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Article

Sufficient Light Intensity Is Required for the Drought Responses in Sweet Basil (Ocimum basilicum L.)

by
Gyeongmin Lee
and
Jongyun Kim
*
Department of Plant Biotechnology, Korea University, 145 Anam-Ro, Seongbuk-Gu, Seoul 02841, Republic of Korea
*
Author to whom correspondence should be addressed.
Agronomy 2024, 14(9), 2101; https://doi.org/10.3390/agronomy14092101
Submission received: 30 July 2024 / Revised: 12 September 2024 / Accepted: 13 September 2024 / Published: 15 September 2024
(This article belongs to the Special Issue Advancement in Controlled Environment Agriculture (CEA) Automation and Crop Management)
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Abstract

:
Various environmental factors not only affect plant growth and physiological responses individually but also interact with each other. To examine the impact of light intensity on the drought responses of sweet basil, plants were subjected to maintenance of two substrate volumetric water contents (VWC) using a sensor-based automated irrigation system under two distinct light intensities. The VWC threshold was set to either a dry (0.2 m3·m−3) or sufficiently wet condition (0.6 m3·m−3) under low (170 μmol·m−2·s−1) or high light intensities (500 μmol·m−2·s−1). The growth and physiological responses of sweet basil (Ocimum basilicum L.) were observed over 21 days in the four treatment groups, where the combination of two environmental factors was analyzed. Under high light intensity, sweet basil showed lower Fv/Fm and quantum yield of PSII, compared to that under low light intensity, regardless of drought treatment. Fourteen days after drought treatment under high light intensity, stomatal conductance and the photosynthetic rate significantly reduced. Whereas plants under low light intensity showed similar stomatal conductance and photosynthetic rates regardless of drought treatment. Assessment of shoot and root dry weights revealed that plant growth decline caused by drought was more pronounced under high light intensity than under low light intensity. Thus, sweet basil showed significant declines in growth and physiological responses owing to drought only under high light intensity; no significant changes were observed under low light intensity.

1. Introduction

Plant responses to several environmental factors are complex because each environmental factor also affects one another through their interactions. Key abiotic environmental factors, including light, temperature, water, humidity, gases (carbon dioxide and oxygen), and nutrient levels significantly influence plant growth and physiological responses. Fluctuations in these abiotic factors cause extensive losses in agricultural production worldwide [1] where inappropriate environmental conditions have negative biochemical and physiological consequences for plants.
Drought is one of the most limiting factors in crop production because moisture plays a pivotal role in plant growth by providing turgor pressure to cells. Moreover, the photosynthetic rate, which provides carbon gain for plant growth, can be reduced mainly by stomatal closure due to drought conditions [2]. To understand how plants respond to drought, several research methods have been adopted, but some of the drought simulation methods were neither practical nor descriptive. Withholding irrigation for a certain amount of time can provide different drought conditions depending on other environmental factors such as temperature, humidity, and light, thus providing inconsistent results of drought responses [3]. Although osmotic agents can effectively provide drought stress for plants in molecular biology, they have limitations in drought simulations such as non-uniform stress conditions and complexity of drought stress, due to several interactive stress conditions [4].
Over the last decade, many researchers have utilized soil moisture sensors to provide quantitative and accurate moisture conditions in the media where plants are grown. Among the soil moisture sensors, frequency domain reflectometry (FDR) sensors, which take advantage of the high dielectric constant of water molecules, are regarded as the most suitable soil moisture sensors for automated irrigation systems in greenhouse crop production [5,6]. An automated irrigation system using FDR moisture sensors can precisely control the moisture level of the plant growing substrate, thus providing quantified drought stress in plants and the best irrigation practices.
In previous drought response studies with FDR sensor-based automated irrigation, maintaining a substrate volumetric water content (VWC) of 0.3 m3·m−3 in a glass greenhouse induced drought in sweet basil, thus reducing its growth [7], whereas maintaining a VWC of 0.2 m3·m−3 did not induce a drought in Ficus pumila indoors and did not cause a detrimental effect on growth [8]. Drought stress encompasses a combination of multiple factors, such as the severity of drought, rate of imposition, and historical stress experiences [9,10]; responses to drought may show variability contingent on the specific characteristics of drought imposition [11]. Furthermore, when multiple abiotic factors act in combination, the combined influence can affect plant growth and physiology differently from when observed under individual stress conditions. Recent studies have shown that plants respond to combinations of abiotic stresses, including drought paired with heat [12,13], nutrients [14], and shading [15]. Although equivalent values are applied for accurate moisture control, drought responses can have distinct aspects depending on the light environment used as the energy source for photosynthesis.
For efficient plant production and to provide the best environmental conditions for crop growth, controlled environment agriculture (CEA) has emerged, which incorporates structures and technologies to mitigate or eliminate the potentially adverse effects of abiotic factors on plant growth and development [16]. The CEA has the potential to produce high-quality food year-round by providing an optimal growth environment and presents a sustainable approach to food production by providing resilience against climate change [17]. However, controlling the environment, even in CEA, is intricate because all environmental factors are interconnected. Therefore, it is important to comprehend not only the impacts of individual abiotic stressors on plants but also the interactions among various environmental factors.
Despite extensive research on the effects of individual environmental factors on plants, particularly at the molecular level, our understanding of the quantitative interactions between abiotic factors remains limited. In the present study, the effects of light intensity on plant drought responses were investigated. The two levels of light intensity and drought were combined to enhance the understanding of the interactions between these two environmental factors.

