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Article

Combined Effects of Magnetized Irrigation and Water Source on Italian Lettuce (Lactuca sativa L. var. ramosa Hort.) Growth and Gene Expression

by
Xueying Yao
1,2,
Xiaofan Wang
1,
Mingshan Qu
3,
Yibo Wei
4,
Feifei Shan
1,* and
Youli Li
1,*
1
Intelligent Equipment Research Center, Beijing Academy of Agriculture and Forestry Sciences, Beijing 100097, China
2
College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430072, China
3
Beijing Agricultural Technology Extension Station, Beijing 100029, China
4
Information Technology Research Center, Beijing Academy of Agriculture and Forestry Sciences, Beijing 100097, China
*
Authors to whom correspondence should be addressed.
Agronomy 2024, 14(11), 2621; https://doi.org/10.3390/agronomy14112621
Submission received: 27 September 2024 / Revised: 3 November 2024 / Accepted: 4 November 2024 / Published: 6 November 2024
(This article belongs to the Section Water Use and Irrigation)
Browse Figures
Review Reports Versions Notes

Abstract

:
Agricultural water scarcity has become a global issue. Optimizing irrigation water quality and effectively utilizing non-conventional water resources are essential strategies to alleviate pressure on agricultural water use and achieve sustainable development. This study employed Italian lettuce as the test crop to explore the effects of magnetization treatment (M) at a magnetic field strength of 0.2 T and various irrigation water sources (T) on its growth. The following six treatments were established: fresh water irrigation (M0T1), recycled water irrigation (M0T2), saline water irrigation (M0T3), magnetized fresh water irrigation (M1T1), magnetized recycled water irrigation (M1T2), and magnetized saline water irrigation (M1T3). The results showed that the magnetization treatment increased the electrical conductivity (EC), power of hydrogen (pH), and dissolved oxygen (DO) of the three water sources compared to the non-magnetized treatment. Furthermore, magnetized irrigation with fresh water, recycled water, and saline water increased the contents of nitrogen (N), potassium (K), calcium (Ca), and magnesium (Mg) in lettuce. It also led to increases in the contents of soluble proteins (by 9.27% to 22.25%), soluble sugars (by 13.45% to 20.50%), and vitamin C (VitC) (by 4.18% to 19.33%) in lettuce. Additionally, it enhanced the above-ground fresh weight of lettuce (by 9.36% to 8.81%) and water productivity (WPc) (by 5.85% to 10.40%), while reducing water consumption. Among these treatments, magnetized fresh water irrigation was the most effective in improving quality, fresh weight, and WPc, followed by magnetized recycled water. Gene expression analysis revealed that differentially expressed genes (DEGs) were primarily enriched in metabolic pathways such as the MAPK signaling pathway—plant, phytohormone signaling, and cysteine and methionine metabolism. In summary, magnetized irrigation significantly enhanced DO levels in irrigation water, along with the fresh weight, quality, and WPc of lettuce, demonstrating its effectiveness as an efficient method for agricultural irrigation.

1. Introduction

Farmland irrigation plays a critical role in global agriculture, utilizing approximately 1131 billion cubic meters of water annually, representing 87.1% of the total water consumed by human activities, and is essential for increasing food production and ensuring the stability of food supply [1]. However, economic development and population growth have led to increased water consumption in industry, agriculture, and domestic life, exacerbating water scarcity [2].
Therefore, the rational development and utilization of low-quality water resources are significant for addressing water shortages. Magnetized irrigation is a novel water treatment technology that primarily disrupts hydrogen bonds between water molecules through the application of a magnetic field, resulting in smaller clusters of water molecules. The formation and disruption of hydrogen bonds alter the microstructure of water and enhance its polarity [3,4,5]. Research has shown that magnetized water enhances soil porosity, increases saturated hydraulic conductivity, and improves the exchange capacity of calcium ions at the soil surface, thereby improving the physicochemical properties of both water and soil [6]. Additionally, magnetized water irrigation alters the composition and proportion of soil salt base ions, with a more pronounced eluviation effect on Na+, Cl−, and SO42− [7]. Moreover, magnetized irrigation promotes root activity and growth, enhances the absorption of soil water by wheat, and thereby increases both the yield and average water-use efficiency of winter wheat [8]. Similarly, fresh water with magnetized irrigation results in a significant increase in net photosynthesis rate (Pn) and instantaneous water-use efficiency (iWUE) in cotton, promoting growth morphogenesis and biomass accumulation by enhancing photosynthesis and water-use efficiency [9]. Furthermore, magnetized water irrigation increases crop yields and enhances crop quality. For instance, magnetized brackish water irrigation significantly enhances soil water retention, reduces salt accumulation, and boosts both cotton growth and yield, especially at a magnetic intensity of 4000 Gs, making it a promising method for mitigating salt stress in arid regions [10]. Magnetized water irrigation has been shown to increase tomato dry matter accumulation and yield by approximately 20% [11]. Despite these promising results [12,13,14], relatively few studies have focused on the effects of magnetized water irrigation on lettuce growth, indicating a gap in current research that must be addressed.
Currently, irrigation water sources mainly include fresh water, recycled water, and saline water [15]. However, the effects of magnetized water irrigation vary based on factors such as water source, crop type, and environmental conditions, making it challenging to draw uniform conclusions regarding its impact on crop growth [16]. The effects of magnetization treatments largely depend on water-source characteristics, with magnetized brackish water irrigation significantly improving major growth indices in cotton seedlings compared to fresh and brackish water irrigation [17]. Existing studies primarily focus on single types of irrigation water, mainly exploring the phenotypic effects of magnetized water irrigation on crops. However, the molecular mechanisms underlying these effects, especially under various irrigation water sources, remain underexplored. With the growing application of high-throughput sequencing technology in plant stress research, the integration of phenotypic and transcriptomic data allows for a deeper understanding of the complex relationships between plant phenotype and gene expression. For example, transcriptome data analysis has revealed key markers for optimizing irrigation timing in rice under alternating wetting and drying (AWD) irrigation [18]. Similarly, transcriptomic analysis in potato under varying levels of drought stress has uncovered the molecular mechanisms involved in starch and sucrose metabolic pathways [19]. Additionally, transcription factor families in the tomato genome, such as ERF, WRKY, MYB, and bHLH, are likely involved in interactions with the southern root-knot nematode and play critical regulatory roles in the plant’s response to nematode infestation [20]. Therefore, this study aims to systematically investigate the effects of magnetized water irrigation on lettuce growth and its molecular mechanisms under different water sources. By integrating transcriptomic and phenotypic data, it seeks to establish a scientific foundation for optimizing irrigation strategies and exploring potential applications of magnetized water irrigation in agriculture.
This study explored the effects of non-magnetized and magnetized treatments on water quality parameters, mineral element content, quality, yield, and water productivity (WPc) of lettuce irrigated with fresh water, recycled water, and saline water. Transcriptome analysis was used to reveal how magnetized irrigation affects lettuce growth and quality through gene expression regulation. The molecular regulatory mechanisms of magnetized irrigation on lettuce growth were explained.

