Algal Bio-Stimulants Enhance Salt Tolerance in Common Bean: Dissecting Morphological, Physiological, and Genetic Mechanisms for Stress Adaptation

Abstract

Salinity adversely affects the plant's morphological characteristics, but the utilization of aqueous algal extracts (AE) ameliorates this negative impact. In this study, the application of AE derived from Chlorella vulgaris and Dunaliella salina strains effectively reversed the decline in biomass allocation and water relations, both in normal and salt-stressed conditions. The simultaneous application of both extracts in salt-affected soil notably enhanced key parameters, such as chlorophyll content (15%), carotene content (1%), photosynthesis (25%), stomatal conductance (7%), and transpiration rate (23%), surpassing those observed in the application of both AE in salt-affected as compared to salinity stress control. Moreover, the AE treatments effectively mitigated lipid peroxidation and electrolyte leakage induced by salinity stress. The application of AE led to an increase in GB (6%) and the total concentration of free amino acids (47%) by comparing with salt-affected control. Additionally, salinity stress resulted in an elevation of antioxidant enzyme activities, including superoxide dismutase, ascorbate peroxidase, catalase, and glutathione reductase. Notably, the AE treatments significantly boosted the activity of these antioxidant enzymes under salinity conditions. Furthermore, salinity reduced mineral contents, but the application of AE effectively counteracted this decline, leading to increased mineral levels. In conclusion, the application of aqueous algal extracts, specifically those obtained from Chlorella vulgaris and Dunaliella salina strains, demonstrated significant efficacy in alleviating salinity-induced stress in Phaseolus vulgaris plants.

Keywords: Chlorella vulgaris; Dunaliella salina; Phaseolus vulgaris; antioxidants; osmolytes; photosynthesis; salinity.

Figure 1

Effect of Chlorella vulgaris and Dunaliella salina extracts on (A) plant height, (B) leaf area, (C) shoot fresh weight, (D) root fresh weight, (E) shoot dry weight, (F) root dry weight in common bean plants under normal and saline condition soils. On x-axis NC; normal soil control, SC; salt-affected soil control, Exc; extract of Chlorella vulgaris, Exd; extract of Dunaliella salina, Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in normal soil, S + Exc; application of Chlorella vulgaris in salt-affected soil, S + Exd; application of Dunaliella salina in salt-affected soil, S + Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in salt-affected soil. Bar chart presenting mean values of different treatments, error bars indicating standard deviation, and different lettering on the bars highlighting the significance difference among the applied treatments at a 5% level of significance by applying Duncan’s Multiple Range Test (DMRT).

Figure 2

Effect of Chlorella vulgaris and Dunaliella salina extracts on (A) biomass allocation (Shoot: Root ratio), (B) relative water content, (C) Leaf water potential (LWP; MPa), (D) WUE, and (E) The transpiration rate (Tr, mmol m⁻² s⁻¹) in common bean plants under normal and saline condition soils. On x-axis NC; normal soil control, SC; salt-affected soil control, Exc; extract of Chlorella vulgaris, Exd; extract of Dunaliella salina, Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in normal soil, S + Exc; application of Chlorella vulgaris in salt-affected soil, S + Exd; application of Dunaliella salina in salt-affected soil, S + Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in salt-affected soil. Bar chart presenting mean values of different treatments, error bars indicating standard deviation, and different lettering on the bars highlighting the significance difference among the applied treatments at a 5% level of significance by applying Duncan’s Multiple Range Test (DMRT).

Figure 3

Effect of Chlorella vulgaris and Dunaliella salina extracts on (A) Leaf chlorophyll contents, (B) Carotenoids, (C) Photosynthetic rate (Pn), (D) Leaf stomatal conductance (Gs) in common bean plants under normal and saline condition soils. On x-axis NC; normal soil control, SC; salt-affected soil control, Exc; extract of Chlorella vulgaris, Exd; extract of Dunaliella salina, Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in normal soil, S + Exc; application of Chlorella vulgaris in salt-affected soil, S + Exd; application of Dunaliella salina in salt-affected soil, S + Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in salt-affected soil. Bar chart presenting mean values of different treatments, error bars indicating standard deviation, and different lettering on the bars highlighting the significance difference among the applied treatments at a 5% level of significance by applying Duncan’s Multiple Range Test (DMRT).

