A water deficit can significantly limit the sustainable production of plants, resulting in reduced growth, development,and flowering. The use of biostimulants improves plant stability and promotes growth under low-irrigation conditions.
Introduction
Tuberose(Polianthes tuberose L.)is a bulbous plant originating from Mexico.It is highly valued for its fragrant,long-lasting flowers,which are widely used as popular scents in the cut flower industry. Additionally, tuberose is widely cultivated for its essential oils, which are highly prized in the perfume industry, and it is also a popular ornamental plant, blooming in the spring and early autumn. Its unique fragrance and versatility have made tuberose a sought-after crop for both commercial and horticultural purposes.
A water deficit is an abiotic factor that affects the growth and postharvest quality of cut flowers. Previous studies have demonstrated that water limitation or water stress can have a profound impact on the quantity and quality of cut flower yields, as well as their ornamental value. Specifically, water deficits can negatively affect the flowering process in many plant species, including tuberose, by reducing the formation of new flowers and altering the overall flowering pattern.
To alleviate the negative impacts of water deficits on floricultural products, various compounds such as plant hormones, biostimulants, and chemical nutrients are used. Among these, biostimulants are a promising agroecological practice that involves the utilization of bioactive compounds from ethnomedicinal plants. These compounds are gaining popularity for their environmentally friendly and cost-effective production methods. However, despite their potential benefits, there is a lack of information on the natural biostimulants that can be extracted from plants. Further research is needed to explore the efficacy of these biostimulants in mitigating the negative impacts of water deficit on floricultural products.
Seaweed Extract is a potent biostimulant useful for the mitigation of the effects of water stress on plant growth and productivity. Seaweed Extract enables the breakdown of unusable sugars in the plant through increasing the concentration of chlorophyll in plant leaves and amylase enzyme in plant organs, thereby promoting plant growth and development. The application of Seaweed Extract has been shown to have numerous benefits for plant growth and productivity, including increased plant height, leaf number, and root growth,as well as accelerated flowering time, increased fruit formation, and delayed leaf senescence. Moreover, Seaweed Extract has been found to improve plant resistance to environmental stresses such as drought, salinity,and temperature. Another biofertilizer that has gained attention in recent years is the endophytic arbuscular mycorrhizal fungi(AMF), which forms a symbiotic relationship with plants to enhance their growth and stress tolerance. AMF interacts with plants by increasing the central carbon metabolism flux among the TCA cycle, GABA shunt, and glyoxylic pathway. This interaction not only promotes plant growth but also reduces oxidative damage in stress conditions and alters the diversity and structure of root and soil microbial communities in plant bed cultures. Furthermore, in drought conditions,the symbiosis between plants and mycorrhiza can stimulate growth by generat-ing phytohormones and providing essential nutrients. This highlights the potential of AMF as a biofertilizer to improve plant growth and productivity,particularly under stressful environmental conditions.
We hypothesize that biostimulants play a significant role in improving the quantity and quality of indices of the bulbs, stems, and cut flowers of tuberosa under water-deficit conditions,and that biostimulants can mitigate the negative effects of water deficits on this species. However, there is a lack of information on the responses of tuberosa to biostimulators such as Seaweed Extract and mycorrhiza symbiosis under water-deficit conditions. Therefore, this study was conducted to investigate the effects of biostimulators on morphological and physiological changes in tuberose plants grown under water-deficit conditions. This study aims to provide a theoretical basis for understanding the responses of tuberose plants to water deficits that can be applied to optimize growth and maximize the yield of cut flowers.
Material and Methods
2.1Experimental Area and Condition
There was a relative humidity of 65–75% and there were mean minimum and maximum temperatures of 22 and 26℃, respectively.The substrate used in this experiment constituted a mixture of garden soil, sand, and completely decayed manure in a ratio of 2:1:1. The initial composition of the substrate is shown in Table1.
| Variable | Porosity | Bulk Density (g·cm−3) | pH | E.C. (S·m−1) | C/N Ratio | N (g·kg−1) | P (g·kg−1) | K (g·kg−1) |
| Substrate | 45.06 | 1.31 | 6.71 | 2.63 | 9.10 | 4.11 | 3.91 | 4.33 |
2.2Experimental Material,Treatments and Design
The experimental materials were improved bulbs of tuberose. The experiment involved a a 4×4 factorial arrangement laid out in a completely randomized design. We used three replications consisting of three pots per plot,with one plant per pot. The 16 treatment combinations were obtained in relation to two factors:factor one is the water deficit(WD)with four levels including WD0(100%field capacity; FC), WD1(80%FC), WD2(60%FC), and WD3(40%FC). These applied from the three-leaf stage for an 8-week period until the first floret opened on the first plant. These were applied based on the daily weight of the pots. The levels of the other factor,i.e.,the type of biostimulant, were as follows: (1)the foliar application of Seaweed Extract at concentrations of 500,1000,and 2000 ppm; (2)HA at concentrations of 150,300,and 600 ppm; (3)the inoculation of the bed with Myco-Root biofertilizer with a concentration ranging from 107 to 108 CFU/gr; (4)a control treatment without the use of biostimulators.
