Abstract
The surge in demand for ornamental crops necessitates a more efficient and accurate fertilization regimen, attributed to their high nutritional requirements and vigorous growth. However, there is limited research exploring the response of Epipremnum aureum on Foliar-applied amino acid biostimulants, which can potentially improve the growth and antioxidant properties of these Epipremnum aureum. To address this gap, an indoor pot experiment was conducted, encompassing six treatments that varied in the concentration of applied amino acid biostimulants: 0.00% (T0), 0.04% (T1), 0.06% (T2), 0.08% (T3), 0.10% (T4), and 0.20% (T5). The results showed that the 0.08% concentration significantly increased peroxidase activity by 72.76%. Moreover, the 0.10% concentration increased chlorophyll content, catalase activity, dry mass, and total antioxidant capacity by 44.41%, 69.55%, 2.04-fold and 3.38-fold, respectively. Additionally, the 0.20% concentration significantly increased soluble sugar content by 52.32%. In conclusion, leaf-applied amino acid biostimulants significantly improved the yield and quality of Epipremnum aureum, with the optimal application concentration being 0.10%. These amino acid biostimulants, serving as efficient and non-toxic fertilizers, exhibit promising prospects for widespread application in agricultural production.
REVIEWING EDITOR:
Introduction
Epipremnum aureum is one of the most common ornamental crops available, which can purify the air by metabolically removing various toxic pollutants and plays a pivotal role in creating a conducive living environment for humans and upholding ecological equilibrium (Ravi et al., Citation2021; Zuo et al., Citation2021). Over recent years, the global ornamental crop industry has witnessed significant growth owing to the escalating demand for landscaping, indoor embellishment, and related purposes (Hajihashemi & Omolbanin, Citation2023). Facilitating the growth and maturation of Epipremnum aureum necessitates multiple applications of fertilizers to ensure an adequate nutrient supply, promoting robust plant development and enhancing both yield and quality (Mobli et al., Citation2022). The fertilization regimen for Epipremnum aureum should adhere to the principles of precision with multiple applications because over-fertilizing can cause seedling burning and excessive stem elongation. In contrast, inadequate fertilization may result in frail branches, chlorotic foliage, and heightened vulnerability to pests and diseases. Thus, it is of great practical significance to discover efficient biostimulants and fertilization strategies to enhance the robust development of Epipremnum aureum, ultimately maximizing economic return.
The foliar application of amino acids biostimulants, where amino acids serve as the primary active ingredients, emerges as a promising strategy for precisely fulfilling the fertilization requirements of Epipremnum aureum. Moreover, amino acids, fundamental protein constituents, are indispensable for plant growth, significantly enhancing crop growth and optimizing nutrient utilization efficiency (Halpern, Bar-Tal & Ofek, 2015; Teixeira et al., Citation2017). Additionally, they play a vital role in regulating photosynthesis and resisting environmental stress, thereby improving crop quality (Al-Karaki & Othman, Citation2023; Buchanan et al., Citation2000; Mohamad et al., Citation2022). More specifically, certain amino acids demonstrate distinct benefits. Leucine and isoleucine improve crop resistance to salt stress and promote meristem growth (Dierk & John, Citation1985). Aspartic acid promotes protein synthesis and offers nitrogen support during periods of crop stress (Lei et al., Citation2022). Glutamic acid stands out as the primary amino acid for nitrogen uptake in plants, fostering leaf photosynthesis and augmenting chlorophyll biosynthesis (Yoneyama & Suzuki, Citation2020). Arginine serves as a precursor for synthesizing the endogenous plant hormone polyamine, thereby contributing to enhanced root development (Silveira et al., Citation2021).
The extensive cultivation of ornamental crops makes foliar application of amino acid biostimulants viable. For instance, research indicates that applying plant-growth biostimulants containing amino acids can elevate chlorophyll levels, nitrogen content, and total sugar content in citrus crops (Khan et al., Citation2022). Furthermore, the foliar application of a composite solution of amino acids, such as proline, valine, and alanine, can potentially enhance nutrient utilization efficiency, crop yield, and fruit quality in fava wheat. This approach also results in heightened leaf nutrition (i.e. nitrogen, phosphorus, and potassium) levels and improved fruit yield and quality in beans, as corroborated by studies (Ali et al., Citation2022; Taimur et al., Citation2018). Similarly, the foliar application of aspartic acid as a plant growth biostimulant has proven effective in elevating both the yield and nutrient content of tomatoes (Sadak et al., Citation2023). Moreover, γ-Aminobutyric acid enhances the photosynthetic capacity and antioxidant enzyme activity, reduces leaf malondialdehyde content and conductivity, ameliorates cellular damage induced by NaCl, and improves salt tolerance in wheat seedlings (Li et al., Citation2016).
