Evaluating Water Use Dynamics and Yield Responses in Capsicum chinense Cultivars Using Integrated Sensor-Based Irrigation System

Abstract

Efficient irrigation management is essential for optimizing yield and quality in specialty crops like hot peppers (Capsicum chinense), particularly under controlled greenhouse environments. This study employed a novel sensor-based system integrating soil moisture and sap flux monitoring to evaluate water use dynamics in Capsicum chinense, a species for which such applications have not been widely reported. Three cultivars—Habanero, Helios, and Lantern—were grown under three volumetric soil moisture contents: low (15%), medium (18%), and high (21%). Water uptake was measured at leaf (transpiration, stomatal conductance) and plant levels (sap flux via heat balance sensors). Photosynthesis, fruit yield, and capsaicinoid concentrations were assessed. Compared to high irrigation, medium and low irrigation increased photosynthesis by 16.6% and 22.2%, respectively, whereas high irrigation favored greater sap flux and vegetative growth. Helios exhibited an approximately 8.5% higher sap flux as compared to Habanero and about 10% higher as compared to Lantern. Helios produced over 30% higher fruits than Habanero and Lantern under high irrigation. Habanero recorded the highest pungency, with a capsaicinoid level of 187,292 SHU—exceeding Lantern and Helios by 56% and 76%, respectively. Similarly, nordihydrocapsaicin and dihydrocapsaicin accumulation were more cultivar-dependent than irrigation-dependent. No significant interaction between cultivar and irrigation was observed, indicating genotype-driven water use strategies. Our study contributes to precision horticulture by integrating soil moisture and sap flux sensors to reveal cultivar-specific water use strategies in Capsicum chinense, thereby demonstrating the potential of an integrated sensor-based irrigation system for efficient irrigation management under increasing water scarcity in protected environments. As a preliminary greenhouse study aimed at maintaining consistent irrigation throughout the growing season across three volumetric soil moisture levels, these findings provide a foundation for subsequent validation and exploration under diverse soil moisture conditions including variations in stress duration, stress frequency, and stress application at different phenological stages.

1. Introduction

Hot peppers (Capsicum chinense) are globally valued for their unique pungency, vibrant nutritional profile, and economic significance across culinary, pharmaceutical, and cosmetic industries [1,2]. Beyond their culinary appeal, hot peppers are rich sources of bioactive compounds, vitamins, and antioxidants, positioning them as a vital component of healthy diets worldwide [3,4,5,6,7,8]. Capsicum chinense peppers, renowned for their intense pungency and rich phytochemical profiles, are gaining substantial economic importance globally. In 2020, global chili pepper production was estimated at approximately 40 million tons [9], and the demand for high-capsaicinoid cultivars such as C. chinense continues to grow, driven by their wide-ranging applications in the food, pharmaceutical, and nutraceutical sectors. Capsaicin (the principal pungent compound) has also been widely studied for its pharmacological properties, including antibacterial, antioxidant, and anti-inflammatory activity [10,11]. As a result, the global market consumption of chili peppers is expected to reach USD 7325.67 million by 2028, growing at a CAGR of 8.58% [12]. This rising demand has led to the expanded cultivation of C. chinense in new agro-climatic zones, producing novel chemotypes with distinct aroma profiles and varying heat levels [13]. With increasing consumer interest in functional foods and natural health products, C. chinense cultivars with elevated capsaicinoid content are emerging as high-value crops in global horticultural markets. Increasing consumer demand for hot peppers highlights the importance of optimizing their production systems for sustainable high-quality yield [1,2].

Greenhouse cultivation offers a promising alternative to field production for hot peppers, particularly in addressing the challenges posed by abiotic stresses such as drought and temperature extremes [14]. Compared to open-field systems, greenhouse environments allow for greater control over key factors such as water availability and temperature. Studies have shown that greenhouse-grown peppers can achieve up to tenfold higher yields and improved fruit quality compared to field-grown counterparts [14,15]. Successful production models in Spain and Florida have further demonstrated the scalability and profitability of greenhouse-based pepper cultivation [15,16,17], positioning it as a cornerstone for sustainable intensification.

Water stress remains one of the most critical limitations to hot pepper production, especially under adverse weather conditions. Due to their shallow root systems and high sensitivity to soil moisture deficits, hot peppers are particularly vulnerable to drought conditions. Water stress severely impacts physiological processes such as photosynthesis, stomatal conductance, and transpiration rates in hot peppers [18,19,20,21], leading to substantial reductions in biomass accumulation, flower and fruit set, and overall yield [22]. A 21% reduction in photosynthesis rate and a 4–11% reduction in stomatal conductance were observed under severe water stress in pepper plants [20]. Similarly, Molla et al. [21] observed a reduction of 20–24% in photosynthesis rate, 20–37% in transpiration rate and 32–44% in stomatal conductance rate as compared to control under 100% field capacity. In the Capsicum species, yield losses of up to 30% under drought conditions have been reported as compared to well-watered plants at 80–85% water holding capacity [22]. Importantly, drought stress also negatively affects capsaicinoid accumulation, particularly capsaicin, during critical fruit development stages, thereby reducing the pungency and market value of hot peppers [23]. Previous research has demonstrated that drought reduces phenylpropanoid pathway activity, limiting the biosynthesis of key metabolites that contribute to capsaicinoid production [23,24]. Thus, managing water availability is vital not only for maintaining yield but also for preserving the unique chemical qualities that define hot pepper cultivars.

