Salinity is a major impediment to crop production. This study was undertaken to compare the effect of seaweed extract, humic acid, and potassium sulfate nanoparticles in alleviating salt stress in Alfalfa ( Medicago sativa L.). Seeds of ten alfalfa genotypes were germinated in a growth chamber at five salt concentrations (0%, 0.5%, 1.0%, 1.5%, and 2.00%). Salt concentrations above 1% reduced seed germination by more than 70% in most genotypes. One salt tolerant genotype (Mesa-Sirsa) and one salt sensitive (Bulldog 505) were selected and planted in greenhouse pots containing 2 kg of sand and subjected to two salt levels (10 and 15 dS· m -1). Four treatments consisting of 1) control (Hoagland solution, no-salt), 2) seaweed extract at 4 Kg·ha -1, 3) humic acid at 28 L· ha -1, and 4) potassium sulfate at 300 Kg· ha -1. Plant biomass was reduced under both salt concentrations in both genotypes, with a greater magnitude in the salt sensitive genotype. Application of seaweed extract resulted in higher relative water content and proline under both salt concentrations (10 and 15 dS·m -1) in the salt sensitive genotype, and lower electrolyte leakage in both salt tolerant and salt sensitive genotypes, under both salt concentrations. Seaweed extract also resulted in higher catalase and SOD activities in both genotypes under 10 dS·m -1. Catalase and SOD activities were associated with significantly (p < 0.01) reduced electrolyte leakage and increased shoot dry weight. Overall, seaweed extract seemed to have a positive effect in alleviating salt stress in alfalfa.
About 900,000 ha of Egypt’s agricultural lands are suffering from salinity build- up problem [
Several studies carried out to elucidate salinity tolerance mechanisms included the application of biological stimulants and organic acids [
Humic substances have shown anti-stress effects under abiotic stress conditions such as unfavorable temperature, salinity, and low pH [
Plants require K for a number of important physiological processes including the activation of various enzymes, the synthesis and metabolism of carbohydrates, protein synthesis, and the opening and closing of stomata thus controlling gas exchange and photosynthesis [
Alfalfa (Medicago sativa L.), is an important forage crop grown over 32 million hectares globally [
The primary objective of this study was to explore the effect of different growth-enhancing substances, such as seaweed extract, humic acid, and potassium sulfate, on alfalfa growth and physiological response under salt stress.
Alfalfa seeds were germinated in 100-mm petri plates containing a single piece of Whatman No. 2 filter paper imbibed with two types of saline solutions. The first solution consisted of NaCl and the second was a mixture of (NaCl, MgCl2・6H2O and Na2SO4), the most common active ingredients in seawater. Each saline solution was added in five concentrations 0%, 0.5%, 1%, 1.5% and 2% (wt/wt) in deionized water. Twenty-five scarified seeds from each of ten alfalfa genotypes that were described as salt tolerant (Malone, Mesa-Sirsa, Rambler, and Saranac) and salt sensitive (Barricade, Bulldog 505, Hybriforce 2600, Magna 801FQ, 3010, and CW1010) were placed in each petri plate. Four and a half (4.5) mL of each salt solution with the appropriate concentration was added to each plate. The experimental design was a split-plot in a randomized complete block design with three treatments. Salt solutions represented the main plots and the increasing concentrations represented the sub-plots. The germination test was conducted in a dark growth chamber at 25˚C for 14 days. Seed germination percentage (GP) was calculated as:
where G = number of germinated seeds, and TS = total number of seeds.