2. Materials and Methods

2.1. Test Materials

The experiment was conducted in 2018 and 2019 in a solar greenhouse at the National Precision Agriculture Demonstration Base in Xiaotangshan Town, Changping District, Beijing, China (116°26′ E, 40°10′ N, 35 m altitude). Italian lettuce (Lactuca sativa L. var. ramosa Hort.) sourced from the Jiangsu Academy of Agricultural Sciences was chosen as the experimental material. Plastic pots with an inner diameter of 28 cm and height of 23 cm were used. Each pot was filled with 10 kg of air-dried soil, with physicochemical properties shown in Table 1 and Table 2. A one-time base fertilizer application included 1.96 g of urea (46% N), 1.91 g of diammonium phosphate (12% N, 42% P2O5), and 1.92 g of potassium sulfate (52% K2O), which were thoroughly mixed with the soil, with no additional fertilization during the growing period. The layout of the magnetized water device is shown in Figure 1A. A 50 L bucket served as the irrigation water source. Water flowed through the magnetizer at a specific rate, causing water molecules to resonate and form magnetized water. Irrigation water was pressurized by a 750 W booster pump, achieving a flow rate of 2.2 m3/h through a 32 mm diameter PVC pipe at a pressure of 0.30 MPa. To ensure effective magnetization, water was circulated through the system 5–6 times over 5 min. A schematic view of the magnetizer is shown in Figure 1B. Irrigation water was treated with an Act-type permanent magnetizer (Act-type, Shanghai Xuantong Energy Technology Co., Shanghai, China), which uses sintered neodymium magnets (NdFeB) with a magnetic field strength of 0.2 T. This design ensured that water remained magnetized as it flowed through the magnetizer, supporting subsequent irrigation processes.

2.2. Experimental Design

The experiment was designed to test the interaction of the two following factors: magnetization treatment (M) and irrigation water source (T), using a randomized complete block design. Magnetization treatment included two levels, namely non-magnetization(M0) and magnetization (M1), while irrigation water included three levels, namely fresh water (T1), recycled water (T2), and saline water (T3). This combination resulted in six treatments, listed as follows: fresh water irrigation (M0T1), recycled water irrigation (M0T2), saline water irrigation (M0T3), magnetized fresh water irrigation (M1T1), magnetized recycled water irrigation (M1T2), and magnetized saline water irrigation (M1T3). Each treatment was replicated three times in a randomized block design, with 30 pots per replicate. Fresh water was sourced from groundwater at the experimental site, while recycled water was secondary effluent treated at the Beijing Bishui Water Reclamation Plant, meeting the Water Quality Standard for Recycling of Urban Wastewater for Agricultural Irrigation (GB20922-2007 [21]). Saline water (mineralization of 2.46 g/L) was prepared by adding analytical-grade sodium chloride at a concentration of 2 g/L to fresh water. Before planting, each pot was irrigated with 4 L of fresh water to allow the soil to naturally settle. Planting was performed when soil moisture reached approximately 60% of field water-holding capacity. In both the 2018 and 2019 experiments, lettuce seedlings at the six-leaf, one-center stage were transplanted on 24 November 2018, and 26 October 2019, respectively, with one seedling per pot. Harvesting occurred on 28 January 2019, and 2 January 2020, for the two respective experiments, with a growth period of approximately 68 days. Irrigation was managed by setting 80% of field water-holding capacity as the lower limit and 95% as the upper limit. Soil moisture content was calculated using the weighing method, and irrigation was applied when soil moisture dropped to the lower limit, bringing it back to the upper limit.

2.3. Measurement Indicators and Analytical Methods

2.3.1. Irrigation Water Quality

Electrical conductivity (EC), pH, and dissolved oxygen (DO) levels of the irrigation water were measured at room temperature (20 ± 2 °C). EC was determined using a conductivity meter (Remco DDSJ-308F, Shanghai Yidian Company, Shanghai, China), while pH and DO levels were measured using a portable meter equipped with PHC301 and LDO101 sensors (HQ40d, Hach America, Inc., Loveland, CO, USA).