Although the effects of drought on chili peppers have been investigated, few studies have examined how specific volumetric soil moisture content (VSMC) levels influence the physiological and biochemical traits of Capsicum chinense across different varieties under water-limited conditions—particularly using advanced tools such as soil moisture and sap flux sensors. For instance, Sun et al. [25] used a 10HS capacitance sensor (Decagon Devices, Pullman, WA, USA) to evaluate the effects of 15%, 25%, 35%, and 45% VSMC on three chili pepper varieties, whereas Pedroza-Sandoval et al. [26] assessed two varieties under VSMC levels of 20% and 25%, with soil moisture monitored in real time using a digital tensiometer (MO750, Extech Instruments Co., Laredo, TX, USA). However, there is a lack of research exploring chili pepper performance under lower VSMC thresholds (<21%) with precise, sensor-based irrigation management, which could yield valuable insights into cultivar-specific water-use strategies and their effects on yield and quality. Recent studies have demonstrated the increasing application of sap flux and sap flow sensor technologies in horticultural crops, particularly under controlled or semi-controlled environments. For instance, Zhang et al. [27] developed a flexible, plant-wearable sap flow sensor to monitor water transport dynamics in watermelon fruit stalks across different developmental stages, offering real-time physiological insights that can enhance fruit growth monitoring and irrigation precision. Mancha et al. [28] validated the use of sap flow sensors against weighing lysimeters in vineyards, demonstrating strong agreement (R² = 0.85) and supporting their use in quantifying vine transpiration under different irrigation strategies. However, despite these advancements, sap flow sensing technologies have not yet been applied to chili pepper (Capsicum spp.) under greenhouse conditions—a high-value crop that is highly sensitive to water availability. This presents a critical gap in the literature, particularly given the need for precise, crop-specific irrigation strategies in protected cultivation systems. To address the challenges posed by water stress, sensor-based irrigation technologies have emerged as effective solutions. Systems utilizing soil moisture sensors, sap flow sensors, and automated irrigation controllers allow the real-time monitoring of plant and soil water status, enabling precise and timely irrigation decisions. Technologies such as Hydra Probe sensors and Arduino-based automated irrigation systems have been successfully implemented in controlled environment agriculture to improve water-use efficiency and optimize crop growth [29,30,31]. While soil moisture and environmental sensors are commonly used, the application of sap flux sensors for monitoring plant water status remains largely underexplored in hot pepper cultivation. Sap flux measurement provides a direct, real-time indicator of whole-plant transpiration and internal water movement, offering critical insight into plant physiological responses to irrigation. By integrating sap flux monitoring in chili peppers, this study introduces a novel approach that enables the dynamic assessment of plant water demand, paving the way for more responsive and efficient irrigation strategies. These sensor-driven systems not only allow to conserve water but can promote consistent physiological performance and enhanced fruit quality under variable environmental conditions, offering a sustainable path forward for hot pepper production.

The application of precision water management strategies using sensor-based systems has gained significant attention for its potential to optimize resource use and improve crop outcomes. Several studies have demonstrated that integrating sensor technologies into irrigation scheduling leads to improved water-use efficiency, better physiological performance, and higher yields across various horticultural crops, including peppers [29,31]. However, most previous studies have primarily relied on either soil or canopy-level measurements, often overlooking the importance of integrated, multi-level monitoring. Our study addresses this critical gap by implementing a comprehensive sensor-based irrigation system that simultaneously monitors water status at the soil (via soil moisture sensors), leaf (via gas exchange measurements), and whole-plant levels (via sap flux sensors). This layered sensing approach provides a more complete understanding of plant water dynamics and enables more precise and timely irrigation decisions, representing a significant advancement in the application of precision irrigation techniques in hot pepper production. By continuously monitoring soil and plant water status, these systems allow for targeted irrigation applications that minimize water stress while avoiding over-irrigation, which can also negatively impact plant growth and fruit development.

While previous studies have assessed irrigation effects on pepper physiology or yield using isolated techniques—such as leaf-level measurements [32,33], soil moisture sensors [34], or sap flux systems [35]—very few have combined all three to assess whole-plant water use dynamics in C. chinense. Under water-limited conditions, this integration becomes especially critical for accurately characterizing plant responses and guiding precision irrigation. However, the simultaneous use of soil moisture sensors, sap flux sensors, and gas exchange tools within a unified, real-time monitoring framework remains limited in the literature, particularly for high-value specialty crops like chili pepper. This study advances the current methodology by implementing an integrated sensor-based approach to capture multiscale water use responses—from root-zone moisture to whole-plant sap transport and leaf-level transpiration—thus filling a significant gap in Capsicum research.

Moreover, as adverse weather conditions increasingly alter precipitation patterns and exacerbate water scarcity, sustainable horticultural practices must prioritize improved water-use efficiency (WUE). Precision irrigation strategies—particularly when informed by integrated sensor systems—offer an adaptive response to mitigate these challenges while supporting crop productivity. Increasing WUE in chili pepper systems has the potential to enhance profitability, conserve resources, and maintain fruit quality, particularly in controlled environments or arid climates [36,37,38].

The goal of this study was to explore the use of an integrated sensor-based irrigation system for greenhouse grown hot peppers under stratified volumetric soil moisture levels, ranging from stress to near optimal hydration, in potting media commonly used in controlled greenhouse environments. Specifically, we evaluated the morphological, physiological, yield, and phytochemical responses of three Capsicum chinense cultivars— Habanero, Helios (hybrid), and Lantern (organic)—under three volumetric soil moisture levels which were maintained consistently throughout the growing season using an automated irrigation system.

2. Materials and Methods

2.1. Experimental Site

This study was conducted in the greenhouse located at the North Carolina Agricultural and Technical State University farm, Greensboro, NC (36°04′05″ N lat. and 79°43′27″ W long). The study was carried out from April to October 2024. Three hot pepper varieties (Capsicum chinense), i.e., Habanero, Helios (hybrid habanero), and Lantern (Organic Habanero), were used in this experiment. The seeds of the three varieties were obtained from Johnny’s Selected Seeds Company, Winslow, AZ, USA. The seeds were sown in 6 by 12 cell germinating starter trays using professional growing mixture on 23 April 2024. Once seedlings reached the 8–10 true-leaf stage, they were transplanted into 11-inch potting containers (26 cm diameter and 70 cm depth) on 12 June 2024, using vegetable Potting mix (Carolina Soil Company, Kinston, NC, USA). This potting mix contained peat moss (75%), vermiculite (15%), and perlite (10%), with the addition of lime (7.11 ounces), and gypsum (3.55 ounces). Each pot was pre-perforated at the bottom to allow excess water to drain out. Greenhouse climatic conditions were monitored using the Atmos 41 Gen 2 weather station, METER Group Inc. (Pullman, WA, USA) [39]. This advanced station was utilized to record air temperature, relative humidity (RH), and solar radiation within the greenhouse from 1 May to 30 August 2024.

2.2. Experiment Design

Although the impacts of drought on chili peppers have been studied, limited research has focused on how volumetric soil moisture content (VSMC) levels 1 affect the physiological and biochemical traits of Capsicum chinense across different varieties under water-limited conditions—particularly using advanced technologies such as soil moisture sensors and sap flux sensors. To address this, the soil moisture treatment levels—Low (15%), Medium (18%), and High (21%) VSMC—were selected based on the drought stress threshold identified by Sun et al. [25], who reported significant declines in growth and physiological traits in chili pepper at substrate moisture levels below 25% VWC. The Low (15%) range was chosen to simulate clear drought stress, aligning with conditions shown to reduce photosynthesis and stomatal conductance. The Medium (18%) range represents a transition zone near the lower physiological limit for optimal function, while the High (21%) range reflects well-watered conditions, just below the field capacity for peat-based potting mixes (~25–30% VSMC). This stratification enables the evaluation of plant responses across a realistic and agronomically relevant moisture gradient—from stress to near-optimal hydration—under controlled greenhouse conditions.

