Enhancing sweet potato (Ipomoea batatas) resilience grown in cadmium-contaminated saline soil: a synergistic approach using Moringa leaf extract and effective microorganisms application

Abstract

Raising soil contamination with cadmium (Cd²⁺) and salinization necessitates the development of green approaches using bio-elicitors to ensure sustainable crop production and mitigate the detrimental health impacts. Two field trials were carried out to study the individual and combined effects of foliage spraying of Moringa leaf extract (MLE) and soil application of effective microorganisms (EMs) on the physio-biochemical, osmolytes, antioxidants, and performance of sweet potato grown in Cd²⁺-contaminated salty soil (Cd²⁺ = 17.42 mg kg^-1 soil and soil salinity ECe = 7.42 dS m^-1). Application of MLE, EMs, or MLE plus EMs significantly reduced the accumulation of Cd²⁺ in roots by 55.6%, 50.0%, or 68.1% and in leaves by 31.4%, 27.6%, or 38.0%, respectively, compared to the control. Co-application of MLE and EMs reduced Na⁺ concentration while substantially raising N, P, K⁺, and Ca²⁺ acquisition in the leaves. MLE and EMs-treated plants exhibited higher concentrations of total soluble sugar by 69.6%, free proline by 47.7%, total free amino acids by 29.0%, and protein by 125.7% compared to the control. The enzymatic (SOD, APX, GR, and CAT) and non-enzymatic (phenolic acids, GSH, and AsA) antioxidants increased in plants treated with MLE and/or EMs application. Applying MLE and/or EMs increased the leaf photosynthetic pigment contents, membrane stability, relative water content, water productivity, growth traits, and tuber yield of Cd²⁺ and salt-stressed sweet potato. Consequently, the integrative application of MLE and EMs achieved the best results exceeding the single treatments recommended in future application to sweet potato in saline soil contaminated with Cd²⁺.

Keywords: Biostimulants; Growth and productivity; Heavy metals; Osmoprotectants; Phytotoxicity; Salinity.

Fig. 1

Influence of Moringa leaf extract (MLE) and effective microorganisms (EMs) on osmolytes (i.e., free proline, total free amino acids—TFA, total soluble sugars—TSS, and soluble proteins) content of sweet potato plants grown in Cd2 + -contaminated saline soil in the 2020 and 2021 seasons (as average). The various lower-case letters on the bar distinguished the treatments, corresponding to Fisher’s test at p ≤ 0.05

Fig. 2

Influence of Moringa leaf extract (MLE) and effective microorganisms (EMs) on the activity of glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) of sweet potato plants grown in Cd2 + -contaminated saline soil in the 2020 and 2021 seasons (as average). The various lower-case letters on the bar distinguished the treatments, corresponding to Fisher’s test at p ≤ 0.05

Fig. 3

Influence of Moringa leaf extract (MLE) and effective microorganisms (EMs) on phenolic acids, ascorbic acid (AsA), and glutathione (GSH) contents of sweet potato plants grown in Cd2 + -contaminated saline soil in the 2020 and 2021 seasons (as average). The various lower-case letters on the bar distinguished the treatments, corresponding to Fisher’s test at p ≤ 0.05

Fig. 4

Influence of Moringa leaf extract (MLE) and effective microorganisms (EMs) on leaf nutrient concentrations of sweet potato grown in Cd2 + -contaminated saline soil in the 2020 and 2021 seasons (as average). The various lower-case letters on the bar distinguished the treatments, corresponding to Fisher’s test at p ≤ 0.05

Fig. 5

Influence of Moringa leaf extract (MLE) and effective microorganisms (EMs) on the Cd2 + content in roots and leaves of sweet potato grown in Cd2 + -contaminated saline soil in the 2020 and 2021 seasons (as average). The various lower-case letters on the bar distinguished the treatments, corresponding to Fisher’s test at p ≤ 0.05

Fig. 6

The heat map diagram displays hierarchical clustering analysis among the application of Moringa leaf extract (MLE) and/or effective microorganisms (EMs) and different studied parameters of sweet potato plants grown Cd2 + -contaminated saline soil. SOD, superoxide dismutase; RWC, relative water content; AsA, ascorbic acid; MSI, membrane stability index; CAT, catalase; APX, ascorbate peroxidase; GR, glutathione reductase; Leaf.area, leaf area plant⁻¹; K, potassium; P, phosphorus; N, nitrogen; Ca, calcium; Na, sodium; Shoot DW, shoot dry weight; TSS, total soluble sugars; Tubers. no. plant, tubers number plant-1; GSH, glutathione; Cd. root and Cd. Leaves, roots and leaves Cd2 + content, respectively

Fig. 7

Biplot of the principal component analysis (PCA) illustrating the relationship among the effects of Moringa leaf extract (MLE) and/or effective microorganisms (EMs) on different assessed parameters of sweet potato plants grown in Cd2 + -contaminated saline soil. Ca, calcium; Na, sodium; proline, free proline; TSS, total soluble sugars; GSH, glutathione; Shoot DW, shoot dry weight; Cd root and Cd leaves, roots and leaves Cd2 + content, respectively