2.3Data Collection
2.3.1Morphological Traits
At the end of the experiment,various morphological and growth parameters were measured to evaluate the effects of biostimulators on tuberose plants under water-deficit conditions. The measured parameters included the number of leaves and flowering stems per plant, the leaf area, the diameter of the flowering stem, the length of the flowering spike, the number of flower buds in the spike, and the diameter of the spike. Additionally, the fresh and dry weights of the flowering stems and spikes were also measured to assess the overall biomass production of the plants.
2.3.2.Physiological Indices
Photosynthetic Pigments
We took 0.5 g of fresh plant leaf sample,accurately weighted, and homogenized it in a mortar with liquid nitrogen. Then, 20 mL of 80% acetone solvent was added to the homogenized sample mixture. The mixture was centrifuged at 6000 rpm for 10 min. The supernatant was separated and analyzed for chlorophyll a,chlorophyll b, and carotenoids content using a spectrophotometer. The spectral absorbance of chlorophyll a, chlorophyll b, and carotenoids was calculated using the following equation(Equation(1)).
Chlorophyll a = 15.65 A666 – 7.340 A653
Chlorophyll b = 27.05 A653 – 11.21 A666
Total Chlorophyll = Chl.a+Chl.b
Carotenoids = 1000(A470) – 2.27(mg chl.a) – 81.4(mg chl.b)/227 (1)
Phenolic Compounds
We estimated the total phenol contents using the Folin–Ciocalteu reagent method, and solid-phase extraction(SPE) was used to remove non-phenolic combinations. A diluted extract of the sample(0.5 mL of 1:10 g/mL) or gallic acid, used as a standard, was mixed with Folin–Ciocalteu reagent(5 mL, 1:10 diluted with distilled water) and aqueous Na2CO3(4 mL, 1 M). The mixture was allowed to stand for 10 min, and the absorbance was measured via colorimetry at 765 nm. A standard curve was prepared using 0,50,100,150,200,and 250 mg/l solutions of gallic acid in a methanol–water(50:50,v/v) solution. Total phenol contents were expressed in terms of gallic acid equivalents(mg/g of dry mass), with gallic acid used as the reference compound.
Total Carbohydrates
The phenol-sulphuric acid method was used to determine the carbohydrates content of the samples. Then, 0.1 g of powder of each accession was mixed with 5 mL of 2.5 N-HCl and heated in a water bath for 3 h. The mixture was then neutralized by adding sodium carbonate and the volume was increased to 100 mL. Glucose was used as the standard for carbohydrate estimation. Each experimental sample(standard and maize accessions) was mixed with 1 mL of 5% phenol solution and 5 mL of 96% sulphuric acid solution and incubated at 30℃ for 20 min. After incubation, the absorbance was measured at 490 nm and a linear regression equation(Equation(2)) was used to estimate the carbohydrate content of the selected maize accessions.
Proline Estimation
Proline content in the explant tissues was extracted and analyzed according to the method of. Samples(100 mg) were homogenized in aqueous sulfosalicylic acid(3%w/v; 10 mL) and stored at room temperature for 48 h. The mixture was then centrifuged at 10,000 rpm for 10 min. Subsequently, 2 mL of supernatant was reacted with an equal volume of each ninhydrin reagent(5 g ninhydrin in 120 mL of glacial acetic acid and 48 mL distilled water,and 32 mL H3PO4) and glacial acetic acid. The reaction mixture was then placed in a bain-marie at 70℃ for 1 h and cooled in an ice bath. The reaction mixture was vigorously mixed with 5 mL toluene using a stirrer for 10–15 s, allowing the tubes to stand at least for 20 min in darkness at room temperature for toluene-and aqueous-phase separation. The toluene phase was carefully poured into test tubes, and the absorbance was measured at 520 nm using a spectrophotometer. The concentration of proline was calculated from a standard curve using the following equation: (µg proline in extract/115.5)/g sample=µmol/g FW.
Results
Variance analysis revealed that the morphological and physiological indices of tuberose were influenced in different ways by the factors of different water conditions and biostimulants in the present study. Mean comparisons were presented for indices that were significant under the interaction of both water deficits and biostimulant factors. The results showed that biostimulator treatments had different significant effects on alleviating the negative effects of water deficits on tuberose characteristics.