One alfalfa salt-tolerant genotype (Mesa-Sirsa) and one salt-sensitive (Bulldog 505) were selected based on the results of the seed germination experiment described above. Six seeds from each genotype were planted in pots containing 2 kg sand and lined with plastic bags. Seedlings within each pot were thinned after four weeks from planting to keep four plants per pot. The plants were gradually subjected to two levels of salt concentrations starting at five weeks after planting. Calcium chloride (CaCl2・2H2O) and sodium chloride (NaCl) were mixed in a 2:1 proportion (CaCl2:NaCl) and added to Hoagland solution to make two saline nutrient solutions of 10 and 15 dS・m−1 electrical conductivity. The moisture level in the pots was kept at field capacity. Four treatments consisting of 1) control (Hoagland solution), 2) seaweed extract from Ascophyllum nodosum (Organic Approach, Lancaster, PA) at 4 Kg・ha−1, (3) humic acid (KELP4LESS, Idaho Falls, ID) at 28 L・ha−1, and 4) potassium sulfate nanoparticles at 300 kg・ha−1. Humic acid and seaweed extract were applied once at one week after the start of salt treatments, whereas potassium sulfate was added in 2 split applications, the first application was one week following salt application and the second at bud stage. All treatments were irrigated with Hoagland solution when needed. Plants were harvested 90 days after planting. Soil characteristics and chemical composition were recorded at the beginning of the study (
Relative water content (RWC) of shoots was measured according to Turner [
where, FW = fresh weight, TW = turgor weight, and DW = dry weight. Dry weight was estimated by drying the samples in a convection oven at 80˚C for 48 h. Turgor weight was determined by floating the shoots on water at room
Sand | 100.0% | Mineral concentration (mg・kg−1) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Silt | 0.0% | Ca | Mg | Na | K | Cl | NH4-N | NO3-N | P | Fe |
Clay | 0.0% | 35.17 | 5.94 | <1.79 | 2.55 | 8.70 | <6.40 | <0.17 | 0.97 | 5.46 |
Soil Type | Sand | |||||||||
EC1 | 0.011 dS・m−1 | Zn | B | Mn | Cu | Mo | Cd | Cr | Ni | Pb |
pH | 6.68 | 0.33 | 0.775 | 0.88 | 0.29 | <0.04 | <0.04 | 0.04 | <0.04 | 0.36 |
CEC2 | 0.21 meq. 100 g-1 | |||||||||
OM3 | 0.01% |
1EC: Electrical conductivity in dS・m−1. 2CEC: Cation exchange capacity in meq.100 g−1 soil. 3OM: Organic matter.
temperature for 48 h. Relative yield was determined according to Isla & Aragüés [
Free proline content in plant tissue was determined according to the methods of Bates et al. [
Electrolyte leakage (EL) was determined as described by Lutts et al. [
Tissue samples of 0.2 g from each leaf were homogenized with 50 mM sodium phosphate buffer (pH 7.0) containing 1 mM ethylenediaminetetraacetic acid (EDTA) and 2% (w/v) polyvinylpyrrolidone (PVP). The entire extraction procedure was carried out at 4˚C. The homogenate was centrifuged at 10,000 g for 15 mn at 4˚C and the supernatant was collected and used for assaying enzyme activity.
Catalase (CAT, EC 1.11.1.6) activity was measured according to Bergmeyer & Gawehn (1970) [
Superoxide dismutase (SOD, EC 1.15.1.1) activity was assayed spectrophotometrically as the inhibition of photochemical reduction of nitro-blue tetrazolium (NBT) at 560 nm according to the method of Beauchamp & Fridovich (1971) [
Analysis of variance (ANOVA) was conducted on the data from the two experiments using PROC GLM of SAS 9.4 (SAS Institute Inc., Cary, NC). Replications were considered random and all other variables were considered fixed effects. Means of all variables were separated using Fisher’s protected LSD test.
There were significant differences between genotypes in their response to the type of salt solution and to the increase in salt concentration. Increasing salt concentrations significantly affected (p < 0.01) seed germination after two weeks in the 10 alfalfa genotypes (
Source of variation | Degrees of Freedom | Mean Squares |
---|---|---|
Genotypes | 9 | 1206.58** |
Salt solution | 1 | 33,606.67** |
Salt conc. | 3 | 75.87** |
Genotype Salt source | 9 | 70,772.34 |
Genotype & Salt Conc. | 27 | 298.00** |
Salt source & Salt conc. | 3 | 9109.41** |
Genotype & Salt source & Salt conc. | 27 | 338.81** |
Error | 180 |
*, ** Significant at 0.05 and 0.01 probability level.