The research on amino acids centers primarily on food crops, certain vegetables, and fruits, with comparatively less attention on ornamental crops. Foliar application of amino acids is a direct delivery of amino acids to the target through the stomata and cell walls on the surface of the leaf, which can rapidly absorb and transport nutrients. This method may prove more effective for ornamental crops, particularly those with larger leaf areas. Consequently, the present study was conducted in pots with an ornamental crop, Epipremnum aureum, to systematically investigate the effects of foliar-applied amino acid biostimulants on such crops. The objective was to explore their potential to enhance ornamental crop quality and fortify plant resistance mechanisms. Through a methodical comparative analysis of the growth and antioxidant properties of ornamental crops subjected to varying concentrations of foliar-applied amino acid biostimulants, the study aimed to determine the optimal concentration for enhancing ornamental crop attributes through amino acid biostimulants foliar application.
Materials and methods
Experimental design and treatment applications
The experiment involved an indoor potted plant trial. Epipremnum aureum was randomly assigned to 6 groups receiving increased concentrations of amino acid biostimulants: 0.00% (T0), 0.04% (T1), 0.06% (T2), 0.08% (T3), 0.10% (T4), and 0.20% (T5) for 90 d, with five replicates allocated to each group. During the rapid growth period, the indoor environment was maintained within a temperature range of 15 °C–20 °C and a relative humidity of 50%–70%. A dosage of 150 mL of amino acid biostimulants was sprayed on the foliage every seven days. No other fertilizers were applied during the cultivation period. At the end of the study, plant samples were collected to determine growth, physiology, and antioxidant enzyme activities.
Materials source
Plant material
The variety chosen for this experiment was the green leaf Epipremnum aureum, purchased from Chuzhou Green Flower Maintenance Company, China. The plants were selected for potting within 30 d of planting and exhibited consistent growth characteristics throughout cultivation.
Plant culture substrates
The plant culture substrates used in the experiment were purchased from Hefei Green Fertilizer Agricultural Science and Technology Co., Ltd. It consisted of a blend of perlite, coconut shell, peat, slow-release fertilizer, pine scale, and crushed coconut husk. The physicochemical properties of the plant culture substrates are presented in .
Table 1. Basic physical and chemical properties of plant culture substrates.
Amino acid biostimulants
The amino acid biostimulants utilized in this experiment were obtained from an aspartic acid biological fermentation solution. The composition and content of the amino acid biostimulants were detected by high-performance liquid chromatography (HPLC) (LC-20AB, Shimadzu, Japan) and quadrupole-coupled plasma mass spectrometry (ICP-MS) (ICAP Q, Thermo Fisher Scientific, American). The results are shown in and .
Table 2. Amino acid type and content.
Table 3. Element type and content.
Plant growth measurements
Petiole length
Petiole length was measured as the linear distance from the stem base to the leaf blade, selected from the second fully expanded leaf, and length was expressed in centimeters (cm).
Leaf area
Leaf area was calculated as an average of the first, third, and fifth leaves from the top of the greens. The area was expressed in square centimeters (cm2).
Conductivity
Leaf conductivity was determined using a conductivity meter (FE30K, Mettler Toledo, Switzerland) and expressed as a percentage.
Total chlorophyll
Total chlorophyll content was quantified spectrophotometrically (Gregor & Marsálek, Citation2004) by a full-wavelength microplate reader (Multiskan Go, Thermo Fisher Scientific, American). The total content was expressed as milligrams per gram (mg·g−1).
Biomass
The plant stems and leaves were collected as aboveground samples, and the plant roots were collected as belowground samples. The fresh weight of the samples was directly recorded. The dried weight of the samples was recorded by drying at 110 °C–120 °C for 10–20 minutes and subsequently at 60 °C–70 °C until a constant weight was achieved. The weight was expressed in grams (g).