2.3.2. Mineral Content of Lettuce

After harvesting, lettuce leaves were collected, dried, and ground to determine mineral element contents. Nitrogen (N) content was determined by the Kjeldahl method [22]. Phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sodium (Na) contents were measured using inductively coupled plasma optical emission spectrometry (ICP-OES, model 715-ES, Agilent, Santa Clara, CA, USA) [23].

2.3.3. Effects on Lettuce Quality, Yield, and WPc

The fresh weight of the above-ground part, measured using the weighing method, represents lettuce yield. The lettuce was subjected to leaf fixation in a drying oven at 105 °C for 15 min, followed by drying at 60 °C until a constant weight was achieved to determine the dry weight. Soluble sugars, soluble proteins, and VitC contents in lettuce leaves were measured using the anthrone colorimetry method, Coomassie Brilliant Blue G-250 staining method, and 2,6-dichlorophenol indophenol (DCIP) titration method, respectively [24].
Each plastic pot’s weight was measured daily using an electronic scale, followed by irrigation to maintain specified water limits, with data recorded at 8:00 a.m. Daily water consumption was determined by calculating the difference in weight between two consecutive measurements at the same time the next day. When irrigation was applied, daily water consumption was calculated as the pot’s weight plus the irrigation volume, minus the weight recorded the following day. The calculation for WPc is as follows:
W P c = Y / E T
In the equation, WPc represents crop water productivity (kg/m3); Y represents crop yield (kg/hm2); and ET represents crop evapotranspiration (m3/hm2).

2.3.4. Lettuce Transcriptome Sequencing

Lettuce plants exhibiting uniform growth, free from mechanical damage or disease, were selected. Three leaves from each treatment were collected, mixed in equal quantities, and each treatment was replicated three times. Samples were flash-frozen in liquid nitrogen and stored at −80 °C. Total RNA was extracted using TRIzol reagent (Qiagen, Hilden, Germany), purified with a plant RNA purification kit (Nanodrop 2000), and a transcriptome library was constructed and sequenced on the Illumina HiSeq 2000 platform at the Institute of Biotechnology, Beijing Academy of Agricultural and Forestry Sciences, Beijing, China. Principal component analysis (PCA) was performed using the fragments per kilobase of exon model per million-mapped-fragment (FPKM) values of all annotated genes from the 18 transcriptome samples. Clean reads were aligned to the reference genome using HISAT2 software (version 2.1.0), and differentially expressed genes (DEGs) were analyzed using the R package DEGSeq (version 1.12.0) [25]. Three comparison groups were analyzed based on different irrigation water sources, listed as follows: M1T1 vs. M0T1, M1T2 vs. M0T2, M1T3 vs. M0T3. DEGs were identified with thresholds of p-value < 0.01 and log2FoldChange > 1. Gene ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed using Goseq R package (version 1.10.0) and KOBAS (version 2.0) software, respectively. Transcription factors were identified from the DEGs using iTAK (vision 18.10) software [26].

2.4. Data Processing

Data were organized and analyzed using Microsoft Excel 2010, and statistical analyses were performed using DPS 7.05 software. Multiple comparisons were conducted using Duncan’s new multiple range test (MRT), and graphical analyses were performed using Origin 2019.

3. Results

3.1. Effect of Magnetization Treatment on the Water Quality

Irrigation water quality parameters for each treatment are shown in Table 3. Magnetization treatment increased the EC, pH, and DO levels in fresh, recycled, and saline water. Compared to non-magnetized treatment, EC in the three magnetized water sources increased by 1.61%, 1.04%, and 0.69%, respectively; these differences were not significant. pH increased by 7.00%, 5.70%, and 6.52%, and DO increased by 11.03%, 9.94%, and 10.27%, respectively, with all reaching significant levels. Differences in EC, pH, and DO were observed between water sources, as shown in Table 3. EC in saline water and pH in recycled water were significantly higher than in other water sources, while fresh water had the highest DO. Analysis of Variance (ANOVA) (Table 4) produced similar results, indicating that both magnetization treatment and water source had highly significant effects on pH and DO (p < 0.01), while the effect of water source on EC was also highly significant (p < 0.01).

3.2. Effect of Magnetized Water Irrigation with Different Water Sources on the Content of Mineral Elements in Lettuce

As shown in Figure 2, treatments M1T1, M1T2, and M1T3 affected the contents of N, K, Ca, and Mg in lettuce. Compared to non-magnetized treatments, the average N content in lettuce treated with M1T1, M1T2, and M1T3 increased by 7.16%, 5.81%, and 7.64%, respectively, with M1T1 and M1T2 reaching significant levels. K content increased by 5.81%, 3.73%, and 2.11%; Ca content increased by 7.64%, 5.80%, and 3.63%; and Mg content increased by 7.34%, 6.66%, and 6.31%, with M1T1 and M1T3 reaching significant levels. P content in M1T1 was 7.57% higher than in M0T1, though this difference was not significant. ANOVA results (Table 5) indicated that magnetized irrigation significantly affected N, K, Ca, and Mg levels, with the effect on N being highly significant (p < 0.01). Furthermore, Table 5 shows that mineral element contents vary among lettuce plants irrigated with different water sources, with significant differences in N, P, and Mg (p < 0.05).