The experiment was set up in a two-factor factorial randomized complete block design with soil moisture as a main factor and pepper variety as a sub-plot factor. Individual greenhouse benches served as our blocking factor (Figure 1). Each treatment combination was repeated four times. Three sensor-based drip irrigation levels were used to conduct this experiment: (1) low irrigation levels (15% of volumetric soil moisture content (VSMC)), (2) medium irrigation levels (18% of volumetric soil moisture content (VSMC)), and (3) high irrigation levels (21% of volumetric soil moisture content (VSMC)). These treatments were managed using Base Station 3200 volumetric soil moisture content (VSMC) sensors (Baseline Inc., Boise, ID, USA). Drip emitters were positioned on the surface of the potting substrate, while volumetric soil moisture content (VSMC) sensors were installed 3–4 inches deep in the center of the pot. When the VSMC levels in any treatment fell below the specified range according to various moisture treatments, the 3200S controller connected to the VSMC sensor automatically triggered irrigation until the target moisture levels for that treatment were restored. This system ensured consistent and precise moisture levels for the hot peppers in each treatment group.

During the vegetative stage, Alaska Fish Fertilizer (5-1-1) was applied at two- and four-week intervals following transplanting. Beginning six weeks after transplanting, Tiger Bloom liquid fertilizer (2-8-4, Fox Farm Soil and Fertilizer Company, Samoa, CA, USA) was introduced and applied biweekly to promote flowering and fruit development. Fertilization alternated between the two formulations throughout the growth cycle. For Alaska Fish Fertilizer, 90 mL was diluted in 2 gallons of water, with 200 mL of the solution applied per pot during the vegetative phase. For Tiger Bloom, 100 mL was diluted in 5 gallons of water, and 500 mL was applied per pot. During the reproductive stage, the fertilizer volume was increased to meet higher nutrient demands: 500 mL per pot for Alaska Fish Fertilizer and 1000 mL per pot for Tiger Bloom (

Table 1. The table represents fertilizer types, concentrations, dilution rates, and application volumes used during the vegetative and reproductive growth phases of Capsicum chinense.

Growth Stage	Fertilizer Type	Concentration	Dilution Rate	Volume Per Pot
Vegetative Phase	Alaska Fish (5-1-1)	90 mL/2 gal water	Applied at 2- and 4-week intervals	200 mL
Reproductive Phase	Tiger Bloom (2-8-4)	100 mL/5 gal water	Applied biweekly	500 mL initially, increased to 1000 mL
Reproductive Phase	Alaska Fish (5-1-1)	90 mL/2 gal water	Alternated biweekly with Tiger Bloom	Increased to 500 mL

).

2.3. Sap Flux Measurements

Sap flux measurements were conducted using heat-balance-type Dynagage sap flow sensors (SGEX series, Dynamax Inc., Houston, TX, USA) connected to a CR1000 data logger (Campbell Scientific, Logan, UT, USA). Initial calibration was performed following the manufacturer’s guidelines using baseline zero-flow readings with disconnected power [40]. The sensors were programmed to log sap flux data at 10 min intervals, later averaged to hourly and daily means for analysis. Gauges (9 mm and 13 mm) were installed on mid-canopy branches approximately 20–30 cm above soil level and were thermally insulated with reflective foil to minimize external heat interference. Sensor replacement from SGEX-9-WS to SGEX-13-WS occurred once the stem diameter exceeded 10 mm. All gauges were inspected weekly for placement integrity and recalibrated as needed.

2.4. Plant Physiological Measurements

Plant physiological parameters such as leaf-level transpiration rate (E, mmol m⁻² s⁻¹), photosynthesis rate (Pn, µmol m⁻² s⁻¹) and stomatal conductance rate (gs, mol m⁻² s⁻¹) were measured weekly from June to September 2024 using a portable photosynthesis machine (model LI-6800, LICOR Biosciences, Lincoln, NE, USA) equipped with a 6800-01A Fluorometer and light-controllers. The measurement conditions of the LI-6800 system were set at flow rate of 400 μmol/s, relative humidity at 60%, CO₂ concentration at 420 ppm, fan speed at 10,000 rpm, leaf temperature turned off, Light R90b and light intensity 1200 μmol m⁻² s⁻¹. Before logging measurements, the LI-6800 system was allowed to reach steady-state conditions for E, gs, and Pn [33,41,42]. These measurements were conducted between 9:00 a.m. and 11:00 a.m. on clear, sunny days. For each plant, one fully expanded, illuminated, and healthy leaf was selected from the upper canopy, preferably among the top-most newly developed leaves. The selected leaf was clamped into the leaf chamber, and a stable reading was recorded. For each measurement date, one measurement per plant was included in the statistical analysis across varieties and treatments.

2.5. Plant Morphological Measurements

Plant height was measured manually throughout the growing seasons at one-week intervals using a centimeter rule. At each measurement, height was measured from the surface of the soilless mix to the top of the main plant stem. Plant diameter was measured using a digital caliper 1114 purchased from Insize Company (Loganville, GA, USA) and measurements were taken in millimeters. The caliper was zeroed after every reading before moving to the next plant, and measurement was taken beneath the first true leaves.

2.6. Plant Yield

Pod harvesting began on 15 August 2024, for the Lantern and Helios varieties, which was 115 days after sowing. For the Habanero variety, harvesting commenced slightly later, on 23 August 2024, corresponding to 123 days after sowing. Pods were harvested when they reached a horticulturally green mature state (pinto stage) to maintain consistency [43]. Throughout the growing season, yield components for each variety and treatment were evaluated by quantifying the number of pods per plant (pods/plant), average pod weight (g), and total pod yield (g/plant) from all harvested fruits.

2.7. Phytochemical Analysis

Capsaicinoid concentrations were analyzed at Southwest Bio-Labs, Inc. (Las Cruces, NM, USA) using standardized protocols. Quantification of capsaicinoids and calculation of pungency (Scoville Heat Units, SHU) were performed following the HPLC-based ASTA Analytical Method 21.3. Dried pepper samples were finely ground, and 1.0 g of powder was extracted in 10 mL of HPLC-grade acetonitrile, vortexed for 30 s, and filtered for analysis following the procedure outlined by Marutani et al. [44].

