Phenolic Acids and Plant Antioxidant Capacity Enhance Growth, Nutrition, And Plant-Microbe Interaction of Vigna unguiculata L. (Walp) Grown in Acidic and Nutrient-Deficient Grassland and Savanna Soils

Soil acidity and nutrient stress are the major abiotic factors affecting crop production thus contributing to food insecurity. Some plants including crop legumes may thrive in such poor conditions by regulating their secondary metabolites. In this study, we investigated how four Vigna unguiculata varieties regulated their phenolic acid concentrations and antioxidant capacities to better adapt to acidic and nutrient-deficient grassland and savanna ecosystems. Four V. unguiculata varieties (IT18, Batch white, Brown mix, and Dr Saunders) were grown in soils collected from four geographically distinct areas (Bergville, Ashburton, Izingolweni, Hluhluwe) in KwaZulu-Natal covering grassland and savanna ecosystems. Plants were analyzed for nutrient composition, arbuscular mycorrhizal fungi colonization percentage, and root-nodulating bacteria. Oxygen radical absorbance capacity and phenolic acid concentrations were also determined. There were differences in plant biomass, nitrogen, and phosphorus nutrition across the four V unguiculata varieties, with high arbuscular mycorrhizal fungi colonization of greater than 58%. V. unguiculata was nodulated by several bacterial strains including Bacillus, Paenibacillus, Delftia, Rhizobium, and Bradyrhizobium. All four V. unguiculata varieties had variations in phenolic acids across all soil types with vanillic acid and protocatechuic acid being the most abundant, constituting 22.59% and 17.22%, respectively, of the total phenolic acids. Principal component analysis also showed differences in phenolic acid production across the four V. unguiculata varieties. There were variations in correlations between the phenolic acids and plant biomass, plant nutrition, soil nutrition, and arbuscular mycorrhizal fungi infection. Varieties IT18 and Batch white had relatively higher oxygen radical absorbance capacity across the four soil types and comparably higher plant biomass relative to Brown mix and Dr Saunders. Overall, the current findings demonstrated that V. unguiculata has the potential of adapting to acidic and nutrient-stressed grassland and savanna conditions through production of phenolic acids and enhanced antioxidant capacity.

Automated summary

This study investigates how four varieties of Vigna unguiculata adapt to acidic and nutrient-deficient grassland and savanna ecosystems by regulating their phenolic acid concentrations and antioxidant capacities. The study finds variations in phenolic acids across all soil types and differences in correlations between the phenolic acids and plant biomass, plant nutrition, soil nutrition, and arbuscular mycorrhizal fungi infection. Varieties IT18 and Batch white show relatively higher antioxidant capacity and plant biomass compared to Brown mix and Dr Saunders.