3.3. Effect of Magnetized Water Irrigation with Different Water Sources on Quality, Yield, and WPc of Lettuce

Magnetized irrigation with fresh water, recycled water, and saline water improved lettuce quality, as shown in Table 6. Compared to the non-magnetized treatments, M1T1 increased the contents of soluble protein, soluble sugar, and VitC by 22.25%, 20.39%, and 19.33%, respectively, with significant differences observed (except for VitC in 2019). M1T2 and M1T3 showed increases of 24.22%, 20.50%, and 9.73%; and 9.27%, 13.45%, and 4.18%, respectively, with soluble protein under M1T2 reaching significant levels. Soluble protein content in M1T1 lettuce was the highest and significantly higher than in M1T3. The soluble sugar content in 2018 was slightly higher than in M1T2, but the difference was not significant, while it was significantly lower than M1T3 in 2019. In 2018, soluble sugar content was slightly higher in M1T2, though not significantly, while in 2019, it was significantly lower than in M1T3. VitC content in 2018 was significantly higher than in M1T2 and M1T3, while in 2019, no significant differences were observed among the treatments. Overall, the impact of magnetized irrigation on lettuce quality followed the trend of soluble protein > soluble sugar > VitC, with M1T1 showing the most pronounced improvement, followed by M1T2. ANOVA results (Table 7) indicated that both magnetization and water source significantly influenced lettuce quality, with magnetization having highly significant effects on soluble protein and soluble sugar (p < 0.01) and water source exerting a highly significant effect on soluble protein (p < 0.01).
The results in Table 6 indicate that magnetized irrigation with various water sources increased the fresh and dry weights of the above-ground part of lettuce, reduced water consumption (except for fresh water), and improved WPc. The fresh and dry weights of lettuce in M1T1, M1T2, and M1T3 increased by 9.58% and 9.36%, 8.81% and 11.42%, and 4.21% and 6.08%, respectively, while WPc increased by 9.06%, 10.40%, and 5.85%. Compared to non-magnetized irrigation, both fresh weight and WPc in M1T1 and M1T2 reached significant levels. M1T1 had the highest fresh and dry weights, though the difference compared with M1T2 was not significant. Water consumption in M1T3 was significantly lower than in the other two magnetized irrigation treatments. No significant difference in WPc was found between M1T1 and M1T2, but both were significantly higher than M1T3. Furthermore, Table 7 indicates that magnetized irrigation had a highly significant effect on fresh weight and WPc (p < 0.01), though its effect on water consumption was not significant. However, water source had a highly significant effect (p < 0.01).
Additionally, Table 6 shows that the soluble protein, soluble sugar, VitC content, fresh weight, and WPc in M1T2 were higher than in M0T1, with fresh weight and WPc reaching significant levels. Water consumption in M1T2 was lower than in M0T1, with the difference significant in 2018. This suggests that the magnetization treatment of recycled water can be used as a supplement to fresh water for agricultural production irrigation.

3.4. Transcriptome Analysis of Lettuce with Magnetic Irrigation

3.4.1. Correlation Analysis of Gene Expression and PCA Among Sequencing Samples

Before analyzing differential gene expression across treatments, it is essential to examine the correlation of gene expression levels among samples. As shown in Figure 3, the results indicate high similarity among replicate samples, indicating good reproducibility and meeting experimental requirements. Based on this analysis, the transcriptomic data quality and reliability are confirmed to be high.

3.4.2. Screening and Statistics of DEGs

To examine the effect of magnetized irrigation with various water sources on lettuce gene expression, up-regulated and down-regulated DEGs were compared among treatment groups. Figure 4 shows a total of 7586 DEGs screened across seven treatment comparison groups (this number represents the union of the DEGs from all differential expression sets), with the number of DEGs in each group ranging from 154 to 3334.
As shown in Figure 5, magnetized water irrigation influenced lettuce gene expression, with more up-regulated DEGs than down-regulated DEGs. Lettuce irrigated with magnetized saline water exhibited 338 and 215 more DEGs than those irrigated with magnetized fresh and recycled water, respectively. This suggests that magnetized saline water irrigation may induce more complex genetic changes, affecting lettuce growth and development.

3.4.3. Go Enrichment Analysis of DEGs

To comprehensively analyze DEGs in lettuce irrigated with magnetized water from three sources, GO functional annotation was conducted to assess differences in gene function among samples. In the M1T1 vs. M0T1 comparison, 1836 DEGs were annotated with biological processes (BPs), cellular components (CCs), and molecular functions (MFs), with 933 (50.82%) for BPs, 132 (7.18%) for CCs, and 771 (42.00%) for MFs. In the M1T2 vs. M0T2 comparison, 3143 DEGs were annotated, with 51.77% for BPs, 6.08% for CCs, and 42.15% for MFs. In the M1T3 vs. M0T3 comparison, 5819 DEGs were annotated, accounting for 53.60%, 5.77%, and 40.63% in BPs, CCs, and MFs, respectively. The ten GO terms with the lowest p-values were selected and displayed as bar graphs (Figure 6). In M1T1 vs. M0T1 (Figure 6A), DEGs were primarily enriched in BP categories such as response to stress, response to biotic stimulus, and defense response; CC categories such as cellular anatomical entity and membrane; and MF categories such as protein binding and copper ion binding. In M1T2 vs. M0T2 (Figure 6B), DEGs were mainly enriched in BP categories such as response to stress, response to biotic stimulus, and defense response; CC categories such as membrane and the intrinsic component of the membrane; and MF categories such as transferase activity, DNA-binding transcription factor activity, and sequence-specific DNA binding. In M1T3 vs. M0T3 (Figure 6C), DEGs were enriched in BP categories such as phosphorylation, oxidation-reduction process, and protein phosphorylation; CC categories such as cellular anatomical entity, membrane, the integral component of the membrane, and the intrinsic component of the membrane; and MF categories involving oxidoreductase activity, protein kinase activity, and phosphotransferase activity, with alcohol group as acceptor. Genes in the three DEG groups were co-enriched in the functions of response to biotic stimulus, cellular anatomical entity, response to stress, and membrane, playing a critical role in lettuce growth and development under magnetized irrigation.