2. Materials and Methods

2.1. Plant Materials and Growth Conditions

The experiment was conducted at Korea University, Seoul, Republic of Korea, from 23 August to 13 September 2023. Sweet basil seeds (Ocimum basilicum L.; Asia Seed Co., Seoul, Republic of Korea) were sown in two 128-cell plug trays on a germinating substrate (Sunshine Mix#5; Sun Gro Horticulture, Agawam, MA, USA). After a three-week growth period, 120 seedlings with similar growth were selected and transplanted into round plastic pots (440 mL; 10 cm in diameter). The pots were filled with a soilless substrate (Sunshine Mix #4, Sun Gro Horticulture) mixed with a controlled-release fertilizer (Multicote 6; NPK 14-14-14, Haifa Chemicals, Haifa, Israel) at a rate of 4 g·L−1. According to the manufacturer, Multicote 6 is formulated to release nutrients over a six-month period; therefore, no additional nutrients were supplied during the three-week experimental period. The transplanted seedlings were grown in a glass greenhouse for 12 days. In total, 64 plants with similar growth stages were selected one day before the application of the treatment and moved into an indoor plant growth system. The indoor plant growth system was a multitier structure with the T5 LED fluorescence lighting tubes and fans for ventilation. During the entire experiment, the average temperature and relative humidity were 25.7 ± 0.97 °C and 64.9 ± 5.20% (mean ± SD), respectively.

2.2. Light and Drought Treatments

During the experiment, the plants were exposed to two distinct light intensities at the canopy levels: 170 μmol·m−2·s−1 (Low light intensity, L) and 500 μmol·m−2·s−1 (high light intensity, H). The low light intensity of 170 μmol·m−2·s−1 was chosen based on common indoor cultivation practices, while 500 μmol·m−2·s−1 reflects the saturation point of basil’s canopy photosynthesis [18,19]. These levels allow for meaningful comparisons of drought effects without imposing extreme light stress, aligning with standard horticultural practices. To achieve these light intensities, artificial light was supplied by a different number of T5 LED fluorescence lighting tubes (Namyung lighting, Seoul, Republic of Korea) for 16 h a day. Light intensity was determined using quantum sensors (SQ-500; Apogee Instruments, Logan, UT, USA) at a distance of 18 cm from the light source. During the experiment, the plant canopy height was maintained at 18 cm from the light source by lowering the pedestal height.
Drought treatments were implemented using an automated irrigation system with FDR soil moisture sensors. Sixteen soil moisture sensors (EC-5; Meter Group, Pullman, WA, USA) were connected to a data logger (CR1000; Campbell Scientific, Logan, UT, USA) via a multiplexer (AM 16/32B; Campbell Scientific) with a 2.5 V excitation. The data logger, linked to a relay driver (SDM-16AC/DC; Campbell Scientific), facilitated the switching of the solenoid valves to control irrigation from the program. To ensure measurement accuracy, the soil moisture sensors were calibrated to match the soilless substrate used in our experiment [VWC (v/v, m3·m−3) = 0.1352 × sensor output (mV) − 33.733, r2 = 0.9928]. Each sensor was placed diagonally from the top of the substrate to the center of each pot to target the root location. Drip irrigation was conducted by drip stakes equipped with pressure-compensated emitters (2L·h−1; Netafim, Tel Aviv, Israel). Irrigation occurred at 20-min intervals when the VWC values dropped below a set point [θ = 0.2 or 0.6 m3·m−3]. The irrigation VWC thresholds were set at 0.2 m3·m−3 (−19.5 kPa, below water buffering capacity) for drought conditions and 0.6 m3·m−3 (−0.89 kPa, easily available water) for sufficiently wet conditions, as verified for a soilless substrate [20] after acquiring the moisture release curve of the substrate using Hyprop (Meters Group, Pullman, WA, USA).