3.1.Morphological Traits
The results of the variance analysis(Table2)indicated that tuberose growth characteristics were significantly (p<0.05) affected by water-deficit treatments and biostimulant treatments,as well as their interaction. Specifically, the results showed that water-deficit treatments significantly impacted leaf number, the leaf fresh and dry weight, and the root fresh and dry weight. Biostimulant treatments also significantly affected all growth characteristics, except for root dry weight. Furthermore, the interaction between the water deficit and biostimulators had a significant impact on leaf fresh and dry weight and on root fresh weight.
| df | Leaf Number | Leaf Fresh Weight | Leaf Dry Weight | Root Fresh Weight | Root Dry Weight |
| 7 | 12.399 ** | 573.417 ** | 58.643 ** | 3.169 ** | 0.258 ** |
| 3 | 58.558 ** | 48.188 ** | 3.881 ** | 2.230 ** | 0.097 ns |
| 21 | 3.470 ns | 16.188 ** | 2.896 ** | 0.915 ** | 0.093 ns |
| 64 | 2.76 | 1.184 | 0.143 | 0.34 | 0.06 |
** = significant at p < 0.01; ns = not significant at p = 0.05
Both bulb fresh and dry weight, as well as bulb leaf number, were significantly (p<0.05) influenced by the factors of water-deficit and biostimulant treatments(Table3). However, neither water-deficit nor biostimulant treatments had a significant effect on bulb leaf fresh weight.The results also showed the significant effect of the interaction between the two factors on bulb fresh and dry weight, bulb leaf number, and bulb leaf fresh weight(Table3). Moreover, the results revealed that biostimulators and their interaction with water deficit had no significant effects on bulb leaf dry weight, whereas water deficit treatments significantly impacted this characteristic of bulb leaves.
| df | Bulb Fresh Weight | Bulb Dry Weight | Bulb Leaf Fresh Weight | Bulb Leaf Dry Weight | Bulb Leaf Number |
| 7 | 167.276 ** | 7.578 ** | 0.223 ns | 0.122 ** | 10.527 ** |
| 3 | 63.527 ** | 3.278 ** | 0.442 ns | 0.007 ns | 4.333 ** |
| 21 | 16.323 ** | 0.891 ** | 0.766 ** | 0.026 ns | 1.4 ** |
| 64 | 6.741 | 0.49 | 0.296 | 0.017 | 0.468 |
** = significant at p < 0.01; ns = not significant at p = 0.05.
The mean comparisons showed that biostimulator treatments could enhance the morphological indices of tuberose under water-deficit conditions(Table4). The highest amounts of leaf fresh and dry weight, root fresh weight,bulb fresh and dry weight, bulb leaf number, and bulb leaf fresh weight were obtained under 100%FC irrigation with the application of mycorrhiza and 2000 ppm of Seaweed Extract treatments. Moreover,under other water conditions, there were significant differences between the effects of treatments. For example, in the 80%FC irrigation, the application of 150 and 300 ppm of HA, respectively, resulted in higher fresh and dry weights of leaves. However, the mean comparisons for underground characteristics showed no significant difference between the effects of some biostimulant treatments on root fresh weight, bulb fresh and dry weight, bulb leaf number, and bulb leaf fresh weight compared to the control conditions under 100% and 80%FC irrigation(Table4). In contrast,under 60%and 40%FC irrigation,the treatment with Seaweed Extract(2000 ppm) had a greater effect on increasing leaf fresh and dry weight compared to other biostimulator treatments. Additionally, under these irrigation regimes, the application of biostimulant treatments could increase the fresh and dry weights of underground characteristics compared to the control treatment.
| Water Deficit | Biostimulant Treatments | Leaf Fresh Weight (g) | Leaf Dry Weight (g) | Root Fresh Weight (g) | Bulb Fresh Weight (g) | Bulb Dry Weight (g) | Bulb Let Number | Bulblet Fresh Weight (g) |
| SE 500 ppm | 81.83 | 9.12 | 3.50 | 19.38 | 3.83 | 5.00 | 3.86 | |
| SE 1000 ppm | 80.55 | 8.54 | 3.48 | 22.03 | 3.77 | 5.66 | 3.87 | |
| SE 2000 ppm | 85.24 | 11.03 | 5.60 | 29.23 | 5.00 | 6.33 | 4.63 | |
| 100% FC | HA 150 ppm | 75.89 | 7.26 | 4.52 | 21.06 | 4.32 | 5.00 | 4.21 |
| HA 300 ppm | 78.36 | 8.07 | 3.66 | 18.18 | 3.93 | 5.33 | 3.40 | |
