how the biochemical
highly closed ecosystem integrating efficient higher plant cultivation, mechanisms are directly or indirectly affected by water and nutrients in
animal protein production, urine nitrogen recycling, and bioconversion fruit tissues at ripening should help considerably in optimizing the
of solid waste (Fu et al., 2016). Introducing crops into the life support treatment procedures and protocols. These findings are useful for de-
system to provide food and O2 is appealing for long-term space mission. signing and operating growth technologies for enhanced tomato pro-
To date, dozens of crop species have been tested for the application in duction.
the BLSS. Each of them has its own advantages. Furthermore, different Research in this area should continue as in addition to enhancing
crops may have different suitable nutrient delivery systems. This paper our understanding of fundamental plant biology it will continue to
is provided a method and the selection process of tomato nutrient de- enhance tomato yields and overall system reliability. This improved
livery systems. Through the selection of specific nutrient delivery sys- knowledge of plant nutrition will further the ability of the lunar base
tems, we hope to identify some cultivars that are easier to adapt to the operators to also garner scientific data related to the influence of the
controlled environment conditions and can keep higher productivity. reduced gravity environment of the lunar surface on crop growth.

5. Conclusions Conflict of interest

In our results, the dry weight of aeroponics and porous tube-ver- None.
miculite treatment group was 1.95 and 1.93 g/fruit, but the value of
hydroponics treatment group was only 1.56 g/fruit. Nutrient delivery is
the provision of water and nutrients in the amount necessary for op- Acknowledgements
timal tomato growth over all plant development stages. Both tomato
photosynthesis and stomatal conductance maximized at the develop- The authors would like to thank their colleagues for their support of
ment stage and then decreased later in senescent leaves. Stimulation of this work. The detailed comments from the anonymous reviewers were
photosynthesis is the driving force for increased growth and yield of gratefully acknowledged. This work was supported by the China
tomato in all groups, but the aeroponics and porous tube-vermiculite Postdoctoral Science Foundation (2018M63022) and Shandong Social
treatments are stronger, those may be due to the salt accumulation Science Planning Fund Program(18CQXJ33). We also thank Mark
lower. There was no difference in fruit yield per plant between aero- Nelson for manuscript review and helpful comments.
ponics and porous tube-vermiculite grown plants, but the hydroponics

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