Soil Nutritional Status Drives the Co-occurrence of Nodular Bacterial Species and Arbuscular Mycorrhizal Fungi Modulating Plant Nutrition and Growth of Vigna unguiculataL. (Walp) in Grassland and Savanna Ecosystems in KwaZulu-Natal, South Africa

Vigna unguiculatais a staple food with high nutritional value and commonly consumed among many rural communities in South Africa. Its success in low nutrient soil has been attributed to the establishment of efficient symbioses with soil bacteria and fungi. We investigated how legume-microbe symbiosis affect nitrogen (N) nutrition, and growth of V. unguiculatagrown in nutrient-deficient soils of KwaZulu-Natal (KZN). Seeds of four V. unguiculataL. (Walp) varieties (IT18, Batch white, Brown mix, Dr Saunders) commonly grown by local farmers in South Africa were used in this study. The seeds were grown in nutrient-poor natural soils collected from four geographically different areas in KZN, under glasshouse conditions. From each site, homogenized soils were analyzed for soil nutrient concentration, soil chemistry, and arbuscular mycorrhizal (AM) fungal spore count. V. unguiculatawas nodulated by several bacterial strains including Bradyrhizobium, Rhizobium, Paenibacillus, and Bacillusstrains. The legume effectively fixed more than 60% of its total N from the atmosphere in all soil treatments. The V. unguiculatavarieties had symbiotic association with arbuscular mycorrhizal fungi (AMF). The AMF root colonization ranged from 58 to 100%, with Hluhluwe soil–grown plants recording the highest for all V. unguiculatavarieties. There were variations in growth kinetics, nutrient assimilation, and utilization among the four V. unguiculatavarieties grown in the soil types. All the V. unguiculatavarieties utilized both soil and atmospheric N and they maintained their total plant N concentrations despite the differences in soil nutrient properties. The current findings revealed that V. unguiculatamay adapt to nutrient-poor ecosystems by establishing symbiotic interaction with naturally occurring soil bacteria and AMF and through its ability to switch N source preferences.