2.3. Growth Measurements and Photosynthetic Parameters

Plant height, leaf area, and shoot and root fresh and dry weights were measured as the plant growth parameters. Plants were harvested at 4, 7, 14, and 21 days after treatment (DAT). Leaf area was determined using a leaf area meter (Li-3100; Li-Cor Inc., Lincoln, NE, USA). The photosynthetic rate and stomatal conductance were measured in the uppermost fully expanded leaves using a portable photosynthesis system (CIRAS-3; PP Systems, Amesbury, MA, USA). Cuvette environments of the portable photosynthesis system were set as similar to the indoor conditions (temperature at 25 °C, RH of 65%, CO2 concentration of 410 ppm, and PPFD of 170 or 500 μmol·m−2·s−1). The maximum quantum yield (Fv/Fm) and quantum yield of PSII (ΦPSII) were measured on the uppermost fully expanded leaves using a chlorophyll fluorometer (Mini-PAM; Heinz Walz 159 GmbH, Effeltrich, Germany) after dark acclimation for 20 min. The calculation of fluorescence parameters references the article about chlorophyll fluorescence [21], with the formulas of the calculation of Fv/Fm, ΦPSII: Fv/Fm = (Fm − Fo)/Fm, and ΦPSII = (F’m − Ft)/F’m. Shoot and root dry weights were measured after drying the samples for a week at 80 °C in a dry oven.

2.4. Experimental Design and Statistical Analysis

A factorial experiment with a randomized complete block design was employed, comprising four treatments and four blocks with four plants per experimental unit (a total of 64 plants with four replicates). The experiment had a 2 × 2 factorial design with two light intensity levels and a drought factor involving two levels. Two-way analysis of variance (ANOVA) was performed using PROC MIXED in the statistical analysis software (SAS 9.4, SAS Institute, Cary, NC, USA), treating light and VWC as fixed effects and blocking as a random effect. Subsequently, pair-wise comparisons with least-square means were conducted at a significance level of α = 0.05.

3. Results

3.1. VWC Changes with the Automated Irrigation System

During the 21 days of the experiment, the substrate VWC was monitored using an automated irrigation system equipped with FDR sensors. VWC treatments at 0.6 m3·m−3 (0.6H and 0.6L) consistently maintained their threshold VWC levels throughout the experiment, regardless of light intensities (Figure 1). However, VWC treatments at 0.2 m3·m−3 (0.2H and 0.2L) decreased their VWC with different rates depending on light intensities. Irrigation was suspended until the VWC of pots reached their irrigation threshold VWC at 0.2 m3·m−3, and the first irrigation in 0.2H occurred at DAT 7, whereas that of 0.2L occurred at DAT 9, suggesting that the higher light intensity provided a faster VWC decrease than low light intensity.

3.2. Overall Growth of Sweet Basils

The overall growth of sweet basil differed depending on the light intensity and drought treatment and varied greatly depending on the timing of measurement after treatment. In the early phase after treatment (DAT 4), the change in the majority of growth parameters was mostly due to light intensity; however, the effects of drought appeared at DAT 7 (Figure 2).
Plant height was consistently affected by light intensity, with taller plants growing under high light intensity from DAT 7 onward (Figure 2A). Leaf area was greater under high light intensity at DAT 4 and became greater in well-watered plants than in plants undergoing a drought treatment starting DAT 7 (Figure 2B). Plant height at 21 d after treatment did not differ according to the interaction between light intensity and drought. However, the leaf area showed varying responses to the drought effect based on the light intensity at the final harvest. The reduction in leaf area due to drought was significant only under high light intensity, but not under low light intensity. Shoot/root fresh and dry weights were consistently higher under the high light intensity than those under low light intensity, regardless of the drought treatment throughout the entire experiment (Figure 2C–F). Drought effect was observed on the root fresh weight from DAT 4, shoot fresh weight and shoot dry weight from DAT 7, and root dry weight from DAT 14. Starting DAT 14, an interaction effect of light intensity and drought was observed on these four parameters (PL×V < 0.05), indicating that the drought effect on shoot and root growth was more pronounced under high light intensity, whereas low light intensity did not show a considerable reduction in shoot and root growth under low light conditions.