Chromatographic separation was carried out on a C-18 reversed-phase column (150 × 4.6 mm, 5 μm) at 40 °C, with a mobile phase of water (A) and methanol (B) under the gradient detailed by Marutani et al. [44], monitoring at 280 nm. Capsaicin and dihydrocapsaicin were identified and quantified by comparison to external standards, with concentrations expressed as μg/g dry weight.

Scoville Heat Units (SHU) were computed according to the following equation recommended by ASTA Method 21.3 and referenced in the HPLCFactsheet.pdf:

SHU = [(capsaicin, μg/g) × 16] + [(dihydrocapsaicin, μg/g) × 16]

A correction factor of 16 was applied to each capsaicinoid to convert relative concentrations (μg/g) to SHU, reflecting their equivalent pungency contributions. The resulting values were summed to obtain the total sample pungency.

2.8. Statistical Analysis

A two-way factorial randomized complete block design was employed, with soil moisture level (Low, Medium, High) and pepper cultivar (Habanero, Helios, Lantern) as main factors. Data were analyzed using JMP (Version 18, SAS Institute, Cary, NC, USA). A two-way Analysis of Variance (ANOVA) model was applied to evaluate main and interaction effects on the following response variables:

• Physiological traits: photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (E)
• Morphological traits: plant height, stem diameter
• Yield components: number of pods, average pod weight, total yield (Mg·ha⁻¹)
• Phytochemical traits: capsaicin, dihydrocapsaicin, nordihydrocapsaicin concentrations, and total Scoville Heat Units (SHU)
• Water-use dynamics: sap flux (g·d⁻¹)

The assumptions of normality and homogeneity of variances were checked using Shapiro–Wilk Test. Where assumptions were met, fixed effect ANOVA was conducted. Significant main or interaction effects (p < 0.05) were further analyzed using Least Significant Difference (LSD) tests to separate means. Outliers were identified using boxplot visualization and removed if they exceeded 1.5 times the interquartile range, while missing data were minimal and handled through listwise deletion to maintain data integrity.

3. Results

3.1. Greenhouse Conditions

During the experimental period, the air temperature inside the greenhouse ranged from 11.4 °C to 34.0 °C, with the minimum recorded on 13 May 2024, and the maximum on 26 May 2024. The average daily minimum and maximum temperatures were approximately 19.7 °C and 28.1 °C, respectively. Relative humidity (RH) varied from 31.8% to 99.9%, reaching its lowest on 31 May 2024, and peaking on 8 July 2024. The average daily minimum and maximum RH values were 74.3% and 97.8%, respectively, (Figure 2a).

Solar radiation (W/m²) exhibited temporal fluctuations throughout the growing season, with instantaneous values ranging from 25.3 W/m² to 212.1 W/m². Based on daily maxima, solar radiation peaked at 717.4 W/m² on 7 June 2024, while the lowest daily maximum of 94.7 W/m² was observed on 14 May 2024. The average daily minimum and maximum solar radiation values were 0.0 W/m² and 542.7 W/m², respectively (Figure 2b).

3.2. Effect of Different Irrigation Levels on the Physiological Responses of Three Pepper Cultivars

The photosynthetic rate (Pn) was clearly influenced by irrigation levels, with higher values recorded under medium and low irrigation compared to high irrigation (

Table 2. Effects of pepper variety, irrigation levels, and their interaction on photosynthetic rate (Pn), transpiration rate (E), stomatal conductance rate (gs), height (cm), stem diameter (mm), fruit number (pods/plant), average fruit weight (g), average pod yield (g/plant)), Scoville Heat Unit (SHU), capsaicin (%), dihydrocapsaicin (%), nordihydrocapsaicin (%), and sap flux (g d⁻¹), among three hot pepper varieties.

Measurements	Factors	dF	F-Values	p-Values
Photosynthetic rate (Pn)	Pepper varieties	2	0.0848	0.9187
	Irrigation levels	2	7.4670	0.0007
	Pepper varieties × Irrigation levels	4	0.2659	0.8998
Transpiration rate (E)	Pepper varieties	2	0.6431	0.5263
	Irrigation levels	2	0.1149	0.8915
	Pepper varieties × Irrigation levels	4	0.1437	0.9657
Stomatal Conductance rate (gs)	Pepper varieties	2	0.0734	0.7789
	Irrigation levels	2	0.2500	0.9293
	Pepper varieties × Irrigation levels	4	0.1656	0.9558
Height (cm)	Pepper varieties	2	5.8541	0.0031
	Irrigation levels	2	8.0941	0.0003
	Pepper varieties × Irrigation levels	4	0.0283	0.9985
Stem diameter (mm)	Pepper varieties	2	5.9272	0.0028
	Irrigation levels	2	0.0223	0.9779
	Pepper varieties × Irrigation levels	4	0.3810	0.8223
Fruit number (pods/plant)	Pepper varieties	2	0.6935	0.5085
	Irrigation levels	2	0.4288	0.6557
	Pepper varieties × Irrigation levels	4	0.2874	0.8835
Average fruit weight (g)	Pepper varieties	2	6.0731	0.0066
	Irrigation levels	2	3.1694	0.0580
	Pepper varieties × Irrigation levels	4	1.4556	0.2432
Total average Pod yield (g/plant)	Pepper varieties	2	8.3747	0.0015
	Irrigation levels	2	1.6319	0.2143
	Pepper varieties × Irrigation levels	4	0.4731	0.7550
Scoville Heat Unit (SHU)	Pepper varieties	2	7.9134	0.0020
	Irrigation levels	2	0.8017	0.4590
	Pepper varieties × Irrigation levels	4	0.6756	0.6147
Capsaicin (%)	Pepper varieties	2	8.2576	0.0016
	Irrigation levels	2	2.0375	0.1499
	Pepper varieties × Irrigation levels	4	1.7591	0.1663
Dihydrocapsaicin (%)	Pepper varieties	2	6.8828	0.0038
	Irrigation levels	2	2.1381	0.1374
	Pepper varieties × Irrigation levels	4	1.7186	0.1750
Nordihydrocapsaicin (%)	Pepper varieties	2	17.7409	<0.0001
	Irrigation levels	2	0.2715	0.7643
	Pepper varieties × Irrigation levels	4	1.2146	0.3277
Sap flux rate (g d−1)	Pepper varieties	2	24.5647	<0.0001
	Irrigation levels	2	45.0686	<0.0001
	Pepper varieties × Irrigation levels	4	0.0892	0.9858

Note: The p values in boldface indicate a significant difference (p < 0.05).