3.4.4. Kegg Enrichment Analysis of DEGs

As shown in Figure 7, the KEGG database was used to analyze the enrichment of DEG metabolic pathways in lettuce following magnetized irrigation from three water sources. In M1T1 vs. M0T1 (Figure 7A), DEGs were primarily enriched in drug metabolism–cytochrome P450, the MAPK signaling pathway—plant, and glutathione metabolism. In M1T2 vs. M0T1 (Figure 7B), DEGs were primarily enriched in brassinosteroid biosynthesis, galactose metabolism, plant hormone signal transduction, and starch and sucrose metabolism. In M1T3 vs. M0T3 (Figure 7C), DEGs were enriched in cysteine and methionine metabolism, plant hormone signal transduction, and glycerolipid metabolism. The MAPK signaling pathway—plant, plant hormone signal transduction, and cysteine and methionine metabolism pathways play key roles in lettuce growth and development. Consequently, DEGs were further mapped to these three metabolic pathways, and the key genes in each were identified. Key genes identified in the MAPK signaling pathway included IRAK1 and IRAK4; in the plant hormone signal transduction pathway, genes such as IAA29, GH3.9, SAUR, and HBP1b were noted; and in the metabolism of cysteine and methionine pathway, key genes included TAT2, BHMT2, CMT2, and AHCY.

4. Discussion

In recent years, magnetized water technology, as an emerging means of agricultural irrigation, has shown potential for improving water quality, crop yield, and WPc [27,28,29,30,31]. Studies have shown that magnetization treatment significantly affects the physicochemical properties of water, including altering the molecular structure of water [32], reducing the surface tension coefficient of water [33], and generating small, active molecular clusters. These smaller molecular clusters exhibit enhanced permeability in cellular metabolism, improved solubility, and consequently lead to increased EC, DO, and pH levels of water [34]. Compared to untreated water, the EC of magnetized water increased by 71.4%, while the pH rose by 7.14% [35]. We found that EC, pH, and DO of fresh, recycled, and saline water increased following magnetization treatment, aligning with previous findings. Physicochemical properties such as EC, pH, and DO in irrigation water significantly influence crop nutrient uptake, quality, and yield. Increasing EC has been found to contribute to biomass accumulation and nitrogen content in lettuce when the EC of irrigation water is in the range of 0.5–2.0 mS/cm; in particular, nitrogen content in lettuce significantly increases in the range of 0.9–1.2 mS/cm [36]. In contrast, leaf growth and yield in lettuce were significantly reduced when the EC of irrigation water exceeded 4.0 dS/m, primarily due to osmotic stress from high salinity [37]. In this study, magnetization of fresh and recycled water increased EC to 0.63 and 0.97 dS/m, respectively, which improved N content and lettuce yield. Meanwhile, the decrease in yield at an EC above 4.0 dS/m for saline water further supported previous findings.
Numerous studies have shown that magnetized irrigation can promote crop growth and development, increase crop yield, and improve quality [38,39,40,41,42]. Magnetized irrigation has been shown to increase the accumulation of trace elements such as nitrogen, phosphorus, and sulfur in plant leaves [39]. The soluble sugar and protein contents of maize were increased by 1.4–38.2% and 11.7–39.6%, respectively, compared with the control after magnetized irrigation [43]. The biomass of rice seedlings under magnetized irrigation increased by 22.4% [44]. Magnetized brackish water was found to enhance crop WPc compared to non-magnetized brackish water [38]. In this study, magnetized irrigation from all three water sources increased mineral element content, soluble protein, soluble sugar, yield, and WPc of lettuce leaves compared to non-magnetized irrigation, which is consistent with previous studies. The observed improvement in crop quality and yield may be attributed to the higher DO levels in magnetized water, facilitating water transport within the plant by promoting root development and mineral uptake, enhancing metabolism, and ultimately increasing aboveground biomass and nutrient accumulation in the crop [45,46].
Magnetic treatment may enhance the efficiency of water and ion uptake by crop root cells by improving irrigation water permeability, which subsequently modulates cellular signaling pathways [47,48]. The magnetic field significantly increased peroxidase (POD) activity in soybean tissues, suggesting that it may improve crop redox homeostasis by enhancing the antioxidant enzyme system to maintain redox balance [49]. Magnetized irrigation up-regulated genes associated with nitrogen uptake (e.g., OsNRT and OsAMT family of genes) in rice, enhancing nutrient uptake efficiency under saline and alkaline environments [50]. In this study, GO enrichment analysis of lettuce irrigated with three magnetized water sources indicated that DEGs were primarily enriched in pathways related to biotic stimulus, cellular anatomical entity, response to stress, and the integral component of the membrane. KEGG enrichment showed that significant DEGs were mainly enriched in the MAPK signaling pathway—plant, plant hormone signal transduction, and cysteine and methionine metabolism. Up-regulated genes were primarily enriched in pathways related to starch and sucrose metabolism, galactose metabolism and amino acid synthesis, metal-ion binding and oxidoreductase activity. These metabolic pathways play important roles in crop growth and development [25,51], starch and sucrose metabolism pathways regulate sugar accumulation [52], galactose metabolism pathway affects carbohydrate conversion [53], amino acid synthesis pathway enhances protein accumulation [54], and metal-ion binding and oxidoreductase activity enhance the stability of crop cell membranes [55], so that magnetized irrigation can promote lettuce yield quality. In this study, key genes in the phytohormone signaling pathway (e.g., IAA29, GH3.9, SAUR, HBP1b) regulated lettuce growth by modulating hormone signaling and perception; while genes in the cysteine and methionine metabolism pathway, such as TAT2 and BHMT2, contributed to the enhancement of lettuce’s antioxidant capacity, which in turn helped it to better adapt to the environment.
Overall, magnetized irrigation optimized nutrient uptake and WPc in lettuce by activating multiple molecular and metabolic pathways, suggesting promising applications in sustainable agriculture. However, as the effects of magnetization are influenced by uncontrollable factors (e.g., magnetic field strength), further detailed studies on its impact across various water sources are needed. In addition, validating the expression patterns of key genes through qRT-PCR will provide a deeper understanding of the long-term effects of magnetized irrigation on crops at the molecular level.