Genotypes | NaCl (%) | Mixed (NaCl, MgCl2・6H2O and Na2SO4) (%) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
0 | 0.5 | 1.0 | 1.5 | 2.0 | 0 | 0.5 | 1.0 | 1.5 | 2.0 | |
3010 | 93.3 ± 2.3 | 66.7 ± 2.3 | 14.0 ± 2.0 | 3.0 ± 1.7 | 6.0 ± 2.0 | 93.3 ± 2.3 | 96.0 ± 0.0 | 92.0 ± 4.0 | 20.0 ± 4.0 | 0.0 ± 0.0 |
Bulldog505 | 82.0 ± 2.0 | 18.0 ± 2.0 | 4.0 ± 0.00 | 0.0 ± 0.0 | 0.0 ± 0.00 | 82.0 ± 2.0 | 74.0 ± 2.0 | 67.7 ± 0.6 | 3.7 ± 0.6 | 0.0 ± 0.0 |
Barricade | 92.0 ± 0.0 | 84.0 ± 4.0 | 22.7 ± 2.3 | 11.0 ± 1.0 | 0.0 ± 0.00 | 92.0 ± 0.0 | 93.3 ± 2.3 | 88.0 ± 4.0 | 16.7 ± 4.2 | 0.0 ± 0.0 |
CW1010 | 92.0 ± 6.9 | 82.7 ± 4.6 | 38.0 ± 2.0 | 7.7 ± 0.6 | 0.0 ± 0.0 | 92.0 ± 6.9 | 88.0 ± 4.0 | 85.3 ± 2.3 | 34.0 ± 3.5 | 0.0 ± 0.0 |
Hybriforce2600 | 90.0 ± 2.0 | 58.0 ± 2.0 | 16.3 ± 4.0 | 7.0 ± 1.0 | 3.7 ± 0.56 | 90.0 ± 2.0 | 86.7 ± 4.6 | 84.0 ± 4.0 | 18.0 ± 2.0 | 0.0 ± 0.0 |
Magna801FQ | 84.0 ± 0.0 | 84.0 ± 4.0 | 34.02.00 | 27.3 ± 8.1 | 0.0 ± 0.0 | 84.0 ± 0.0 | 84.7 ± 1.2 | 92.0 ± 8.0 | 25.3 ± 2.3 | 0.0 ± 0.0 |
Malone | 70.0 ± 10.0 | 66.0 ± 6.0 | 27.3 ± 1.2 | 0.0 ± 0.0 | 0.0 ± 0.0 | 70.0 ± 10.0 | 79.7 ± 0.6 | 73.3 ± 4.6 | 30.0 ± 2.0 | 0.0 ± 0.0 |
Mesa-Sirsa | 96.0 ± 0.0 | 86.0 ± 2.0 | 38.0 ± 2.0 | 28.0 ± 2.0 | 6.0 ± 0.0 | 96.0 ± 0.0 | 98.7 ± 2.3 | 93.3 ± 4.6 | 45.3 ± 3.1 | 6.0 ± 2.0 |
Rambler | 89.3 ± 2.3 | 50.7 ± 9.2 | 4.0 ± 0.0 | 0.0 ± 0.0 | 0.0 ± 0.0 | 89.3 ± 2.3 | 78.0 ± 2.0 | 38.7 ± 10.1 | 4.3 ± 0.6 | 0.0 ± 0.0 |
Sarance | 76.0 ± 0.0 | 66.0 ± 2.0 | 16.0 ± 4.0 | 0.0 ± 0.0 | 0.0 ± 0.0 | 76.0 ± 0.0 | 86.7 ± 6.1 | 78.0 ± 2.0 | 24.0 ± 4.0 | 3.3 ± 0.6 |
than the no-salt control (
An overall change in soil properties was observed at the end of the study, relative to the no-salt control (
Source | DF2 | pH | EC3 | CEC4 | Ca | K | Mg | P | Na | B | Zn | Fe | Mn |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Genotypes | 1 | 0.2** | 0.06 | 0.1 | 9960.4* | 197.9* | 379.9** | 1.2 | 453.7 | 0.1** | 0.1** | 4.1** | 0.01 |
Salt Conc. | 1 | 0.2** | 4.22** | 24.8** | 470,472.5** | 1141.0** | 256.2** | 2.2 | 181,838.3** | 0.1** | 0.2** | 0.01 | 0.0 |
Treatments1 | 2 | 0.01 | 0.54** | 0.2 | 8081.2** | 3375.5** | 28.5** | 1.6 | 485.9 | 0.01 | 0.2** | 0.2* | 0.2** |
Genotypes × Salt Conc. | 1 | 0.1** | 0.12 | 14.5** | 311,639.3** | 12,019.8** | 928.2** | 525.7** | 22,910.4** | 0.2** | 0.2** | 3.6** | 0.6** |
Genotypes × Treat | 2 | 0.001 | 0.05 | 1.8** | 36,539.3** | 253.4** | 40.2** | 78.8** | 1765.3* | 0.01 | 0.2 | 0.8** | 0.1** |
Salt Conc. × Treat | 2 | 0.01 | 1.24** | 13.0** | 263,097.3** | 8606.7** | 324.0** | 259.7** | 18,742.4** | 0.1** | 0.2 | 8.1** | 1.1** |
Genotypes × Salt Conc. × Treat | 2 | 0.04** | 0.46** | 7.8** | 125,630.1** | 6000.1** | 179.6** | 117.0** | 16,894.4** | 0.1** | 0.2 | 1.9** | 0.1** |
Error | 0.002 | 0.036 | 0.1 | 1043.7 | 44.7 | 3.4 | 2.4 | 363.9 | 0.01 | 0.01 | 0.1 | 0.0 | |
LSD5 | 0.03 | 0.120 | 0.2 | 20.4 | 4.2 | 1.2 | 1.0 | 12.1 | 0.1 | 0.1 | 0.2 | 0.1 |