, Figure 3a,b). Specifically, the Pn was 16.7% and 22.3% higher under medium and low irrigation, respectively. Throughout the growing season, the Pn showed considerable variation, ranging from 3.41 μmol m⁻² s⁻¹ to 30.63 μmol m⁻² s⁻¹ across all irrigation treatments.

The transpiration rate (E) ranged from 0.02 to 15.89 mmol m⁻² s⁻¹ across treatments during the growing season, with minimal variation attributed to irrigation levels, pepper varieties, or their interaction (Figure 4a,b; Table 2).

Stomatal conductance (gs) showed no measurable response to irrigation level, pepper variety, or their interaction (Figure 5a,b; Table 2). Throughout the season, gs values across all treatments ranged from 0.0008 to 1.8463 mol m⁻² s⁻¹.

3.3. Effect of Different Irrigation Levels on the Plant Morphology in Three Pepper Cultivars

Plant height was influenced by both irrigation level and pepper variety, while their interaction had minimal impact (Figure 6a,b; Table 2). Plants under medium and high irrigation were approximately 11.8% and 17.2% taller, respectively, compared to those under low irrigation. Among the varieties, Lantern consistently achieved the greatest height, with values around 13% and 12% higher than Helios and Habanero, respectively, underscoring varietal differences in growth. Over the course of the season, plant height ranged from 6.5 cm to 120 cm across treatments.

Stem diameter varied across pepper varieties, while irrigation level and its interaction with variety had little influence (Figure 7a,b; Table 2). Lantern’s stem diameter was 12.9% smaller than Habanero’s and 10.1% smaller than Helios’ (Figure 7b), highlighting clear varietal differences in stem thickness. Across the growing season, stem diameter ranged from 1.8 mm to 25 mm.

3.4. Effect of Different Irrigation Levels on Yield and Yield Components in Three Pepper Cultivars

Two-way ANOVA indicated that the total number of pods per plant remained relatively stable across irrigation levels, varieties, and their interaction (Figure 8a,b; Table 2;

Table 3. Comparison of various yield components (mean ± SE), i.e., number of pods (n), average pod weight (g), and average pod yield (g/plant) for three pepper varieties.

Variety	Irrigation Treatment	Number of Pods (n)	Average Pod Weight (g)	Average Pod Yield (g/Plant)
Habanero	Low	111.5 ± 11.46 (a)	6.60 ± 0.51 (a)	730.87 ± 57.03 (a)
	Medium	114.5 ± 9.43 (a)	5.67 ± 0.27 (a)	646.14 ± 50.25 (a)
	High	103.5 ± 16.15 (a)	7.48 ± 0.51 (a)	774.06 ± 125.40 (a)
Lantern	Low	97 ± 10.67 (a)	5.42 ± 0.51 (a)	508.94 ± 68.87 (a)
	Medium	101.25 ± 25.63 (a)	6.02 ± 0.96 (a)	542.25 ± 63.62 (a)
	High	95.75 ± 4.44 (a)	5.76 ± 0.51 (a)	557.84 ± 73.37 (a)
Helios	Low	95 ± 7.39 (a)	7.42 ± 0.51 (a)	704.93 ± 60.95 (a)
	Medium	117.5 ± 16.91 (a)	6.26 ± 0.24 (a)	731.72 ± 96.42 (a)
	High	113 ± 4.85 (a)	7.87 ± 0.51 (a)	883.87 ± 28.13 (a)

). In contrast, average pod weight and total pod yield varied notably among varieties, independent of irrigation treatment (p < 0.05; Figure 8d,f). Lantern produced smaller fruits—approximately 13% lighter than Habanero and 25% lighter than Helios. It also recorded the lowest total yield, producing 33.7% less than Habanero and 44.2% less than Helios. Irrigation had minimal influence on these yield parameters, and no interaction effects were detected (Figure 8c,e; Table 2 and Table 3).

3.5. Effect of Different Irrigation Levels on Average Sap Flux Rate (g d⁻¹) in Three Pepper Cultivars

The temporal variation in sap flux and soil moisture across three pepper cultivars, i.e., Habanero, Helios, and Lantern, was evaluated under three irrigation levels: low, medium, and high (Figure 9). Sap flux exhibited a consistent seasonal pattern across all cultivars, characterized by a gradual increase during the early and mid-growth stages and peaking around mid-September, which coincided with the peak reproductive phase marked by intense fruit development and high transpiration demand. This was followed by a noticeable decline in sap flux toward the end of the growing season, indicating the onset of physiological senescence and reduced water uptake as plants transitioned out of the fruiting phase. A notable difference in the relative magnitude of sap flux and soil moisture was observed across irrigation treatments. Under low and medium irrigation, sap flux remained relatively high even when soil moisture levels were limited, suggesting a strong transpirational pull and efficient water extraction by the root system to meet physiological demands. In contrast, under high irrigation, soil moisture levels consistently exceeded sap flux activity, indicating sufficient water availability and possibly a plateau in transpirational demand or reduced water uptake due to root zone saturation [45].

The magnitude and consistency of sap flux responses were strongly influenced by soil moisture levels, with higher irrigation levels supporting greater and more stable sap flux rates (Figure 9). Under low soil moisture, all cultivars exhibited suppressed and fluctuating sap flux patterns, suggesting limited water availability-hindered transpiration. In contrast, medium and high irrigation treatments supported enhanced sap flux, particularly in Helios, which consistently exhibited the highest values across all treatments. Lantern, on the other hand, maintained lower sap flux rates regardless of irrigation level, indicating a more conservative water-use strategy. These findings highlight both the sensitivity of sap flux to moisture availability and the genotypic differences in water-use dynamics among pepper cultivars.

As shown in Figure 10a,b and summarized in Table 2, significant main effects of both irrigation level and pepper variety were observed for sap flux rate, while their interaction was not significant. Sap flux increased steadily with irrigation, rising by 4% from low to medium and by an additional 3.8% from medium to high irrigation. Among the cultivars, Helios exhibited the highest sap flux rates, approximately 8.5% higher than Habanero and 10% higher than Lantern, while Lantern recorded the lowest values consistently across all irrigation levels. The daily average sap flux rate varied temporally throughout the season, ranging from 580 to 1088 g d⁻¹.

3.6. Effect of Different Irrigation Levels on Capsaicinoid Content and Pungency in Three Hot Cultivars

Pungency levels, measured in Scoville Heat Units (SHU), fluctuated over the growing season, ranging from 64,000 to 330,000 SHU across all treatments and varieties. While irrigation and its interaction with variety had little influence on the SHU (Figure 11a; Table 2), clear genotypic differences were evident. Habanero exhibited nearly twice the SHU of Lantern and more than 1.75 times that of Helios. Lantern also showed moderately higher SHU values—approximately 13% greater than Helios—highlighting strong varietal variation in pungency (Figure 11b).