| HA 600 ppm | 77.38 | 7.35 | 4.00 | 16.30 | 3.28 | 4.00 | 3.80 | |
| M | 88.81 | 11.79 | 3.65 | 14.35 | 2.63 | 3.00 | 6.17 | |
| C | 74.06 | 6.43 | 5.15 | 23.04 | 4.49 | 5.66 | 4.06 | |
| SE 500 ppm | 72.16 | 6.08 | 3.33 | 16.16 | 3.14 | 4.00 | 4.04 | |
| SE 1000 ppm | 72.20 | 5.37 | 4.26 | 18.34 | 3.61 | 4.33 | 3.95 | |
| SE 2000 ppm | 72.43 | 5.57 | 4.60 | 20.28 | 3.97 | 4.66 | 4.34 | |
| 80% FC | HA 150 ppm | 73.92 | 6.82 | 4.05 | 15.71 | 2.85 | 4.00 | 4.00 |
| HA 300 ppm | 72.96 | 7.09 | 3.58 | 14.49 | 3.09 | 3.33 | 4.40 | |
| HA 600 ppm | 71.09 | 5.08 | 3.14 | 15.76 | 3.22 | 3.66 | 4.35 | |
| M | 77.01 | 6.77 | 3.66 | 14.53 | 3.05 | 3.33 | 4.39 | |
| C | 72.01 | 5.99 | 5.22 | 21.01 | 4.20 | 5.33 | 3.94 | |
| SE 500 ppm | 70.99 | 5.12 | 3.24 | 15.79 | 3.00 | 3.66 | 4.35 | |
| SE 1000 ppm | 72.15 | 5.85 | 4.26 | 14.85 | 3.14 | 3.33 | 4.50 | |
| SE 2000 ppm | 72.44 | 8.87 | 3.35 | 14.82 | 3.05 | 3.66 | 4.08 | |
| 60% FC | HA 150 ppm | 69.27 | 5.06 | 3.45 | 14.97 | 3.08 | 3.66 | 4.11 |
| HA 300 ppm | 70.42 | 5.50 | 2.88 | 13.14 | 2.17 | 3.00 | 4.37 | |
| HA 600 ppm | 70.55 | 5.88 | 3.77 | 14.60 | 2.86 | 3.66 | 4.03 | |
| M | 71.20 | 6.05 | 3.29 | 13.97 | 2.23 | 3.33 | 3.95 | |
| C | 69.85 | 5.94 | 3.32 | 14.95 | 2.85 | 3.33 | 4.49 | |
| SE 500 ppm | 70.44 | 5.06 | 3.83 | 14.79 | 2.37 | 4.00 | 3.73 | |
| SE 1000 ppm | 70.42 | 5.08 | 4.14 | 20.04 | 4.23 | 5.66 | 3.52 | |
| SE 2000 ppm | 72.16 | 5.52 | 3.60 | 15.12 | 2.73 | 3.66 | 4.09 | |
| 40% FC | HA 150 ppm | 68.82 | 5.08 | 4.14 | 18.35 | 3.74 | 4.66 | 3.92 |
| HA 300 ppm | 69.29 | 5.03 | 3.15 | 13.97 | 2.23 | 4.33 | 4.21 | |
| HA 600 ppm | 66.53 | 5.00 | 2.38 | 11.07 | 1.15 | 2.00 | 4.36 | |
| M | 68.79 | 5.43 | 2.90 | 11.56 | 1.63 | 3.00 | 3.90 | |
| C | 66.94 | 5.36 | 3.71 | 15.93 | 3.19 | 4.00 | 2.24 |
FC; field capacity, SE; seaweed extract, HA; humic acid, M; mycorrhiza, C; control.
Means within columns followed by different letters are significantly different by means comparisons at p ≤ 0.05.
The results of flower characteristics showed that both water-deficit and biostimulator treatments, as well as their interaction, had a significant impact on the flower characteristics of tuberose,including flower stem length, spike diameter, flower stem fresh weight,and dry weight(Table5).
| df | Flower Stem Length | Flower Diameter | Spike Fresh Weight | Spike Dry Weight |
| 7 | 1827.14 ** | 232.09 ** | 103.34 ** | 1.40 ** |
| 3 | 109.42 ** | 15.42 ** | 19.65 ** | 0.53 ** |
| 21 | 8.42 ** | 0.72 ** | 0.50 ** | 0.01 ** |
| 64 | 1.51 | 0.40 | 0.17 | 0.005 |
** = significant at p < 0.01.
The indices of flower stem and spikes were significantly influenced by water deficits and biostimulants. The application of biostimulant treatments significantly alleviated the negative effects of water deficits on the flowering indices of tuberose. The mean comparisons showed that the highest flower stem length was obtained with the application of 2000 ppm of Seaweed Extract under 100%and 80%FC irrigation conditions(Table6), while the lowest length of flower stem was observed under irrigation of 40%FC and control conditions, although there was no significant difference between control with HA and mycorrhiza treatments for flower stem length. Moreover, all biostimulant treatments significantly increased flower diameter under the irrigation regimes compared to the control treatment. The highest diameter of flowers was achieved under 100%FC irrigation with mycorrhiza symbiosis and the application of 600 ppm of HA(Table6). Additionally, in 60%and 80%FC irrigation, the highest fresh and dry weight of spike was obtained with the application of 2000 ppm of Seaweed Extract. The lowest amounts of spike fresh and dry weight were achieved under 40%FC irrigation in control conditions. Furthermore, under water-deficit conditions in 60% and 40%FC irrigation, the biostimulant treatments enhanced the flowering characteristics of tuberose compared to the control condition, with the treatment of 2000 ppm of Seaweed Extract having more significant effects on reducing the effects of water deficits.