Plant physiology and antioxidant enzyme activity assay
Physiology
The soluble sugars content (WSS) was determined using anthrone colorimetry (Michel et al., Citation1956) and expressed as milligrams per gram (mg·g−1).
Malondialdehyde (MDA) content was measured by the thiobarbituric acid (TBA) method (Heath & Packer, Citation1968) with a slight modification and expressed as nanomoles per gram (nmol·g−1).
The total protein concentration (TP) was measured by slightly modifying the Caumas Brilliant Blue method (Löffler & Kunze, Citation1989) and expressed as grams per liter (g·L−1).
Antioxidant enzyme activity
Total antioxidant capacity (T-AOC), total superoxide dismutase (T-SOD), catalase (CAT), and peroxidase (POD) activities were measured by kits (A015-1, A001-1, A007-1-1, A084-3-1), all purchased from Nanjing Jiancheng Bioengineering Institute. Enzyme activities were expressed as units per gram fresh weight (U·g−1 FW).
Data analysis
The experimental data were analyzed using Excel 2019. SPSS 22.0 was used for one-way ANOVA and significance test (Duncan’s method). The results were expressed as the mean and standard error of the mean (SEM), and P < 0.05 indicated significant differences.
Results and discussion
Growth of Epipremnum aureum
The results demonstrate that foliar-applied amino acid biostimulants significantly enhanced the growth of Epipremnum aureum. As shown in , the petiole length peaked at 0.10% concentration, reaching 15.11 cm (P < 0.05), which increased by 15.97% compared with the control. The chlorophyll content achieved its highest level at 0.10% concentration, measuring 14.10 mg·L−1 (P < 0.05), marking a 44.41% rise over the control. The leaf area peaked at 0.20% concentration, reaching 46.78 cm2 (P < 0.05), increased by 18.02% compared with the control. Additionally, conductivity reached the lowest at 0.10% concentration, measuring 7.07% (P < 0.05), which decreased by 46.33% compared with the control.
Table 4. The Impact of Amino Acid Biostimulants on the Growth of Epipremnum aureum.
In this study, the amino acid content was higher in the 0.20% concentration of the biostimulant than in the 0.10% concentration. However, the petiole length and chlorophyll content were reduced, presumably due to the different amino acid contents resulting in different morphological responses. Similarly, Khan et al. (Citation2019) found that higher concentrations inhibited crop growth. Additionally, high conductivity values affect water transport from the substrate to the plant by reducing osmotic pressure and limiting crop growth (Belda et al., Citation2013). Studies indicated that chlorophyll content in leaves reflects tissue toxicity resulting from ion accumulation, and the amount of reactive oxygen species synthesized by chloroplasts reduced with the chlorophyll content decrease (Khosravinejad et al., 2018; Gilmore & Ball, Citation2000). Green leaf area increases with increasing amino acid concentration, probably because amino acids, as a nitrogen source, provide the required nutrients to green leaves, making them larger and darker green (Ning et al., Citation2018). Similar effects have been found in the application of amino acids to mung beans, broccoli, onions, and other crops, promoting crop growth and improved yield and fruit quality (Bouranis et al., Citation2023; Mobini et al., Citation2014; Ramyar et al., Citation2022). Consequently, optimal amino acid application during the cultivation and management of ornamental crops can improve productivity and ornamental value.
Biomass of Epipremnum aureum
The increased application of amino acid biostimulants demonstrated an increase in the weight of both aboveground and underground parts of Epipremnum aureum, aligning with findings from Kausar et al. (Citation2023) study on spinach. As shown in , this study depicted its peak values at an amino acid concentration of 0.10%, with the maximum aboveground fresh weight recorded was 329.57 g (P < 0.05), increased by 2.64-fold compared with the control, and the aboveground dry weight measured 57.63 g (P < 0.05), marking a 1.51-fold rise over the control. In the underground components, the fresh weight reached 128.40 g (P < 0.05), increased by 51.13% compared with the control, and the dry weight was 14.96 g (P < 0.05), marking a 62.89% rise over the control.
Figure 1. The Impact of Amino Acid Biostimulants on the Growth of Epipremnum aureum.