Capsaicin concentration differed among pepper varieties, with Lantern showing the highest levels—approximately 7.6% higher than Habanero and 4% higher than Helios. Helios also had a slight advantage over Habanero, with a 3.5% increase (Figure 12a,b; Table 2). Irrigation level and its interaction with variety had minimal impact. Capsaicin content varied over the season, ranging from 63.5% to 82.3%.

Dihydrocapsaicin concentration varied among pepper varieties, with Habanero containing approximately 20% more than Lantern and 7% more than Helios. Although Helios had slightly higher levels than Lantern, this difference was minor (Figure 12d). Irrigation level and its interaction with variety had limited influence on dihydrocapsaicin concentration (Figure 12c; Table 2). At harvest, values ranged from 17.3% to 34.2% across treatments. Similarly, nordihydrocapsaicin concentration showed strong varietal differences. Habanero recorded the highest levels—nearly twice that of Helios and more than double that of Lantern—while Helios and Lantern exhibited comparably lower concentrations (Figure 12f). Irrigation and its interaction had little effect on this trait as well (Figure 12e; Table 2).

4. Discussion

Photosynthetic rate (Pn) was significantly influenced by irrigation level, with higher values observed under low and medium irrigation compared to high irrigation. This suggests that Capsicum chinense cultivars may activate adaptive responses under mild to moderate water stress, rather than experiencing a decline in function. This may reflect a form of stress priming, where limited water availability triggers molecular adjustments that enhance photosynthetic performance. One likely mechanism is drought stress memory, in which prior exposure to limited moisture primes the photosynthetic system for improved efficiency. Alongi et al. [46] reported that such memory effects can trigger transcriptional changes in photosynthesis-related genes, enhancing carbon assimilation under subsequent stress. Additionally, improved stomatal regulation and increased water-use efficiency (WUE) may contribute to enhanced CO₂ uptake while minimizing water loss (Table S1, Figure S1). The sustained accumulation of photosynthetic proteins such as Rubisco under moderate stress conditions may also help maintain photosynthetic performance [47].

The Pn also increased during warmer periods of the season, with peak values observed in July under elevated greenhouse temperatures. This pattern suggests that C. chinense genotypes may exhibit inherent heat tolerance, enabling them to sustain or even enhance photosynthesis under moderately high temperatures. Similar trends have been reported by Hussain et al. [48], where genotypes such as C-37 and UK-101 maintained high Pn under a 40 °C/32 °C day/night regime. In our study, the lack of a significant interaction between irrigation level and cultivar indicates that Pn responses to moisture were consistent across Habanero, Helios, and Lantern. This lack of interaction implies that irrigation response in the Pn is under strong genetic control, with limited genotype × environment modulation. Despite this uniformity, all three cultivars showed a reduced Pn under high irrigation, reinforcing the notion that excess moisture can negatively impact photosynthetic efficiency.

Our results align more closely with Okunlola et al. [22] and Nieto-Garibay et al. [49], who reported stable or improved photosynthesis under moderate water deficits, suggesting that mild stress may stimulate adaptive physiological responses. These findings contrast with studies showing substantial reductions in the Pn under severe drought such as Kulkarni and Phalke [50], Goto et al. [51], and Ou and Zou [52]. For instance, Ou and Zou [52] reported a ~90% reduction in the Pn in C. chinense under extreme drought, a condition far more severe than the controlled irrigation levels applied in our greenhouse study. This demonstrates the potential of sensor-managed irrigation systems to optimize photosynthetic performance by maintaining plants within their adaptive stress thresholds.

In Capsicum chinense, transpiration (E) is closely regulated by stomatal conductance (gs), which controls water vapor loss through leaf pores. Under stable environmental conditions—such as consistent temperature and humidity—soil moisture variation may have limited impact on E if gs remains steady. This relationship is well-documented, with studies by Erwin et al. [53] and Zhang et al. [54] reporting strong positive correlations between gs and E, consistent with our observed correlation of 0.8 (Figure S2). The relatively stable E across irrigation treatments in this study may reflect an adaptive mechanism that enables C. chinense to maintain gas exchange efficiency while minimizing water loss under moderate moisture stress.

Contrasting findings have been reported in other studies, where significant variation in transpiration (E) occurred among pepper varieties and irrigation treatments, particularly under abrupt or field-imposed stress conditions [26,53,55]. Reductions in E are commonly linked to short-term or severe drought, often driven by rapid stomatal closure to minimize water loss [51,56,57]. In contrast, consistent and moderate irrigation—such as in our controlled greenhouse setup—may promote more stable transpiration rates. This stability could reflect enhanced drought resilience or efficient stomatal control, particularly in genotypes adapted to arid conditions, as suggested by Nieto-Garibay et al. [49].

Stomatal conductance (gs) values observed in this study were generally higher than those reported by Erwin et al. [53], who documented a range of 0.00001 to 0.00028 mol H₂O m⁻² s⁻¹ across five Capsicum species. In Lantern, gs increased with irrigation but remained consistently lower than in Helios and Habanero, suggesting a more conservative water-use strategy. This aligns with Widuri et al. [57], who found that gs in hot peppers declined significantly under drought and remained higher in well-watered plants. Lantern’s relatively restrained gs values suggest a physiological adaptation characterized by lower integrated stomatal conductance, potentially reducing cumulative water loss while maintaining sufficient gas exchange for photosynthesis. Such behavior is characteristic of drought-adaptive strategies and may be beneficial under fluctuating or low-moisture conditions. In contrast, Habanero displayed a more variable gs pattern, consistent with findings by Goto et al. [51], who reported reduced gs in Habanero under both drought and waterlogging stress, suggesting sensitivity to moisture extremes.

The findings of this study highlight the importance of selecting hot pepper varieties based on their water-use efficiency and irrigation responsiveness. Helios consistently exhibited the highest sap flux rate compared to Lantern and Habanero, suggesting a greater inherent capacity for water uptake and transpiration. This aligns with Park et al. [58], who emphasized that sap flow can serve as a reliable indicator of plant water demand.