*, **Significant at 0.05 and 0.01 probability level. 1Treatments: growth-enhancing substances (seaweed extract, humic acid, potassium sulfate). 2DF: Degrees of freedom. 3EC: Electrical conductivity in dS・m−1. 4CEC: Cation exchange capacity in meq 100 g−1 soil. 5LSD: Least significant difference at α = 0.05.
types at 10 dS・m−1 recording 69.4% with Bulldog, and 80.4% with Mesa-Sirsa, compared to no-salt control. Under 15 dS・m−1, seaweed extract increased the CEC of the soil under the susceptible genotype (Bulldog) recording 9.2 meq 100 g−1, while humic acid treatment recorded the highest CEC with the tolerant genotype (Mesa-Sirsa) with a value of 7.5 meq 100 g−1. The application of potassium sulfate resulted in accumulations of Ca, Mg, K, P, Na, B, Zn, Fe and Mn in the soil under both alfalfa genotypes at10 dS・m−1, while under 15 dS・m−1, seaweed extract resulted in accumulation of Ca, Mg, K, P, Na, B, Zn, Fe and Mn in the soil under both alfalfa genotypes.
Salt concentrations significantly affected (p < 0.01) the mineral composition of plant tissue in both genotypes and increased the Na/K ratio compared to the no-salt control (
There was a significant difference (p < 0.01) among the genotypes in Na/K and the concentration of Ca, Mg, N, S, Mn, Cu and Al in plant tissue. In the sensitive genotype, the application of potassium sulfate under salt stress at 10 dS・m−1 enhanced the uptake of K ions rather than Na+ ions leading to a lower Na/K compared to the other treatments. Humic acid treatment reduced the Na/K ratio under the higher salt concentration (15 dS・m−1). In the salt tolerant genotype, the Na/K ratio was lower than other treatments under the 10 dS・m−1 salt level,
Source | DF1 | Na/K | Ca | Mg | P | N | S | Fe | Zn | Mn | Cu | B | Al |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Genotypes | 1 | 73.7** | 8.1** | 0.1** | 0.001 | 1.8** | 0.04** | 100.9 | 2.8 | 316.5** | 0.75** | 15.1 | 90.04** |
Salt Conc. | 1 | 787.0** | 4.5** | 0.1** | 0.09** | 3.2** | 0.03** | 1840.4** | 193.3** | 63.5** | 6.7** | 90.57** | 1931.60** |
Treatments2 | 2 | 2.6 | 4.0** | 0.01 | 0.005 | 0.01 | 0.007* | 736.2** | 98.3** | 36.8** | 1.7** | 39.0** | 422.58** |
Genotypes × Salt Conc. | 1 | 38.8* | 6.8** | 0.00002 | 0.001 | 1.9** | 0.04 | 20.3 | 0.79 | 36.4** | 0.01 | 20.1* | 67.51** |
Genotypes × Treatments | 2 | 43.2** | 0.3 | 0.001 | 0.01** | 0.09 | 0.02** | 54.7 | 3.0 | 64.5** | 1.6** | 40.5** | 340.39** |
Salt Conc. × Treatments | 2 | 23.9* | 0.5** | 0.003 | 0.00003 | 0.01 | 0.008* | 329.6** | 2.4 | 46.3** | 0.78** | 5.1 | 452.07** |
Germpl × Salt Conc. × Treatments | 2 | 23.4* | 1.4 | 0.005 | 0.009* | 0.3** | 0.0003 | 434.01** | 44.7 | 70.3** | 3.04** | 42.1** | 383.63** |
Error | 6.23 | 0.5 | 0.004 | 0.002 | 0.05 | 0.002 | 31.32 | 2.49 | 5.24 | 0.09 | 4.70 | 3.39 | |
LSD3 | 1.58 | 1.4 | 0.12 | 0.09 | 0.4 | 0.086 | 3.54 | 1.00 | 1.45 | 0.19 | 1.37 | 1.16 |
*, **Significant at 0.05 and 0.01 probability level. 1DF: Degrees of freedom. 2Treatments: seaweed extract, humic acid, and potassium sulfate. 3LSD: Least significant difference at α = 0.05.