| Water Deficit | Biostimulant Treatments | Flower Stem Length (cm) | Flower Diameter (mm) | Spike Fresh Weight (g) | Spike Dry Weight (g) |
| SE 500 ppm | 61.68 | 11.55 | 12.20 | 1.46 | |
| SE 1000 ppm | 64.96 | 17.08 | 12.28 | 1.77 | |
| SE 2000 ppm | 68.84 | 17.28 | 13.17 | 1.98 | |
| 100% FC | HA 150 ppm | 62.31 | 16.01 | 10.62 | 1.23 |
| HA 300 ppm | 63.60 | 16.78 | 11.25 | 1.42 | |
| HA 600 ppm | 63.70 | 18.02 | 11.74 | 1.64 | |
| M | 64.50 | 17.99 | 11.36 | 1.42 | |
| C | 57.98 | 13.82 | 7.93 | 1.13 | |
| SE 500 ppm | 62.41 | 16.84 | 11.04 | 1.34 | |
| SE 1000 ppm | 67.10 | 17.10 | 11.94 | 1.70 | |
| SE 2000 ppm | 69.45 | 17.01 | 12.68 | 1.86 | |
| 80% FC | HA 150 ppm | 59.94 | 15.61 | 10.06 | 1.23 |
| HA 300 ppm | 60.00 | 17.05 | 10.71 | 1.45 | |
| HA 600 ppm | 57.95 | 17.37 | 11.05 | 1.60 | |
| M | 57.78 | 17.23 | 10.19 | 1.39 | |
| C | 56.07 | 13.37 | 7.28 | 1.13 | |
| SE 500 ppm | 50.81 | 12.34 | 8.99 | 1.31 | |
| SE 1000 ppm | 53.90 | 12.59 | 9.64 | 1.33 | |
| SE 2000 ppm | 55.08 | 13.50 | 9.58 | 1.46 | |
| 60% FC | HA 150 ppm | 50.47 | 12.68 | 8.12 | 1.15 |
| HA 300 ppm | 51.15 | 13.32 | 8.72 | 1.19 | |
| HA 600 ppm | 51.17 | 13.34 | 8.80 | 1.37 | |
| M | 49.99 | 13.82 | 8.08 | 1.22 | |
| C | 45.96 | 11.21 | 6.22 | 0.88 | |
| SE 500 ppm | 43.09 | 9.20 | 10.62 | 1.04 | |
| SE 1000 ppm | 46.35 | 10.30 | 7.66 | 1.10 | |
| SE 2000 ppm | 49.33 | 11.26 | 7.93 | 1.23 | |
| 40% FC | HA 150 ppm | 43.07 | 9.33 | 6.04 | 0.86 |
| HA 300 ppm | 44.95 | 9.71 | 6.71 | 0.94 | |
| HA 600 ppm | 46.43 | 11.31 | 6.89 | 1.01 | |
| M | 44.13 | 11.51 | 6.84 | 0.96 | |
| C | 41.92 | 8.31 | 5.03 | 0.68 |
FC; field capacity, SE; seaweed extract, HA; humic acid, M; mycorrhiza, C; control.
Means within columns followed by different letters are significantly different by means comparisons at p ≤ 0.05.
3.2.Physiological Indices
3.2.1.Photosynthesis Pigments
The results of the variance analysis showed that the photosynthesis pigments of tuberose were significantly (p<0.05) affected by the separate effects of both water-deficit and biostimulator factors(Table7). However, the interaction between water deficits and biostimulators had no significant effect on the assessed photosynthesis pigments, including chlorophyll a, b, and total chlorophyll, as well as carotenoids.
| df | Chl a | Chl b | Total Chl | Carotenoid |
| 7 | 0.721 * | 1.707 ** | 4.574 ** | 0.307 ns |
| 3 | 2.730 ** | 0.82 ** | 4.223 ** | 9.884 ** |
| 21 | 0.192 ns | 0.225 ns | 0.344 ns | 0.302 ns |
| 64 | 0.205 | 0.193 | 0.365 | 0.313 |
** = significant at p < 0.01; * = significant at p < 0.05; ns = not significant at p = 0.05; df = degree of freedom; Chl = chlorophyll.
3.2.2.Carbohydrates and Secondary Metabolites
The results showed that the metabolites of tuberose were significantly affected by biostimulator treatments and their interaction with water deficits. However, the separate effects of water deficits were significant on carbohydrates and proline, but had no significant effects on phenolic compounds and flavonoids(Table8).