Stem diameter in this study was primarily influenced by varietal differences rather than irrigation levels. Habanero and Helios exhibited significantly thicker stems than Lantern, suggesting that stem thickening is largely genetically regulated under controlled greenhouse conditions. This aligns with previous findings that stem diameter is a heritable trait governed by multiple QTLs [59,60]. Similarly, Abdelkhalik et al. [61] reported no significant effects of deficit irrigation on stem diameter in Capsicum annuum, reinforcing the limited impact of moderate water stress on this trait. However, under more severe or variable environmental conditions, water stress may exert a stronger influence. For example, Macias-Bobadilla et al. [62] and Mohammed and Hussen [63] documented stem diameter reductions under drought or prolonged deficit irrigation in field-grown plants, particularly in clay soils. These contrasting findings may reflect differences in cultivar sensitivity, soil type, or stress duration. Overall, our results suggest that under greenhouse conditions, stem diameter in Capsicum chinense is predominantly shaped by genotype rather than irrigation level.

In contrast to stem diameter, plant height was more responsive to irrigation treatments. Significantly taller plants were observed under medium and high irrigation, likely due to improved vegetative growth supported by adequate water availability, which promotes cell expansion and elongation. Similar trends have been reported in Capsicum species under well-watered conditions [22,64,65]. Ahmed et al. [66] and Morgan et al. [67] also found that deficit irrigation reduced plant height, particularly in sensitive cultivars like jalapeño. However, some studies have noted varietal stability under water stress; for example, Abdelkhalik et al. [61] reported no height differences across irrigation levels in sweet pepper. In our study, Lantern consistently attained the greatest height under medium and high irrigation, suggesting strong responsiveness to favorable moisture conditions. This supports its agronomic potential for cultivation in more humid environments or under irrigation regimes that favor vigorous canopy development. These results highlight the genotype-specific interaction with irrigation and the need to tailor water management practices to maximize vegetative development and canopy structure in different cultivars.

The number of pods per plant was not significantly affected by irrigation treatments, a result consistent with Jeeatid et al. [68], who found no notable differences among three Capsicum chinense cultivars across four water stress levels, except for BGH1719. Similarly, Ruiz-Lau et al. [69] observed stable fruit numbers under varying water deficits, though the control consistently produced the highest yields. In contrast, Ahmed et al. [66] reported a reduction in fruit numbers during early and mid-harvest stages under deficit irrigation, and Khan et al. [70] found that fruit count declined more sharply than individual fruit weight under water stress. These discrepancies likely stem from differences in cultivar sensitivity, timing of stress exposure, and experimental conditions. Overall, our findings suggest that pod number in C. chinense may be less sensitive to moderate water stress than other yield components, with genotypic traits playing a more dominant role.

In this study, average pod weights increased under high irrigation, supporting enhanced fruit development in well-watered conditions. This contrasts with Zamljen et al. [71], who reported higher average pod weights (9.1 g) for Capsicum chinense, suggesting that fruit size may also depend on genetic and environmental interactions. Ferrara et al. [56] observed a substantial reduction in Capsicum annuum fruit weight during reproductive stages under deficit irrigation, with weights dropping from 166 g to 39 g, highlighting the sensitivity of this trait to water availability. Notably, Helios recorded the highest yield and pod weight under high irrigation in our study. This performance under full irrigation highlights Helios’ suitability for intensive production systems with sufficient water supply. This differs from Khan et al. [70], who found reduced yields in C. annuum and C. frutescens under both excessive and limited irrigation, indicating an optimal irrigation threshold for maximizing yield. These results underscore the importance of cultivar-specific irrigation strategies, as Helios appears well suited for intensive, high-input systems, while Habanero may maintain stable productivity under moderate water stress.

Sap flux measurements in this study revealed clear sensitivity to irrigation levels and varietal differences, reflecting inherent variation in water uptake and transpiration demand among Capsicum chinense cultivars. Helios consistently exhibited the highest sap flux across all irrigation treatments—approximately 8.5% higher than Habanero and 10% higher than Lantern—indicating a stronger capacity for water uptake and higher transpirational demand. This behavior demonstrates enhanced hydraulic activity and highlights Helios’ suitability for high-input systems where water is not limiting and maximizing biomass and yield is the goal [72]. In contrast, Lantern maintained the lowest sap flux and stomatal conductance values regardless of irrigation level, reflecting a conservative water-use strategy. This may result from lower integrated stomatal conductance or tighter xylem regulation, which supports sustained physiological function under limited moisture conditions and makes Lantern a more suitable choice for water-limited environments.

For illustration, the Figure S3 graph shows the diurnal patterns of soil moisture, moisture loss, solar radiation, and sap flux rate in pepper plants (Helios variety) under low irrigation over a period of 7 days. As solar radiation rises during the day, both sap flux and moisture loss increase, reflecting higher transpiration demand. Soil moisture steadily declines through daytime periods until it reaches a set lower threshold, at which point automated irrigation replenishes moisture back to the upper limit. This cycle repeats daily, with minimal moisture loss occurring at night when solar radiation and sap flux approach zero. The graph clearly illustrates how solar radiation drives daily transpiration, influencing sap flux and soil water depletion, while precision irrigation maintains stable soil moisture within the treatment range.

Compared to previous studies, the sap flux values recorded here, particularly under low irrigation, remained relatively high, suggesting a degree of drought resilience in the Capsicum chinense genotypes evaluated. This contrasts with results from Sato et al. [73], who observed sap flux rates approaching zero under drought stress in Capsicum annuum. The continued activity under reduced irrigation in our study implies either a capacity to maintain physiological function despite moisture limitations, potentially due to differences in stomatal regulation or root water uptake efficiency or difference in plant stress levels. These findings also support earlier work by Agele et al. [74] and Yao et al. [75], who highlighted sap flux as a valuable metric for assessing varietal adaptability and plant responses to hydrological stress under differing irrigation regimes.

The stability of SHU across irrigation levels in this study suggests that soil moisture had minimal influence on total capsaicinoid accumulation in the tested Capsicum chinense varieties. This observation is consistent with previous findings by Phimchan et al. [76], who reported only a slight decline in SHU under drought conditions. Similar outcomes were also reported by Jinagool & Arom [77], indicating no significant difference in SHU when moisture availability was moderately reduced. In contrast, studies such as Zamljen et al. [71] and Guijarro-Real et al. [78] documented SHU reductions under deficit irrigation, particularly in highly pungent cultivars, highlighting cultivar-specific sensitivity to water stress. The increase in SHU under medium irrigation for varieties like Helios and Habanero may reflect an optimal physiological balance, where mild water stress enhances capsaicinoid biosynthesis via the activation of the phenylpropanoid pathway, consistent with previous reports [79].