3.3. Physiological Responses

Sweet basils under low light intensity showed higher Fv/Fm and ΦPSII, which were strongly affected by light intensity but not by drought treatment (Figure 3A,B). Although there was no decrease in photosynthetic quantum yield, photosynthetic parameters, including stomatal conductance and photosynthetic rate of sweet basil, varied across treatments according to the timing of measurement (Figure 3C,D). The effect of light intensity on photosynthetic parameters, including stomatal conductance, was consistently pronounced immediately after the treatment throughout the experiment. In contrast, the effect of drought treatment was shown to affect the photosynthetic rate later from DAT 7 than on stomatal conductance, which occurred as early as DAT 4. At DAT 14, both the stomatal conductance and photosynthetic rate with 0.2 m3·m−3 treatment showed a significant decrease compared to 0.6 m3·m−3 treatment under high light intensity, but no differences under low light intensity (PL×V < 0.05). In contrast, at DAT 21, the interaction effect was significant for the photosynthetic rate (PL×V < 0.01), indicating that only drought under high light intensity reduced photosynthesis in sweet basil.

3.4. Total Irrigation Amount and Water Use Efficiency

For 21 days of the experiment, the total irrigation amount for sweet basil was greater under high light intensity than under low light intensity (PLight < 0.001), and the high VWC treatment resulted in more irrigation than the low VWC treatment (PVWC < 0.001) (Figure 4A). However, the difference in the irrigation amount between light intensities was dependent on VWC, whereas the low VWC treatment did not show a significant difference in the irrigation amount between the light intensity treatments. The total irrigation amount of 0.6 m3·m−3 was 2.8 times greater than that of 0.2 m3·m−3 under high light intensity and 1.9 times greater under low light intensity. Similarly, sweet basil grown under higher light intensity and lower VWC had higher WUE values than those grown under low light intensity and high VWC (PLight < 0.001, PVWC < 0.001) (Figure 4B). Even though the effect of drought on the total irrigation amount differed according to light intensity (PL×V < 0.001), the interaction effect of light intensity and drought on WUE was not significant, suggesting that both high light intensity and low VWC enhanced the WUE of sweet basil.