5. Conclusions

Magnetization treatment increased EC, pH, and DO levels in all three water sources, with saline water showing the highest EC, recycled water the highest pH, and fresh water the highest DO. Magnetized irrigation enhanced the contents of N, K, Ca, Mg, soluble sugar, soluble protein, VitC, and WPc in lettuce, with above-ground fresh and dry weights rising by 8.81–9.58% and 4.21–11.42%, respectively. Magnetized fresh water irrigation exhibited the best overall impact, while magnetized recycled water improved lettuce quality and WPc with lower water consumption. The transcriptome analysis revealed that DEGs in lettuce under magnetized irrigation were primarily enriched in the MAPK signaling pathway—plant, phytohormone signaling, and cysteine and methionine metabolism, which may support lettuce development under magnetized irrigation.

Author Contributions

Methodology, X.Y., X.W. and M.Q.; investigation, X.W. and Y.W.; validation, X.Y. and M.Q.; formal analysis, Y.L.; resources, Y.W.; data curation, X.Y. and X.W.; writing—original draft preparation, X.Y.; writing—review and editing, Y.L.; visualization, X.Y.; supervision, X.W., M.Q. and F.S.; project administration, Y.L.; funding acquisition, F.S. All authors have read and agreed to the published version of the manuscript.

Funding

This project was supported by the Yunnan Provincial Science and Technology Department Science and Technology Program (202302AE090020), the Major Achievement Cultivation Program of Beijing Municipal Academy of Agriculture and Forestry, and the Reform and development project of Beijing Academy of Agriculture and Forestry Sciences (Research on the Influence Mechanism and Regulation Method of Ridge Direction Variation on Crop Water Utilization in Solar Greenhouse Planting).