However, despite the relative stability in total SHU, the concentrations of individual capsaicinoids—particularly dihydrocapsaicin and nordihydrocapsaicin—varied significantly among cultivars, indicating potential genotype-specific regulation of biosynthetic enzymes in response to irrigation. This contrast suggests that while the total pungency remains constant, underlying metabolic shifts in the composition of capsaicinoids may be occurring. Such variability is likely due to differences in the gene expression of capsaicinoid biosynthesis-related enzymes, such as capsaicin synthase (CS), acyltransferases, and hydroxylases, influenced by both genotype and environmental conditions.

Despite variable responses to irrigation, varietal differences exerted a stronger influence on SHU than water availability. Habanero consistently exhibited higher pungency than Lantern and Helios, aligning with prior studies identifying genotype as the dominant factor affecting SHU [80,81]. These differences likely stem from a variation in the expression or activity of key enzymes—notably phenylalanine ammonia-lyase (PAL), cinnamic acid 4-hydroxylase (C4H), and capsaicin synthase (CS)—which are tightly regulated under environmental stress. This supports the hypothesis that genetic architecture primarily governs pungency traits, and that genotype × environment interactions modulate capsaicinoid accumulation only under certain thresholds.

Capsaicin concentration remained relatively constant across irrigation levels, reinforcing the idea that environmental moisture does not significantly regulate its biosynthesis. This aligns with studies by Jinagool & Arom [77] and Phimchan et al. [79], who similarly found minimal change in capsaicin content due to moisture variation. However, divergent responses in other reports—where some cultivars increased capsaicin under both deficit [69,82] and high-moisture conditions [83,84]—imply that irrigation responsiveness is genotype-dependent. In our study, the consistency of capsaicin concentrations reinforces that, for tested C. chinense varieties, irrigation has a lesser role in influencing this compound than the genetic predisposition of the cultivar.

Significant varietal differences in capsaicin concentration further support the genetic control of this trait. Lantern recorded the highest levels, differing significantly from Habanero, while Helios remained intermediate. This trend echoes earlier research [68,78], which identified variety-specific differences in capsaicin accumulation based on differential gene expression or enzyme activity across the biosynthetic pathway. As discussed by Phimchan et al. [79], enzymes like PAL, C4H, and CS serve as regulatory nodes, meaning that genotypes with inherently high baseline expression may accumulate more capsaicin, regardless of irrigation inputs.

Regarding dihydrocapsaicin, no significant differences were found across irrigation levels in most cultivars, implying limited environmental influence. However, the distinctively higher levels in Habanero and lower levels in Lantern suggest strong genetic control. These findings diverge from those of Haris et al. [85], who found increased dihydrocapsaicin concentrations under drought, especially post-anthesis, with levels rising from 100 µg/g in controls to 260 µg/g under severe stress. This discrepancy points to species-specific or even intra-specific (cultivar-level) differences in how water stress modulates enzyme activity related to dihydrocapsaicin synthesis.

Habanero’s elevated dihydrocapsaicin under higher moisture suggests that its biosynthetic machinery benefits from improved hydration, possibly through the enhanced expression of acyltransferase genes involved in chain elongation or condensation reactions. Lantern’s decline under similar conditions may reflect downregulation or enzyme inhibition under excess moisture, supporting the idea of negative feedback in biosynthesis under saturated conditions. Helios’ stability across treatments points to the constitutive expression of relevant genes, making it less responsive to environmental changes.

In the case of nordihydrocapsaicin, Guijarro-Real et al. [78] noted that it typically represents ≤10% of total capsaicinoids in Capsicum species. Our results confirm this, with nordihydrocapsaicin levels showing minor fluctuations across varieties and irrigation levels. While irrigation had no significant effect on Lantern and Helios, Habanero exhibited the highest levels under high irrigation, suggesting that moisture may influence nordihydrocapsaicin accumulation in select genotypes. This might be due to the upregulation of specific acyltransferases or hydroxylases downstream in the biosynthetic pathway, contributing to shifts in capsaicinoid profiles in response to irrigation regimes.

Overall, our findings indicate that genetic control plays a predominant role in determining physiological and biochemical traits in C. chinense, as supported by the minimal interaction effects observed between cultivar and irrigation treatment for most parameters. While moderate irrigation changes induced physiological adaptations such as enhanced photosynthesis and maintained sap flux, yield and quality traits were largely shaped by cultivar identity.

Study limitations include the use of a single growing season and greenhouse conditions, which may not capture seasonal variability or complex field-level environmental interactions. Future work should validate these findings across multiple seasons and under diverse thermal and photoperiodic regimes to improve scalability. Additional studies incorporating transcriptomic or proteomic data could further clarify the molecular basis of observed varietal differences and their interaction with irrigation.

5. Conclusions

This study demonstrated significant varietal effects on plant height, stem diameter, sap flux rate, average fruit weight, total pod yield, overall pungency (Scoville Heat Units, SHU) and individual capsaicinoid concentrations. In contrast, soil moisture treatments significantly influence only photosynthesis rate, plant height, and sap flux rates under the integrated sensor-based irrigation system. Among three cultivars, Helios exhibited up to 10% higher sap flux rates and achieved the highest average pod yield (883.87 g/plant) under high irrigation (21%), indicating strong adaptability to well-watered conditions. In contrast, Habanero maintained high pungency levels, recording nearly double the SHU of other varieties, even under low irrigation, highlighting its superior drought tolerance and enzymatic efficiency in capsaicinoid biosynthesis. It is important to note that while SHU values reflect total capsaicinoid content and overall pungency, individual capsaicinoid concentrations such as capsaicin provide insight into the chemical composition. Lantern recorded the highest capsaicin concentration (79.3%) and the highest transpiration rate (5.03 mmol H₂O m⁻² s⁻¹) under high irrigation, indicating a distinct water-use strategy suitable for high-moisture environments.

These findings highlight the potential of integrating plant-and-soil-based sensors into automated irrigation systems to enable real-time monitoring and precise maintenance of consistent soil moisture across stratified volumetric soil moisture levels to optimize both water-use efficiency and fruit quality in hot pepper production. Given the single-season greenhouse framework, this research represents a preliminary investigation into cultivar-level water use responses. Future studies should validate these results under multi-season and field conditions to improve scalability and practical applicability. Subsequent studies should also evaluate not only irrigation volume but also frequency, timing, and interaction with temperature, as well as temporally segment physiological responses across key phenological stages (vegetative growth, flowering, fruit set, and maturation). Such approaches would refine sensor-driven irrigation management, inform breeding programs targeting drought tolerance or elevated capsaicinoid content, and guide growers in selecting cultivar–irrigation combinations tailored to production objectives and resource constraints.