| df | Phenolic Compounds | Flavonoids | Carbohydrates | Proline |
| 7 | 0.055 ns | 0.007 ns | 0.233 ** | 0.048 ** |
| 3 | 0.209 ** | 0.061 ** | 0.145 ** | 0.000 ** |
| 21 | 0.068 ** | 0.015 ** | 0.022 ** | 0.000 ** |
| 64 | 0.045 | 0.008 | 0.000 | 0.000 |
** = significant at p < 0.01; ns = not significant at p = 0.05
| Water Deficit | Biostimulant Treatments | Phenolic Compounds | Flavonoids | Carbohydrates | Carbohydrates |
| SE 500 ppm | 0.416 | 0.047 | 0.20 | 0.503 | |
| SE 1000 ppm | 0.525 | 0.084 | 0.19 | 0.504 | |
| SE 2000 ppm | 0.439 | 0.034 | 0.19 | 0.510 | |
| 100% FC | HA 150 ppm | 0.130 | 0.16 | 0.31 | 0.514 |
| HA 300 ppm | 0.359 | 0.21 | 0.37 | 0.512 | |
| HA 600 ppm | 0.473 | 0.15 | 0.39 | 0.511 | |
| M | 0.489 | 0.20 | 0.40 | 0.506 | |
| C | 0.689 | 0.24 | 0.33 | 0.523 | |
| SE 500 ppm | 0.847 | 0.092 | 0.22 | 0.528 | |
| SE 1000 ppm | 0.710 | 0.11 | 0.21 | 0.535 | |
| SE 2000 ppm | 0.495 | 0.095 | 0.21 | 0.546 | |
| 80% FC | HA 150 ppm | 0.211 | 0.082 | 0.33 | 0.535 |
| HA 300 ppm | 0.454 | 0.10 | 0.34 | 0.53 | |
| HA 600 ppm | 0.643 | 0.15 | 0.38 | 0.534 | |
| M | 0.629 | 0.27 | 0.44 | 0.525 | |
| C | 0.684 | 0.34 | 0.43 | 0.555 | |
| SE 500 ppm | 0.593 | 0.064 | 0.31 | 0.573 | |
| SE 1000 ppm | 0.843 | 0.082 | 0.28 | 0.580 | |
| SE 2000 ppm | 0.768 | 0.095 | 0.27 | 0.568 | |
| 60% FC | HA 150 ppm | 0.451 | 0.25 | 0.39 | 0.578 |
| HA 300 ppm | 0.465 | 0.26 | 0.40 | 0.570 | |
| HA 600 ppm | 0.665 | 0.23 | 0.45 | 0.567 | |
| M | 0.756 | 0.24 | 0.68 | 0.564 | |
| C | 0.678 | 0.22 | 0.50 | 0.587 | |
| SE 500 ppm | 0.614 | 0.10 | 0.70 | 0.612 | |
| SE 1000 ppm | 0.916 | 0.06 | 0.41 | 0.611 | |
| SE 2000 ppm | 0.834 | 0.10 | 0.30 | 0.611 | |
| 40% FC | HA 150 ppm | 0.567 | 0.33 | 0.39 | 0.617 |
| HA 300 ppm | 0.761 | 0.36 | 0.41 | 0.616 | |
| HA 600 ppm | 0.776 | 0.18 | 0.43 | 0.613 | |
| M | 0.721 | 0.16 | 0.84 | 0.605 | |
| C | 0.469 | 0.10 | 0.62 | 0.622 |
FC; field capacity, SE; seaweed extract, HA; humic acid, M; mycorrhiza, C; control.
Means within columns followed by different letters are significantly different by means comparisons at p ≤ 0.05.
The results showed that there was a significant difference among the effects of water-deficit levels on the concentrations of phenol, flavonoid, carbohydrate, and proline in leaves of tuberose. Moreover, the application of biostimulants can alleviate the negative effects of water deficits on the secondary metabolites of tuberose. Consequently, biostimulant treatments led to an increase in the concentrations of phenolic compounds, flavonoids, carbohydrates, and proline content in the leaves of tuberose. The treatments of 1000 and 2000 ppm of Seaweed Extract and 300 and 600 ppm of HA had a more positive effect on increasing the total phenolic compounds under water deficits under 60%and 40%FC, while the lowest amounts of total phenolic compounds were obtained in control treatments under irrigation conditions of 40%FC(Table9).
A higher flavonoid concentration was obtained under 40%FC irrigation and with the treatments of 150 and 300 ppm of HA, and a lower amount of flavonoid was observed in control conditions under 40%FC with a water deficit. However, there were no significant differences between control treatments with mycorrhiza, 600 ppm HA, and 500 and 2000 ppm Seaweed Extract(Table9). The highest concentration of total carbohydrates was obtained through mycorrhiza symbiosis with the tuberose plant under a 40%FC water deficit, and the lowest concentration of carbohydrates was obtained in control conditions under irrigation with 40%FC(Table9). However, there was no significant effect among biostimulant treatments and the control condition under 40%FC irrigation on proline concentration, except mycorrhiza. Tuberose plants grown with mycorrhizal symbiosis had lower concentration of proline than plants grown in control treatments under 40%FC irrigation(Table9).