4. Discussion

The primary effects of drought on plants include diminished rates of cell division and expansion, reduced leaf size, inhibited stem elongation, restricted root proliferation, and reduced stomatal conductance [22,23,24]. A considerable number of studies have reported similar drought responses in various plants [7,10,15,25]; however, the magnitude of their responses was not consistent. In particular, plants grown indoors did not show clear drought responses [8]. Plant responses to the environment are complex because of the interactions among various environmental factors. Kim and van Iersel [9] reported that slowly imposed drought could alleviate drought stress by providing more time for plants to acclimate. Similarly, the current study revealed that different light intensity levels could provide different drought imposition rates for sweet basil; thus, different physiological responses to drought were observed. The VWC graph indicated that the water use of sweet basil under high light intensity was greater than that under low light intensity (Figure 1), thus providing a different drying imposition rate. Therefore, this result demonstrated that the imposition of drought treatment by the soil moisture sensor-based automated irrigation system was executed well across different light intensities. Even though several drought stress studies implemented drought stress either by withholding irrigation or by adjusting irrigation amounts, without proposing quantitative drought level [14,25], this study could provide quantitative drought levels by maintaining a certain VWC level using a soil moisture sensor-based automated irrigation system. Therefore, this system can provide the same substrate under drought conditions, regardless of other environmental factors, including light intensity.
As expected, sweet basil plants grown under high light intensity or well-watered conditions demonstrated greater growth from DAT 7 than those grown under low light intensity or drought conditions (Figure 2). However, the interaction effect of light intensity on sweet basil growth initially was observed both in the shoot and root, with fresh and dry weight at DAT 14. These results indicated that the effects of drought on the overall growth of sweet basil were more pronounced under high light intensity than under low light intensity. The previous research on plant drought responses in a greenhouse showed significant growth decline, maintaining 0.3 m3·m−3 compared to 0.6 m3·m−3 [7]. However, according to a similar drought study but that was conducted indoors with low light intensity [8], plants grown at 0.2 m3·m−3 and 0.6 m3·m−3 displayed a similar growth, even though their VWC differences were greater. Deng et al. [15] also reported that providing drought (30% of field capacity) with different light levels by shading (30% of sunlight) in a field and combining drought and shading reduced the photosynthetic rate and growth of the Pinus seedlings. However, their drought effect on the reduction in photosynthetic rates and growth occurred regardless of shade, and these non-significant interactions may be due to the different severities of drought and light intensities, along with different woody species. In our study, the interaction effect of light intensity on sweet basil growth was significant, suggesting that drought studies should carefully consider light intensity to provide a certain drought imposition condition, particularly indoor conditions.
For the photosynthetic parameters, high light intensity certainly provided higher photosynthetic rates of sweet basil regardless of drought from DAT 4, but the drought effect and the light intensity effect on drought were gradually revealed (Figure 3D). Sweet basil plants under high light intensity showed lower Fv/Fm (Figure 3A), but all basil plants had Fv/Fm within the optimal range around 0.8 regardless of the light intensity or drought treatment [26,27]. Similar to the Fv/Fm results, the quantum yield of PSII (ΦPSII) under high light intensity was lower than those under low light intensity regardless of drought treatments (Figure 3B). A decrease in ΦPSII under high light intensity has been repeatedly reported as plants under high light intensity have excessive quantum compared to that required [28,29]. These observations indicate that the photosynthetic capacity of photosystems is mostly dependent on light intensity, regardless of the effect of drought, which is consistent with the finding that the susceptibility of PSII activity to drought is less than that of other physiological responses [25].
Nevertheless, our results showed the obvious decline in photosynthesis owing to drought under high light intensity, mostly due to stomatal conductance (Figure 3C,D). The photosynthetic rate of sweet basil exhibited various responses to light intensity and drought, although PSII activity was primarily influenced by light intensity. Stomatal closure is regarded as a key factor contributing to the decline in photosynthesis by limiting CO2 influx, thus restricting photosynthetic carboxylation under drought conditions [2], and has been reported as one of the earliest physiological responses to drought [24]. Similarly, our results showed that drought treatment reduced stomatal conductance from the first measurement after treatment (DAT 4). At DAT 14, the stomatal conductance and photosynthetic rate of sweet basil under drought stress were lower than those under sufficiently wet conditions, but these significant differences only occurred under high light intensity (PL×V < 0.05). In other words, the interaction effect of light intensity on drought was significant, indicating that low light intensity mitigated the reduction in stomatal conductance and photosynthetic rate of sweet basil. Drought stress can lead to a reduction in photosynthesis; however, light intensity can also alter stomatal characteristics. A previous study showed that lowering stomata and stomatal pore width under low light intensity compared to high light intensity [30]; therefore, increasing CO2 uptake resistance due to stomatal pore width reduction by low light intensity could disturb photosynthesis. Interestingly, on the final harvest day, sweet basil plants under high light intensity showed decreased stomatal conductance, regardless of drought treatment, thus concurrently decreasing their photosynthetic rates. At the final harvest, sweet basil plants underwent a faster transition to the reproductive phase under high light intensity than under low light intensity, leading to decreased stomatal conductance and photosynthesis. Previous studies have reported that high light intensity shortens the flowering time of flowering species [31,32], thus changing the physiological changes differently depending on the growth phase. Nevertheless, the stomatal conductance of plants under high light intensity decreased drastically at the final harvest, and the effect of drought on photosynthetic rates was significant only under high light intensity. These results suggest that the short-term decrease in photosynthesis under drought conditions mostly occurs by restricting stomata, but the drought responses of plants under low light intensity were not significant because their photosynthetic rates were already limited by low light intensity. Therefore, drought stress research on plant species requiring high light intensity should consider the specific light intensity to understand the appropriate drought physiology. While there have been numerous studies on drought stress in indoor settings, including tissue culture, the light intensity in these growth environments was often unspecified or set relatively low, lower than 200 μmol·m−2·s−1 [33,34]. As our findings suggest, subjecting plants to drought conditions under inadequate light intensity may result in negligible drought responses. Therefore, careful consideration of light intensity should be required for the precision and applicability of drought physiology research in CEA. Furthermore, the molecular mechanisms behind the observed physiological changes could depend on how plants cope with drought stress under varying light conditions and investigating it would provide deeper insights into the interaction between environmental factors.
As discussed above, it was determined that treatment duration is a critical factor for understanding the effects of light intensity, drought, and their interaction. The effects of light on most growth and physiological parameters occurred relatively quickly (less than a week) in relation to the effects of drought and their interaction. Although the declines in stomatal conductance and root fresh weight were very rapid responses of plants under drought conditions, most of the growth and physiological responses to drought started to appear at DAT 7 (Table 1). Furthermore, an interaction effect of light intensity on drought appeared at DAT 14. Overall, light intensity was more dominant than drought in most growth and physiological responses during the early treatment period, except for stomatal conductance and root fresh weight. This indicates that high light intensity provides more energy for photosynthesis than low light intensity [35], although drought reduced stomatal conductance and limited CO2 uptake. The drought effect appeared gradually compared to light intensity effects because drought was slowly imposed for a week after treatment. These findings suggest that the response rate may differ depending on the stress duration. Therefore, it is essential to carefully consider an adequate treatment duration to fully comprehend and discuss the influence of each environmental factor and the interaction effects with multiple environmental factors.