Data Availability Statement

The data used to support the findings of this study are available from the corresponding authors upon request.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Schematic diagram of magnetized water equipment. ((A) Layout of magnetized water device. (B) A schematic view of the magnetizer).
Figure 1. Schematic diagram of magnetized water equipment. ((A) Layout of magnetized water device. (B) A schematic view of the magnetizer).
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Figure 2. Effect of different water sources with magnetized irrigation on the content of mineral elements in lettuce ((A) Lettuce mineral content in 2018. (B) Lettuce mineral content in 2019). Different lowercase letters for the same treatment indicate significant differences at the p < 0.05 level. M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation.
Figure 2. Effect of different water sources with magnetized irrigation on the content of mineral elements in lettuce ((A) Lettuce mineral content in 2018. (B) Lettuce mineral content in 2019). Different lowercase letters for the same treatment indicate significant differences at the p < 0.05 level. M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation.
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Figure 3. Analysis of gene expression in different irrigation water sources under magnetization and non-magnetization treatments ((A) Fragments per kilobase of exon model per million-mapped-fragment (FPKM) values of samples. (B) Principal component analysis (PCA) of sample expression. (C) Similarity cluster analysis of samples). M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation.
Figure 3. Analysis of gene expression in different irrigation water sources under magnetization and non-magnetization treatments ((A) Fragments per kilobase of exon model per million-mapped-fragment (FPKM) values of samples. (B) Principal component analysis (PCA) of sample expression. (C) Similarity cluster analysis of samples). M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation.
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Figure 4. Number of differentially expressed genes (DEGs) in each comparison group (red represents up-regulated DEGs, green represents down-regulated DEGs). M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation.
Figure 4. Number of differentially expressed genes (DEGs) in each comparison group (red represents up-regulated DEGs, green represents down-regulated DEGs). M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation.
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Figure 5. Volcano plot of differentially expressed genes (DEGs) in the comparison groups of fresh water, recycled water and saline water before and after magnetized water irrigation. “Up” represents up0-regulated DEGs, “Down” represents down-regulated DEGs, and “insignificant” represents DEGs of no significance. ((A) M1T1 vs. M0T1. (B) M1T2 vs. M0T2. (C) M1T3 vs. M0T3). M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation. The dashed lines on both sides of the Y-axis indicate Log2(Fold Change) = ± 1, which is the threshold for significant expression of difference. Data points beyond this range are considered as significantly up-regulated (right) or significantly down-regulated (left). The dotted line above the X-axis indicates p = 0.05, the data points above the dotted line are statistically significant.
Figure 5. Volcano plot of differentially expressed genes (DEGs) in the comparison groups of fresh water, recycled water and saline water before and after magnetized water irrigation. “Up” represents up0-regulated DEGs, “Down” represents down-regulated DEGs, and “insignificant” represents DEGs of no significance. ((A) M1T1 vs. M0T1. (B) M1T2 vs. M0T2. (C) M1T3 vs. M0T3). M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation. The dashed lines on both sides of the Y-axis indicate Log2(Fold Change) = ± 1, which is the threshold for significant expression of difference. Data points beyond this range are considered as significantly up-regulated (right) or significantly down-regulated (left). The dotted line above the X-axis indicates p = 0.05, the data points above the dotted line are statistically significant.
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Figure 6. Gene ontology (GO) classification and distribution of GO-annotated genes. ((A) M1T1 vs. M0T1. (B) M1T2 vs. M0T2. (C) M1T3 vs. M0T3). M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation.
Figure 6. Gene ontology (GO) classification and distribution of GO-annotated genes. ((A) M1T1 vs. M0T1. (B) M1T2 vs. M0T2. (C) M1T3 vs. M0T3). M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation.
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Figure 7. Kyoto encyclopedia of genes and genomes (KEGG) pathway enrichment analysis of DEGs in response to different treatments. ((A) M1T1 vs. M0T1. (B) M1T2 vs. M0T2. (C) M1T3 vs. M0T3). M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation.
Figure 7. Kyoto encyclopedia of genes and genomes (KEGG) pathway enrichment analysis of DEGs in response to different treatments. ((A) M1T1 vs. M0T1. (B) M1T2 vs. M0T2. (C) M1T3 vs. M0T3). M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation.
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Table 1. Basic physical properties of soil.
Table 1. Basic physical properties of soil.
Particle Size DistributionBulk DensityField CapacitySaturation Moisture ContentEC
Sand/%Silt/%Clay/%g/cm3%%mS/m
53.162422.841.4430.59487.81
Table 2. Nutrient contents in the soil where the experiment was conducted.
Table 2. Nutrient contents in the soil where the experiment was conducted.
Total Nitrogen
g/kg		Ammonium Nitrogen
mg/kg		Nitrate Nitrogen
mg/kg		Available Phosphorus
mg/kg		Available Potassium
mg/kg
1.2614.77.2414.2138
Table 3. Effect of magnetized treatment on the water quality of different sources. Different lowercase letters for the same treatment indicate significant differences at the p < 0.05 level. EC: electrical conductivity; DO: dissolved oxygen. M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation.
Table 3. Effect of magnetized treatment on the water quality of different sources. Different lowercase letters for the same treatment indicate significant differences at the p < 0.05 level. EC: electrical conductivity; DO: dissolved oxygen. M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation.
TreatmentEC
dS/m		pHDO
M0T10.62 ± 0.07c7.43 ± 0.13d8.61 ± 0.16bc
M0T20.96 ± 0.04b7.89 ± 0.04c8.15 ± 0.50d