following the application of humic acid, whereas under the higher salt level (15 dS・m−1), the application of seaweed extract resulted in the lowest Na/K ratio (
high concentrations of total phenolics, a complex group known for its strong chelating activities [
Salt concentrations had significant effects (p < 0.01) on shoot and root dry weights. Plant biomass was reduced under both salt concentrations in both genotypes, with a greater magnitude in the salt-sensitive Bulldog 505, compared with the no-salt control (
Source of variation | Degrees of freedom | Shoot dry weight | Plant height | Root length | Root dry weight |
---|---|---|---|---|---|
Genotype | 1 | 0.1* | 1.3 | 168.7* | 3.6** |
Salt level | 1 | 1.01** | 32.4** | 0.1 | 1.8* |
Genotype × Salt level | 1 | 0.001 | 15.3* | 12.5 | 0.004 |
Treatments | 2 | 0.1* | 4.9 | 0.04 | 0.004 |
Genotype × Treatments | 2 | 0.1* | 7.51 | 25.0 | 1.8* |
Salt level × Treatments | 2 | 0.02 | 0.4 | 0.2 | 0.1 |
Genotype × Treatments × Salt levels | 2 | 0.2** | 19.3** | 5.5 | 0.1 |
Error | 28 | 0.02 | 2.6 | 23.8 | 0.3 |
LSD | 0.1 | 1.02 | 3.1 | 0.3 |
*, **Significant at 0.05 and 0.01 probability level.
Genotype | Salt level | Treatments | Shoot dry weight (g) | Plant height (cm) | Root length (cm) | Root dry weight (g) |
---|---|---|---|---|---|---|
Bulldog 505 | Control (0 salt ) | Control ( 0 salt ) | 2.49 ± 0.18 | 32.38 ± 1.68 | 29.88 ± 7.65 | 3.67 ± 0.49 |
10 dS・m−1 | Seaweed extract | 1.68 ± 0.20 | 19.86 ± 0.91 | 21.05 ± 2.51 | 2.97 ± 0.71 | |
Humic acid | 1.67 ± 0.11 | 22.35 ± 2.15 | 20.22 ± 4.54 | 2.04 ± 0.15 | ||
Potassium sulfate | 1.40 ± 0.11 | 20.45 ± 1.91 | 23.33 ± 6.78 | 2.92 ± 0.60 | ||
15 dS・m−1 | Seaweed extract | 1.19 ± 0.10 | 19.78 ± 1.51 | 18.94 ± 2.46 | 2.24 ± 0.59 | |
Humic acid | 1.16 ± 0.15 | 18.66 ± 2.47 | 20.49 ± 10.01 | 1.84 ± 0.50 | ||
Potassium sulfate | 1.42 ± 0.03 | 22.44 ± 1.39 | 21.96 ± 7.12 | 2.44 ± 0.93 | ||
Mesa-Sirsa | Control (0 salt ) | Control ( 0 salt ) | 2.02 ± 0.11 | 27.11 ± 2.07 | 20.32 ± 3.91 | 2.34 ± 0.39 |
10 dS・m−1 | Seaweed extract | 1.47 ± 0.14 | 24.26 ± 0.42 | 18.28 ± 1.47 | 2.08 ± 0.47 | |
Humic acid | 1.76 ± 0.04 | 24.57 ± 2.28 | 19.18 ± 2.83 | 2.67 ± 0.44 | ||
Potassium sulfate | 1.56 ± 0.34 | 24.51 ± 0.71 | 16.40 ± 2.65 | 2.05 ± 0.44 | ||
15 dS・m−1 | Seaweed extract | 1.23 ± 0.09 | 20.41 ± 1.88 | 21.16 ± 2.52 | 1.67 ± 0.12 | |
Humic acid | 1.49 ± 0.10 | 23.82 ± 0.47 | 19.05 ± 1.67 | 2.29 ± 0.16 | ||
Potassium sulfate | 1.03 ± 0.07 | 19.50 ± 0.57 | 17.51 ± 1.66 | 1.55 ± 0.30 |
nutrients (
1) Relative water content (RWC)
Relative water content is an index describing the amount of water in plant tissue and indicates the ability of a plant to maintain adequate water under stress conditions [
Source of variation | Degrees of Freedom | RWC | Electrolyte leakage | Proline |
---|---|---|---|---|
Genotype | 1 | 15.71 | 1358.73** | 1.17** |
Salt level | 1 | 116.17** | 24.24** | 1.31** |