Figure 4

Effect of Chlorella vulgaris and Dunaliella salina extracts on (A) Cellular lipid peroxidation (MDA; nmol g⁻¹ FW), (B) Hydrogen peroxide (H₂O₂; µmol g⁻¹ FW), (C) Electrolyte leakage (EL; %) in common bean plants under normal and saline condition soils. On x-axis NC; normal soil control, SC; salt-affected soil control, Exc; extract of Chlorella vulgaris, Exd; extract of Dunaliella salina, Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in normal soil, S + Exc; application of Chlorella vulgaris in salt-affected soil, S + Exd; application of Dunaliella salina in salt-affected soil, S + Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in salt-affected soil. Bar chart presenting mean values of different treatments, error bars indicating standard deviation, and different lettering on the bars highlighting the significance difference among the applied treatments at a 5% level of significance by applying Duncan’s Multiple Range Test (DMRT).

Figure 5

Effect of Chlorella vulgaris and Dunaliella salina extracts on (A) Glycine betaine (GB; µmol/g FW), (B) Proline content (µmol/g FW), (C) total soluble sugars (mg/100 g DW), (D) Total protein content (mg/100 g DW), (E) total free amino acids (TFAA, mg/100 g DW) in common bean plants under normal and saline condition soils. On x-axis NC; normal soil control, SC; salt-affected soil control, Exc; extract of Chlorella vulgaris, Exd; extract of Dunaliella salina, Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in normal soil, S + Exc; application of Chlorella vulgaris in salt-affected soil, S + Exd; application of Dunaliella salina in salt-affected soil, S + Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in salt-affected soil. Bar chart presenting mean values of different treatments, error bars indicating standard deviation, and different lettering on the bars highlighting the significance difference among the applied treatments at a 5% level of significance by applying Duncan’s Multiple Range Test (DMRT).

Figure 6

Effect of Chlorella vulgaris and Dunaliella salina extracts on (A) Ascorbic acid (AsA; µmol g⁻¹ FW), (B) Reduced Glutathione (GSH; nmol/g FW), (C) Superoxide dismutase activities (SOD; U/g FW), (D) Catalase activities (CAT; U/g FW), (E) Ascorbic peroxidase (APX; U/g FW), and (F) glutathione reductase (GR; U/g FW) in common bean plants under normal and saline condition soils. On x-axis NC; normal soil control, SC; salt-affected soil control, Exc; extract of Chlorella vulgaris, Exd; extract of Dunaliella salina, Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in normal soil, S + Exc; application of Chlorella vulgaris in salt-affected soil, S + Exd; application of Dunaliella salina in salt-affected soil, S + Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in salt-affected soil. Bar chart presenting mean values of different treatments, error bars indicating standard deviation, and different lettering on the bars highlighting the significance difference among the applied treatments at a 5% level of significance by applying Duncan’s Multiple Range Test (DMRT).

Figure 7

Effect of Chlorella vulgaris and Dunaliella salina extracts on (A) N (g/kg DW), (B) P (g/kg DW), (C) K (g/kg DW), (D) Na (g/kg DW), (E) Ca (g/kg DW), (F) Mg (g/kg DW) in common bean plants under normal and saline condition soils. On x-axis NC; normal soil control, SC; salt-affected soil control, Exc; extract of Chlorella vulgaris, Exd; extract of Dunaliella salina, Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in normal soil, S + Exc; application of Chlorella vulgaris in salt-affected soil, S + Exd; application of Dunaliella salina in salt-affected soil, S + Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in salt-affected soil. Bar chart presenting mean values of different treatments, error bars indicating standard deviation, and different lettering on the bars highlighting the significance difference among the applied treatments at a 5% level of significance by applying Duncan’s Multiple Range Test (DMRT).

Figure 8

Effect of Chlorella vulgaris and Dunaliella salina extract on Relative gene expression of (A) PIP1 Aquaporin gene, (B) Osmotin-34, (C) SOS1, (D) NHX1 in common bean plants under normal and saline condition soils. On x-axis NC; normal soil control, SC; salt-affected soil control, Exc; extract of Chlorella vulgaris, Exd; extract of Dunaliella salina, Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in normal soil, S + Exc; application of Chlorella vulgaris in salt-affected soil, S + Exd; application of Dunaliella salina in salt-affected soil, S + Exc + Exd; combined application of Chlorella vulgaris and Dunaliella salina in salt-affected soil. Bar chart presenting mean values of different treatments, error bars indicating standard deviation, and different lettering on the bars highlighting the significance difference among the applied treatments at a 5% level of significance by applying Duncan’s Multiple Range Test (DMRT).

Figure 9

Correlation matrix showing the interaction between different study variables in terms of Pearson’s correlation, where blue color indicates positive correlation, red color for inverse (−) correlation, and boxed colors indicate significant correlation.

Figure 10

Canonical correspondence analysis showing the effect of salinity, (Ext1 represents EXc; and Ext2 represents EXd) on various variables.