Additive and synergistic effects of mycorrhizal inoculants and fertilizer in enhancing chard (Beta vulgaris) growth under glasshouse cultivation

Abstract

Mycorrhizal fungi and fertilizers are widely used to enhance crop productivity, yet their relative contributions and the interactions of biostimulants and fertilizers remain unclear. In this study, we assessed the impact of five individual arbuscular mycorrhizal (AM) fungal strains, a fungal mixture, and fertilizer on chard (Beta vulgaris) growth using a fully factorial greenhouse experiment. Results showed that while fertilizer alone increased biomass by 32%, mycorrhizal inoculation alone resulted in −35% to + 43% more chard biomass, depending on the fungal species. The combination of fertilizer and inoculant increased biomass by 33–81% compared to non-fertilized controls, and by 0–36% relative to fertilized controls. Fungal responses varied: Gigaspora gigantea suppressed growth in the absence of fertilizer but showed synergistic benefits when paired with it. In contrast, Rhizophagus irregularis and the five-species fungal mixture consistently enhanced growth across nutrient conditions. Overall, the combined effects of fertilization and inoculation were largely additive. These results highlight the context-dependent nature of AM fungal benefits and suggest that certain strains can complement or be a substitute for synthetic fertilizers in sustainable cultivation systems.