Discussion
Drought stress poses a significant challenge to agricultural plant production, adversely impacting the growth and development of various plant species. The results of the current study showed that the morphological and physiological indices of tuberose were significantly affected by water deficit. The morphological indices were significantly reduced under various levels of water stress. In the present study,the decreasing number of leaves, leaf area, and stem length are possibly attributable to an increasing water deficit, leading to limited cellular water for cell division and cell elongation. These findings are consistent with previous studies, which reported that a water-deficit stress limits stem growth and the development of cut flowers. Similarly, another study found that the drought stress led to a reduction in the leaf area, stem length, and fresh weight of Zinnia elegans. The effects of water deficit on the morphological indices of cut flower stems can have significant implications for their marketability, as reduced quality traits can result in lower profits in floriculture trading. However, the application of biostimulants in the current study showed that these compounds can have positive effects, enhancing growth parameters and mitigating the negative impacts of water deficit on tuberose. The positive effects of biofertilizers contribute to the improvement of root growth, consequently improving water absorption under stress conditions, and play role in the production and accumulation of acclimatizing osmolytes in plants.
In this respect, Zulfiqar et al. reported that biostimulants can serve as an effective tool in mitigating the adverse effects of abiotic stresses, including drought, salinity, heavy metals, and extreme temperatures, which limit plant production. These compounds act by altering gene expression, metabolism, and phytohormone production, as well as by encouraging the accumulation of compatible solutes and antioxidants, ultimately leading to enhanced plant growth under stress conditions. The findings of the current study demonstrate that the use of Seaweed Extract can significantly mitigate the adverse impacts of water deficit on the development of tuberose. Previous studies have shown the significant effects of Seaweed Extract on alleviating the negative effects of drought stress on pot marigold(Calendula officinalis L.), chicory(Cichorium intybus L.), and sugarcane(Saccharum hybrids). Mycorrhiza and acid humic are others biostimulants that play significant roles in alleviating the adverse effects of water deficits on the growth of tuberose. Mycorrhiza, with its strategic associations between plant roots and soil-borne symbiotic fungi, plays a pivotal role in enhancing the drought tolerance of existing plants. Another study showed that incubating the African marigold(Tagetes erecta) plant with mycorrhizal fungus stimulated all growth indices compared to non-treated plants.
A water deficit is known to cause significant physiological changes in plants, including alterations in photosynthetic activity and efficiency. The results of this study demonstrate that water deficits and biostimulators independently affect pigment content, but their interaction has no significant impact on chlorophyll a, b, total chlorophyll, or carotenoids(Table7). Under different levels of water stress, tuberose exhibited increased relative water content(RWC) and chlorophyll levels, indicating better physiological performance despite stress. Aubert et al. reported an increase in chlorophyll content in two buckwheat species, Fagopyrum esculentum and Fagopyrum tataricum, under moisture stress. This increase in chlorophyll is a resilience strategy used to preserve the efficiency of the light phase of photosynthesis. It should also be pointed out that the effect of water stress on chlorophyll content varies according to species and variety. Nonetheless, depending on the cultivar,water stress considerably reduces total chlorophyll content whilst increasing carotenoid content in the leaves of tuberose plants. This reduction in total chlorophyll content can be linked to chlorophyll degradation or pigment photooxidation. Moreover, this decrease in chlorophyll is accompanied by a reduction in stomatal conductance(drought leads to stomatal closure, thus limiting the entry of carbon dioxide required for photosynthesis) and the production of antioxidant enzymes such as superoxide dismutase, catalase, and peroxide dismutase in tuberose plants. The lack of significant interaction effects in this study indicates that the biostimulators may not effectively modify pigment responses under the tested conditions.
The results also indicated the significant impact of water-deficit levels on the concentrations of various secondary metabolites in tuberose leaves, particularly carbohydrates and proline. Studies by Shakarami et al. and Ali et al. illustrated that, depending on the tuberose plant cultivar, proline content increased in tuberose plants under water stress conditions. The accumulation of proline and carbohydrates is one of the adaptive strategies frequently observed in a large number of species in response to various environmental constraints. It has been observed that proline can function as a chaperone molecule capable of protecting protein integrity and enhancing the activity of certain enzymes. Thus, the accumulation of proline during water stress creates a sphere of hydration around the pro-tein, preventing it from becoming depleted. Increased proline content has an inhibitory effect on the chlorophyll precursor glutamate, reducing its involvement in chlorophyll synthesis. During the water deficits, stomatal closure reduces CO2 availability, leading to a reduction in Calvin cycle activity and, consequently, a decrease in the consumption of the reducing power NAD(P)H/H+. Activating proline biosynthesis in chloroplasts would attenuate this phenomenon. An increase in carbohydrate content in tuberose plants may be associated with either impaired storage or increased accumulation of soluble sugars,indicating a potential adaptive response to high stress. Indeed,the levels of carbohydrates such as sucrose,glucose,and fructose may increase as plants convert other carbohydrates in order to maintain osmotic pressure, facilitating water uptake and reducing the rate of transpiration. Furthermore,carbohydrate accumulation correlates with increased antioxidant enzyme activity,mitigating oxidative damage during drought in tuberose plants.