(The error is the standard deviation (n = 5), and the same letter after the error indicates no significant difference at the 0.05 probability level), (A): aboveground fresh weight, (B) aboveground dry weight, (C) underground fresh weight, (D) underground dry weight.
The relationship between underground growth and biomass has been consistently highlighted in various studies (Mendoza-Pérez & Figueroa-Castro, Citation2023). The study of Al-Janabi et al. (Citation2021) indicated that foliar application of amino acids increased maize growth and yield by facilitating nutrient uptake, including nitrogen, phosphorus, potassium, and micronutrients. The study of Haghighi et al. (Citation2022) demonstrated that the application of amino acid biostimulants stimulated root formation, enhancing the growth of aboveground plant parts. In this study, the biomass was raised with concentration increments when amino acid concentrations were below 0.10%. This increased trend suggests that increased amino acid application promotes nutrient absorption by plant roots, fostering plant production and development while enhancing the quality of fresh and dry matter (Colla et al., Citation2017; He et al., Citation2020). However, when amino acid concentrations surpassed 0.10%, the biomass of Epipremnum aureum exhibited a decline. This decline is hypothesized to stem from excessively high amino acid concentrations blocking the respiration rate of plant roots and leaves, resulting in decreased biomass (Rosiane et al., Citation2011). Therefore, optimal amino acid application can enhance plant photosynthetic efficiency, promote carbon conversion, and augment plant biomass.
Antioxidant properties of Epipremnum aureum
These findings showed the positive impact of including amino acid biostimulants on the biochemical characteristics of Epipremnum aureum, particularly in enhancing its antioxidant capacity. As shown in , T-AOC activity peaked at 0.10% concentration, reaching 38.05 U·g−1 FW (P < 0.05), which increased by 3.38-fold compared with the control. The WSS content achieved its highest level at 0.20% concentration, measuring 9.48 mg·g−1 (P < 0.05), marking a 52.32% rise over the control. Additionally, MDA content reached the lowest at 0.10% concentration, measuring 22.68 nmol·g−1 (P < 0.05), which decreased by 23.97% compared with the control. The total protein content was not significant.
Figure 2. The effect of amino acid biostimulants on the antioxidant properties of Epipremnum aureum.
(The error bars represent the standard deviation (n = 5), and the same letters on the error bars indicate no significant difference at the 0.05 probability level.) T-AOC: total antioxidant capacity (A), WSS: soluble sugar (B), MDA: malondialdehyde (C), TP: total protein (D).
The application of amino acid biostimulants exhibited an increase in WSS content and a decrease in MDA content with in the treatment group compared to the control group. Bakpa et al. (Citation2021) conducted a study on pepper and demonstrated that 1.8 kg of amino acid water-soluble fertilizer foliar-applied improved WSS content with enhanced physiological characteristics and fruit quality. Similarly, Jiang et al. (Citation2020) explored the effects of amino acid foliar fertilizer on maize, which found decreased MDA content and increased antioxidant enzyme activity. The study of Wang et al. (Citation2009) and Hebat-Allah et al. (Citation2019) indicated that exogenous amino acid application heightened the antioxidant enzyme activity in sugar beet, enhanced free radical scavenging ability. These studies propose that the elevation in WSS content may serve as an osmoregulatory mechanism to protect cells from injury (Tóth et al., Citation2022). Moreover, amino acids contribute to reducing the toxic effects of MDA and hydroxyl free radicals on crops by enhancing cell membrane stability and antioxidant capacity (Li et al., Citation2022). These effects collectively enhanced crop yield and quality while improving the antioxidant capacity of Epipremnum aureum.
Antioxidative enzyme activity of Epipremnum aureum
These findings indicate that adding amino acid biostimulants enhanced the antioxidant enzyme activity of Epipremnum aureum. As shown in , the T-SOD activity peaked at 0.10% concentration, reaching 137.22 U·g−1 FW (P < 0.05), which increased by 27.58% compared with the control. Additionally, CAT activity achieved its highest level at 0.10% concentration, measuring 25.60 U·g−1 FW (P < 0.05), marking a 69.55% rise over the control. The POD activity peaked at 0.08% concentration, reaching 92.27 U·g−1 FW (P < 0.05), increased by 72.76% compared with the control.