Genotype × Salt level | 1 | 119.65** | 24.59** | 0.75* |
Treatments | 2 | 47.22** | 275.42** | 0.11 |
Genotype × Treatments | 2 | 41.99** | 340.77** | 2.71** |
Salt level × Treatments | 2 | 110.31** | 219.74** | 3.96** |
Genotype × Treatments × Salt levels | 2 | 37.33** | 239.85** | 1.86** |
Error | 28 | 4.02 | 2.39 | 0.166 |
LSD | 1.27 | 0.98 | 0.26 |
*, **Significant at 0.05 and 0.01 probability level.
Genotype | Salt level | Treatments | RWC (%) | Electrolyte leakage (%) | Proline (µmol・g−1 FW) |
---|---|---|---|---|---|
Bulldog 505 | Control (0 salt) | Control (0 salt) | 48.10 ± 0.41 | 51.03 ± 3.32 | 2.90 ± 0.74 |
10 dS・m−1 | Seaweed extract | 43.51 ± 0.63 | 63.29 ± 0.53 | 2.08 ± 0.87 | |
Humic acid | 43.47 ± 3.2 | 81.84 ± 0.73 | 2.27 ± 0.04 | ||
Potassium sulfate | 31.65 ± 0.10 | 76.40 ± 1.34 | 3.16 ± 0.30 | ||
15 dS・m−1 | Seaweed extract | 42.74 ± 0.53 | 65.57 ± 1.78 | 3.61 ± 0.50 | |
Humic acid | 34.43 ± 1.29 | 69.50 ± 1.01 | 1.98 ± 0.49 | ||
Potassium sulfate | 41.63 ± 0.85 | 80.43 ± 1.14 | 2.20 ± 0.36 | ||
Mesa-Sirsa | Control (0 salt ) | Control (0 salt) | 46.28 ± 0.07 | 74.45 ± 0.87 | 1.83 ± 0.14 |
10 dS・m−1 | Seaweed extract | 44.71 ± 1.21 | 81.43 ± 0.22 | 1.58 ± 0.21 | |
Humic acid | 46.03 ± 3.53 | 87.96 ± 1.69 | 2.06 ± 0.21 | ||
Potassium sulfate | 45.77 ± 5.05 | 87.46 ± 0.24 | 2.67 ± 0.20 | ||
15 dS・m−1 | Seaweed extract | 34.42 ± 0.22 | 75.85 ± 1.86 | 2.44 ± 0.17 | |
Humic acid | 39.66 ± 1.79 | 81.35 ± 1.45 | 4.12 ± 0.25 | ||
Potassium sulfate | 40.71 ± 0.38 | 83.57 ± 2.27 | 1.76 ± 0.27 |
Mesa-Sirsa, the highest RWC was achieved by the addition of humic acid under 10 dS・m−1 (46.03%) and K2SO4 nanoparticles under 15 dS・m−1 (40.71%). The increase in the RWC following the application of humic acid may be attributed to enhanced root biomass (root length and dry weight) that leads to absorbing more water under salt stress, while potassium acts as an osmo-regulator in the cell [
2) Electrolyte leakage
Electrolyte leakage (EL) is an indirect assessment of the degree of cell membrane integrity [
3) Proline
Proline accumulation is a sensitive physiological index of plant response to various abiotic stresses [
4) Proline
Proline accumulation is a sensitive physiological index of plant response to various abiotic stresses [
There was a significant difference (p < 0.01) between the genotypes in their CAT activity following the increase in salt concentrations and the application of growth stimulant treatments (
Source of variation | DF | Catalase | SOD |
---|---|---|---|
Genotype | 1 | 1589.75** | 51.91 |
Salt level | 1 | 1664.23** | 25.39 |
Genotype × Salt level | 1 | 97.19** | 109.51 |
Treatments | 2 | 1839.25** | 811.36** |
Genotype × Treatments | 2 | 163.70** | 355.18* |
Salt level × Treatments | 2 | 964.24** | 697.71** |
Genotype × Treatments × Salt levels | 2 | 436.50** | 261.06** |
Error | 28 | 5.73 | 77.94 |
LSD | 1.51 | 5.58 |
*, **Significant at 0.05 and 0.01 probability level.