This study highlights that,under severe water stress(40%FC), the lowest levels of total phenolic compounds were observed in the control treatment. The application of biostimulants, such as Seaweed Extract and HA, proved effective in mitigating the negative effects of moisture stress. Additionally, flavonoid concentrations in tuberose plants were significantly higher under 40%FC irrigation when treated with 150 and 300 ppm of HA. Studies by Khorasaninejad et al. showed that HA application reduced total phenol content while increasing flavonoid content in the aerial parts of purple Echinacea(Echinacea purpurea L.) under water-deficit stress. Phenolic compounds act as antioxidants,neutralizing reactive oxygen species(ROS) and protecting plant cells from oxidative damage. This is particularly true for flavonoids, which are members of the polyphenol family; their biosynthesis gene expression is significantly higher when exposed to stress. Flavonoids participate in defense mechanisms by scavenging free radicals and buffering membranes from lipid peroxidation. HA improves photosynthetic parameters by increasing Rubisco enzyme activity, gas exchange, electron transport, photosynthetic rate, and stomatal conductance in plants under drought stress. Seaweed Extracts are also known to enhance plant resilience to water stress by boosting antioxidant defense mechanisms. Since seaweed is rich in natural antioxidants and various minerals, including Fe ,Mg, K, and Ca, it can improve physiological characteristics such as water retention, nutrient uptake(notably nitrogen), and overall plant vigor. The foliar application of Seaweed Extracts and chitosan increases total nitrogen, phosphorus, potassium, chlorophyll, and carotenoid content in tuberose leaves. Investigations performed by Sewedan et al. exhibited that the foliar application of 15%Spirulina platensis extract improved chlorophyll content in tuberose plant leaves. Seaweed Extracts reduced phenol content and increased indole acetic acid(IAA) content in the leaves of wheat plants under conditions of water stress and reduced nitrogen fertilization. This may be ascribed to the fact that Seaweed Extracts are rich in magnesium, auxins, cytokinins, amino acids, gibberellins, and vitamins, which can enhance growth characteristics by promoting cell division and differentiation and enzymatic activity, maintaining chloroplast osmotic potential and improving photosynthetic capacity.
This study also revealed that mycorrhizal symbiosis significantly increased the total carbohydrate concentration in tuberose seedlings under a 40%FC water deficit. These results are consistent with those of Bitaraf et al., in which wheat seedlings mycorrhized by G.mosseae exhibited a carbohydrate content of 15.80%, compared to the control under water-stressed conditions. AMF regulate carbon metabolism by altering sucrose biosynthesis and invertase gene expression, which are vital for plant development under water stress. Mycorrhizal colonization enhances photosynthetic capacity, which is essential for carbohydrate production during periods of water shortage. AMF improve drought resilience through mechanisms such as enhanced water and nutrient uptake, antioxidant defenses, and hormonal modulation, all of which collectively support carbohydrate synthesis.
Tuberose plants associated with AMF exhibited lower proline levels than the control group, suggesting a more efficient stress response mechanism. These findings align with those of. This reduction in proline could be linked to the ability of AMF to enhance the nutrition of tuberose plants, promoting better tolerance to water stress. Research by Al-Arjani et al.demonstrated that the application of AMF species such as G.etunicatum, Gl.intraradices, and G.mosseae improved proline content in the stems of Ephedra foliata Boiss. under water stress conditions. This reduction was accompanied by the upregulation of biosynthetic enzymes involved in proline synthesis, as well as improved magnesium uptake(essential for chlorophyll formation) and nitrogen uptake(through the activation of key enzymes involved in nitrogen assimilation, such as nitrate reductase and glutamate synthetase). AMF can stabilize the photosynthetic apparatus, enhancing electron transport and helping to maintain higher relative water content in plant tissues, which reduces oxidative stress markers such as malondialdehyde(MDA)during drought. Recent studies have shown that plant symbiosis with arbuscular fungi induces the expression of specific phosphorus and nitrogen transporters.
Conclusions
This study demonstrates a better understanding of the responses of tuberose plants to water deficits. These can be exploited for the optimization of growth and maximization of cut flower yield. The findings revealed that the application of biostimulants contributes to the mitigation of negative effects of water deficit in tuberose production under greenhouse condition as an irrigation water conservation strategy while maintaining yields. This study also highlights the effectiveness of biostimulants in sustaining tuberose growth and flowering responses across different water-deficit irrigation strategies. The use of Seaweed Extract under water-deficit conditions at 60% field capacity is efficient for the conservation of water resources and minimization of any adverse effects of water deficits on species growth and productivity. Results of this research are invaluable for advising flower producers on how to minimize agricultural water consumption.
Different crops will have different suitable seaweed extract irrigation strategies. Dora seaweed extracts include Ecklonia maxima, Ascophyllum nodosum, Sargassum, and three-in-one algae to choose from.