Figure 3. Antioxidant enzyme activity of Epipremnum aureum.
(The error bars represent the standard deviation (n = 5), and the same letters on the error bars indicate no significant difference at the 0.05 probability level.) T-SOD: total superoxide dismutase (A), CAT: catalase (B), POD: peroxidase (C).
Studies have consistently indicated that adding amino acids, whether individually or in combination with foliar-applied, enhanced the activity of antioxidant enzymes in crops (Tatjana et al., Citation2015; Teixeira et al., Citation2017). In this experiment, the application of amino acid biostimulants significantly improved the activities of T-SOD, CAT, and POD within the treatment group. Ji et al. (Citation2014) observed a substantial enhancement in the activity of antioxidant enzymes in wheat when supplemented with irrigated amino acid fertilizer during its growth period. Similarly, Man et al. (Citation2017) found that appropriate concentrations of aspartic acid and glutamic acid significantly increased T-SOD and CAT activities in buckwheat leaves. These effects can be attributed to the protective functions of specific enzymes. Total superoxide dismutase preserved plant membrane structure (Woith et al., Citation2017), catalase eliminated excess hydrogen peroxide (Galina et al., Citation2022), and peroxidase mitigated cell membrane damage (Zhang et al., Citation2022). Amino acid application stimulates these enzyme activities, reducing reactive oxygen species damage to biological macromolecules and enhancing overall antioxidant enzyme activity.
Additionally, heightened T-SOD, CAT, and POD activities in plants have been linked to increased tolerance to formaldehyde and improved formaldehyde removal rates (Qiao et al., Citation2023). Liang et al. (Citation2019) demonstrated the essential role of enzymatic reactions in indoor harmful gas decomposition by plants. Consequently, the substantial increase in antioxidant enzyme activity observed in this experiment could effectively facilitate plant redox reactions, enhancing their stress resistance.
Conclusion
The foliar application of amino acid biostimulants proves beneficial in enhancing nutrient absorption and elevating both yield and quality in Epipremnum aureum. The results showed that the 0.08% treatment increased the peroxidase activity by 72.76% compared with the control. The 0.10% treatment increased the leaf petiole length by 15.97%, chlorophyll content by 44.41%, total superoxide dismutase activity by 27.58%, catalase activity by 69.55%, dry mass by 2.04-fold and antioxidant capacity by 3.38-fold. The 0.20% treatment increased leaf area by 18.02% and soluble sugar content by 52.32%. In this case, the 0.10% treatment demonstrated the most favorable effects. The results serve as a valuable reference for applying amino acid biostimulants in ornamental crops and establish a foundational framework for further exploration into the action mechanism of amino acids.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Additional information
Funding
Notes on contributors
Jiarong Cheng
Jiarong Cheng is a postgraduate majoring in Resource Utilization and Plant Protection at Anhui Science and Technology University.
Jiahui Cheng
Jiahui Cheng is a postgraduate majoring in agronomy and seed industry, and she works on the research on the effects of high-yield and efficient cultivation practices on crop production.
Ruifeng Sun
Ruifeng Sun is an undergraduate majoring in environmental engineering, and he works on the research on the impact of the environment on plants.
Shengfei Cao
Shengfei Cao is a product development technician in the Technology and Quality Department, and he works on the research on the plant biostimulants.
Xiang Wang
Xiang Wang Ph.D., works on the research on plant nutrition regulation. Compared to other fertilizers, amino acid biostimulants allow for more accurate control of nutrient content, improving crop yield and quality and reducing pollution of the soil and environment. In this experiment, we revealed the effect of foliar-applied amino acid biostimulants on Epipremnum aureum, which exhibits promising prospects for widespread application in agricultural production.
Hongxing Yang
Hongxing Yang, Ph.D. from Nanjing Agricultural University, majoring in microbiology, works in the Key Laboratory of Bio-organic Fertilizer Creation of the Ministry of Agriculture, College of Resources and Environment, Anhui Science and Technology University. Long-term engaged in plant nutrition and soil microbial research. Published more than 20 related research articles in Journal of Hazardous Materials, Journal of the Science of Food and Agriculture, Applied and Environmental Microbiology, and other journals. Xiang Wang, Ph.D., works on the research on plant nutrition regulation.
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