Potassium sulfate resulted in the highest increases in SOD activity in both genotypes under the 15 dS・m−1 salt level, but was not much different from seaweed extract (
There is evidence that seaweed extract increases tolerance to oxidative stress and protects against adverse environmental conditions by enhancing the activity of the antioxidant enzymes SOD and Ascorbate peroxidase (ASP) [
There was a significant positive correlation (r = 0.42, p < 0.01) between proline content in the plant tissue and relative water content (
Shoot dry weight | Plant height | Root length | Root dry weight | Relative Water Content | Electrolyte leakage | Proline | CAT | SOD | |
---|---|---|---|---|---|---|---|---|---|
Shoot dry weight | 1.00 | 0.76** | 0.24 | 0.62** | 0.57** | −0.03 | 0.003 | 0.34* | 0.50** |
Plant height | - | 1.00 | 0.2 | 0.35 | 0.57** | −0.07 | −0.04 | 0.37* | 0.55** |
Root length | - | - | 1.00 | 0.44** | 0.04 | −0.29 | 0.05 | 0.05 | −0.08 |
Root dry weight | - | - | - | 1.00 | 0.19 | −0.08 | 0.19 | 0.22 | 0.17 |
Relative Water Content | - | - | - | - | 1.00 | −0.04 | 0.42** | −0.28 | 0.44** |
Electrolyte leakage | - | - | - | - | - | 1.00 | −0.18 | −0.40** | 0.33 |
Proline | - | - | - | - | - | - | 1.00 | 0.14 | 0.17 |
CAT | - | - | - | - | - | - | - | 1.00 | 0.47** |
SOD | - | - | - | - | - | - | - | - | 1.00 |
well as a source of energy [
Increasing salt concentration reduced germination in all alfalfa genotypes. Above 1% salt in the solution reduced seed germination by more than 70% in most genotypes. Growing alfalfa plants under salt concentration of 10 dS・m−1 and above, resulted in significant decreases in plant shoot and root growth, with a lesser magnitude in salt tolerant genotypes. Application of plant growth stimulants (seaweed extract, humic acid, and potassium sulfate) to one salt tolerant and one salt sensitive genotype grown under two salt levels (10 and 15 dS・m−1) resulted in overall changes in soil properties relative to the no-salt control. Application of humic acid improved the growth of the salt-tolerant genotype under both salt concentrations, while seaweed extract and potassium sulfate were more effective in the salt sensitive genotype under 10 and 15 dS・m−1. Overall, potassium sulfate was more effective in maintaining a low Na/K ratio in the susceptible genotype under 10 dS・m−1 and humic acid under 15 dS・m−1, while in the salt tolerant genotype, humic acid was more effective in maintaining a low Na/K ratio under 10 dS・m−1 and seaweed extract under 15 dS・m−1. Seaweed extract resulted in higher RWC and proline under both salt concentrations (10 and 15 dS・m−1) in the salt sensitive genotype and lower electrolyte leakage in both salt tolerant and salt sensitive genotypes under both salt concentrations. Seaweed extract also enhanced CAT and SOD activities in both genotypes under 10 dS・m−1. Application of seaweed extract seemed to have an overall positive effect in alleviating salt stress in the salt-sensitive alfalfa genotype, while the application of humic acid and potassium sulfate seemed to have an overall positive effect in maintaining growth under salt stress in the salt-tolerant alfalfa genotype.
El-Sharkawy, M., El-Beshsbeshy, T., Al-Shal, R. and Missaoui, A. (2017) Effect of Plant Growth Sti- mulants on Alfalfa Response to Salt Stress. Agricultural Sciences, 8, 267-291. https://doi.org/10.4236/as.2017.84020