5. Conclusions

To ascertain the impact of abiotic stress on plants, numerous studies are conducted indoors to better control the environment. However, within indoor conditions, interactions among multiple environmental factors can contribute to the variability of plant responses to abiotic stress. In the present study, the interaction effects of light intensity and drought on plants were investigated by employing a fixed light intensity setting and precise moisture control to regulate drought conditions. Our findings revealed that the drought responses, including reductions in plant growth, stomatal conductance, and photosynthetic rate, were more pronounced under high light intensity than under low light intensity. This indicates that studies utilizing artificial light sources for drought or related physiology studies should carefully consider light intensity to determine the physiological changes in plants while considering the interaction effect of environmental factors. Furthermore, the treatment duration also has important implications for these interaction effects because the imposition rate of stress is different. Overall, not only drought treatment itself but also more complex consideration of the interaction between other environmental factors and time would be required for a better understanding of drought response.

Author Contributions

Conceptualization, J.K.; Methodology, J.K.; Validation, J.K.; Formal Analysis, G.L.; Investigation, G.L.; Data Curation, G.L.; Writing—Original Draft Preparation, G.L.; Writing—Review and Editing, J.K.; Visualization, G.L.; Supervision, J.K.; Funding Acquisition, J.K. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the Korea Smart Farm R&D Foundation (KoSFarm), Korea Institute of Planning and Evaluation for Technology in Food, Agriculture, and Forestry (IPET) (421027-04), and a Korea University Grant.