M0T34.36 ± 0.06a7.52 ± 0.14d8.57 ± 0.05c
M1T10.63 ± 0.07c7.95 ± 0.07bc9.56 ± 0.08a
M1T20.97 ± 0.04b8.34 ± 0.04a8.96 ± 0.11b
M1T34.39 ± 0.06a8.01 ± 0.06b9.45 ± 0.07a
Table 4. Analysis of variance (ANOVA) of magnetization and irrigation water source on the electrical conductivity (EC), pH, and dissolved oxygen (DO) of different water sources. The data in the table are the F-values of different factors, * indicates p < 0.05, ** indicates p < 0.01, and ns indicates that the effect of factors is not significant. M: magnetization treatment; T: irrigation water source.
Table 4. Analysis of variance (ANOVA) of magnetization and irrigation water source on the electrical conductivity (EC), pH, and dissolved oxygen (DO) of different water sources. The data in the table are the F-values of different factors, * indicates p < 0.05, ** indicates p < 0.01, and ns indicates that the effect of factors is not significant. M: magnetization treatment; T: irrigation water source.
FactorECpHDO
M1.73 ns278.62 **81.10 **
T27,680.09 **80.05 **11.39 **
M*T0.17 ns0.53 ns0.19 ns
Table 5. Analysis of variance (ANOVA) of the effects of magnetization and irrigation water sources on mineral element content of lettuce. M: magnetization treatment; T: irrigation water source. The data in the table are the F-values of different factors, * indicates p < 0.05, ** indicates p < 0.01, and ns indicates that the effect of factors is not significant.
Table 5. Analysis of variance (ANOVA) of the effects of magnetization and irrigation water sources on mineral element content of lettuce. M: magnetization treatment; T: irrigation water source. The data in the table are the F-values of different factors, * indicates p < 0.05, ** indicates p < 0.01, and ns indicates that the effect of factors is not significant.
YearFactorNPKCaMg
2018M19.63 **1.20 ns7.33 *7.45 *1.18 ns
T8.30 **10.56 **2.71 ns2.64 ns8.58 **
M*T0.75 ns2.13 ns1.09 ns0.11 ns0.10 ns
2019M11.00 **2.38 ns8.43 *6.71 *9.42 *
T9.74 **7.57 *1.26 ns7.40 *5.15 *
M*T0.47 ns3.55 ns0.32 ns0.53 ns0.20 ns
Table 6. Effect of magnetized water irrigation on lettuce quality, yield, and water productivity (WPc) under different irrigation water sources. Different lowercase letters for the same treatment indicate significant differences at the p < 0.05 level. M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation.
Table 6. Effect of magnetized water irrigation on lettuce quality, yield, and water productivity (WPc) under different irrigation water sources. Different lowercase letters for the same treatment indicate significant differences at the p < 0.05 level. M0T1: fresh water irrigation; M0T2: recycled water irrigation; M0T3: saline water irrigation; M1T1: magnetized fresh water irrigation; M1T2: magnetized recycled water irrigation; M1T3: magnetized saline water irrigation.
YearTreatmentSoluble
Protein		Soluble
Sugar		VitCFresh
Weight		Dry
Weight		Water
Consumption		WPc
mg/gmg/gmg/kgg/plantg/plantg/potkg/m3
2018M0T12.02 ± 0.15b21.50 ± 0.85bc157.00 ± 10.30cd345.45 ± 20.50b20.24 ± 1.85bc7.39 ± 0.20a46.86 ± 2.10bc
M0T21.78 ± 0.20c18.67 ± 0.89c148.10 ± 8.45d340.78 ± 18.80b19.54 ± 1.55bc7.18 ± 0.18ab47.53 ± 2.15b
M0T31.69 ± 0.17c22.50 ± 1.10b161.67 ± 9.88cd289.45 ± 15.20c17.25 ± 1.35c6.76 ± 0.25c42.45 ± 1.98d
M1T12.40 ± 0.18a26.80 ± 1.05a205.00 ± 11.50a379.13 ± 22.00a21.99 ± 1.90a7.23 ± 0.30a52.50 ± 2.25a
M1T22.28 ± 0.12a24.00 ± 0.95ab172.00 ± 9.00bc366.22 ± 21.50a20.85 ± 1.80ab7.06 ± 0.28b51.88 ± 2.20a
M1T31.90 ± 0.14bc26.40 ± 1.20a180.00 ± 10.55b302.39 ± 16.40c17.89 ± 1.45c6.68 ± 0.26c45.28 ± 2.00cd
2019M0T11.83 ± 0.10bc24.17 ± 1.07c164.67 ± 9.24b362.66 ± 28.30b23.71 ± 1.85abc8.22 ± 0.35a44.24 ± 2.80b
M0T21.72 ± 0.08c23.77 ± 0.88c170.33 ± 10.12ab353.21 ± 12.04b22.05 ± 1.09bcd8.16 ± 0.32a43.35 ± 2.07b
M0T31.80 ± 0.09c28.63 ± 1.15ab191.00 ± 11.07a297.37 ± 16.76c19.88 ± 0.73d7.42 ± 0.29b40.13 ± 1.66c
M1T12.30 ± 0.11a28.07 ± 0.98b178.00 ± 10.20ab396.82 ± 21.74a26.10 ± 0.86a8.47 ± 0.40a46.93 ± 2.41a
M1T22.07 ± 0.09ab26.73 ± 1.20bc176.00 ± 9.35ab389.06 ± 24.65a25.61 ± 1.22ab8.05 ± 0.35a48.40 ± 3.23a
M1T31.91 ± 0.12bc31.37 ± 1.25a185.33 ± 10.85ab309.10 ± 10.55c21.56 ± 0.64cd7.34 ± 0.28b42.15 ± 1.05bc
Table 7. Analysis of variance (ANOVA) of magnetization, and irrigation water source on quality, yield, and water productivity (WPc) of lettuce. M: magnetization treatment; T: irrigation water source. The data in the table are the F-values of different factors, * indicates p < 0.05, ** indicates p < 0.01, and ns indicates that the effect of factors is not significant.
Table 7. Analysis of variance (ANOVA) of magnetization, and irrigation water source on quality, yield, and water productivity (WPc) of lettuce. M: magnetization treatment; T: irrigation water source. The data in the table are the F-values of different factors, * indicates p < 0.05, ** indicates p < 0.01, and ns indicates that the effect of factors is not significant.
YearFactorSoluble ProteinSoluble SugarVitCFresh WeightDry WeightWater
Consumption		WPc
2018M38.39 **39.52 **40.38 **32.89 **8.85 *3.14 ns30.59 **
T16.31 **6.64 *6.53 *98.73 **26.10 **33.92 **25.10 **
M*T2.05 ns0.37 ns3.70 ns2.07 ns0.60 ns0.02 ns1.61 ns
2019M24.49 **16.8 **0.75 ns55.59 **7.91 *0.04 ns28.63 **
T4.4587 *14.01 *4.34 *175.38 **7.70 **29.44 **25.45 **
M*T2.91 ns0.21 ns1.05 ns4.52 *0.37 ns1.16 ns2.29 ns
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Yao, X.; Wang, X.; Qu, M.; Wei, Y.; Shan, F.; Li, Y. Combined Effects of Magnetized Irrigation and Water Source on Italian Lettuce (Lactuca sativa L. var. ramosa Hort.) Growth and Gene Expression. Agronomy 2024, 14, 2621. https://doi.org/10.3390/agronomy14112621

AMA Style

Yao X, Wang X, Qu M, Wei Y, Shan F, Li Y. Combined Effects of Magnetized Irrigation and Water Source on Italian Lettuce (Lactuca sativa L. var. ramosa Hort.) Growth and Gene Expression. Agronomy. 2024; 14(11):2621. https://doi.org/10.3390/agronomy14112621

Chicago/Turabian Style

Yao, Xueying, Xiaofan Wang, Mingshan Qu, Yibo Wei, Feifei Shan, and Youli Li. 2024. "Combined Effects of Magnetized Irrigation and Water Source on Italian Lettuce (Lactuca sativa L. var. ramosa Hort.) Growth and Gene Expression" Agronomy 14, no. 11: 2621. https://doi.org/10.3390/agronomy14112621

APA Style

Yao, X., Wang, X., Qu, M., Wei, Y., Shan, F., & Li, Y. (2024). Combined Effects of Magnetized Irrigation and Water Source on Italian Lettuce (Lactuca sativa L. var. ramosa Hort.) Growth and Gene Expression. Agronomy, 14(11), 2621. https://doi.org/10.3390/agronomy14112621

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