Data Availability Statement

The data are available on request from the corresponding author.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Figure 1. Average substrate volumetric water content (n = 4) of Ocimum basilicum, as maintained by a soil moisture sensor-controlled automated irrigation system for three weeks. The plants were irrigated when the substrate volumetric water content dropped below the established set points of 0.2 m3·m−3 and 0.6 m3·m−3 under two different light intensities [170 μmol·m−2·s−1 (L) and 500 μmol·m−2·s−1 (H)]. Plants were irrigated for 10 s per application. Error bars indicate the standard errors (n = 4) every four days.
Figure 1. Average substrate volumetric water content (n = 4) of Ocimum basilicum, as maintained by a soil moisture sensor-controlled automated irrigation system for three weeks. The plants were irrigated when the substrate volumetric water content dropped below the established set points of 0.2 m3·m−3 and 0.6 m3·m−3 under two different light intensities [170 μmol·m−2·s−1 (L) and 500 μmol·m−2·s−1 (H)]. Plants were irrigated for 10 s per application. Error bars indicate the standard errors (n = 4) every four days.
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Figure 2. Changes in (A) plant height, (B) leaf area, (C) shoot fresh weight, (D) shoot dry weight, (E) root fresh weight, and (F) root dry weight of sweet basil plants under different light intensities [170 μmol·m−2·s−1 (L) and 500 μmol·m−2·s−1 (H)] and maintenance of different volumetric water contents (0.2 and 0.6 m3·m−3) for 21 days. Error bars indicate the standard error of the mean (n = 4). PLight, PVWC, and PL×V are the p values following two-way ANOVA with light and volumetric water content (VWC) treatments. Means followed by the same letter within the same number of days after treatment are not significantly different.
Figure 2. Changes in (A) plant height, (B) leaf area, (C) shoot fresh weight, (D) shoot dry weight, (E) root fresh weight, and (F) root dry weight of sweet basil plants under different light intensities [170 μmol·m−2·s−1 (L) and 500 μmol·m−2·s−1 (H)] and maintenance of different volumetric water contents (0.2 and 0.6 m3·m−3) for 21 days. Error bars indicate the standard error of the mean (n = 4). PLight, PVWC, and PL×V are the p values following two-way ANOVA with light and volumetric water content (VWC) treatments. Means followed by the same letter within the same number of days after treatment are not significantly different.
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Figure 3. (A) Fv/Fm, (B) quantum yield of PSII (ΦPSII), (C) stomatal conductance, and (D) photosynthetic rate of sweet basils under different light intensities [170 μmol·m−2·s−1 (L) and 500 μmol·m−2·s−1 (H)] and maintaining different volumetric water contents (0.2 and 0.6 m3·m−3) for 21 days. Error bars indicate the standard error of the mean (n = 4). PLight, PVWC, and PL×V are the p values following two-way ANOVA with light and volumetric water content (VWC) treatments. Means followed by the same letter within the same number of days after treatment are not significantly different.
Figure 3. (A) Fv/Fm, (B) quantum yield of PSII (ΦPSII), (C) stomatal conductance, and (D) photosynthetic rate of sweet basils under different light intensities [170 μmol·m−2·s−1 (L) and 500 μmol·m−2·s−1 (H)] and maintaining different volumetric water contents (0.2 and 0.6 m3·m−3) for 21 days. Error bars indicate the standard error of the mean (n = 4). PLight, PVWC, and PL×V are the p values following two-way ANOVA with light and volumetric water content (VWC) treatments. Means followed by the same letter within the same number of days after treatment are not significantly different.
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Figure 4. (A) Irrigation amount and (B) water use efficiency of sweet basils under different light intensities [170 μmol·m−2·s−1 (L) and 500 μmol·m−2·s−1 (H)] and maintaining different volumetric water contents (0.2 and 0.6 m3·m−3) for 21 days. Error bars indicate the standard error of the mean (n = 4). PLight, PVWC, and PL×V are the p values following two-way ANOVA with light and volumetric water content (VWC) treatments. Means followed by the same letter are not significantly different.
Figure 4. (A) Irrigation amount and (B) water use efficiency of sweet basils under different light intensities [170 μmol·m−2·s−1 (L) and 500 μmol·m−2·s−1 (H)] and maintaining different volumetric water contents (0.2 and 0.6 m3·m−3) for 21 days. Error bars indicate the standard error of the mean (n = 4). PLight, PVWC, and PL×V are the p values following two-way ANOVA with light and volumetric water content (VWC) treatments. Means followed by the same letter are not significantly different.
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Table 1. Comparison of the drought effect on sweet basil under low or high light intensity: no drought effect; ○ drought effect regardless of light intensity; ● drought effect was more pronounced under high light intensity than under low light intensity.
Table 1. Comparison of the drought effect on sweet basil under low or high light intensity: no drought effect; ○ drought effect regardless of light intensity; ● drought effect was more pronounced under high light intensity than under low light intensity.
ParametersDAT 4DAT 7DAT 14DAT 21
Plant height– ○ – ○
Leaf area– ○ ○ ●
Shoot fresh weight– ○ ●●
Shoot dry weight– ○ ●●
Root fresh weight ○ ●●●
Root dry weight––●●
Stomatal conductance ○ ○ ●–
Photosynthetic rate––●●
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Lee, G.; Kim, J. Sufficient Light Intensity Is Required for the Drought Responses in Sweet Basil (Ocimum basilicum L.). Agronomy 2024, 14, 2101. https://doi.org/10.3390/agronomy14092101

AMA Style

Lee G, Kim J. Sufficient Light Intensity Is Required for the Drought Responses in Sweet Basil (Ocimum basilicum L.). Agronomy. 2024; 14(9):2101. https://doi.org/10.3390/agronomy14092101

Chicago/Turabian Style

Lee, Gyeongmin, and Jongyun Kim. 2024. "Sufficient Light Intensity Is Required for the Drought Responses in Sweet Basil (Ocimum basilicum L.)" Agronomy 14, no. 9: 2101. https://doi.org/10.3390/agronomy14092101

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