Arbuscular mycorrhizal fungi enhance tolerance of vinca to high alkalinity in irrigation water

This study was conducted in order to determine if inoculation with arbuscular mycorrhizal fungi (AMF) would enhance the tolerance of vinca plants to high levels of alkalinity, induced by KHCO₃, in irrigation water. AMF-inoculated and non-inoculated plants were irrigated with water containing varying HCO₃⁻ concentrations: 0, 2.5, 5, 7.5, 10, and 15 mM. Increased HCO₃⁻ concentration inhibited plant growth, specifically at concentrations ≥7.5 mM. Leaves were more affected by high HCO₃⁻ concentration than other plant parts. In non-inoculated plants, a visual evaluation of quality demonstrated that acceptable quality was produced when irrigation water contained ≤2.5 mM HCO₃⁻, but AMF-inoculated plants of good quality were produced when irrigation water contained ≤7.5 mM HCO₃⁻. In general, AMF alleviated HCO₃⁻ stress, as indicated by greater plant growth and ranking of quality. However, AMF-inoculated plants irrigated with 0 mM HCO₃⁻ exhibited reduced growth when compared to non-inoculated plants. Bicarbonate did not affect leaf Fe concentration, indicating that vinca may be a Fe efficient plant. Plants inoculated with AMF exhibited an enhanced leaf P concentration and content, which was related to an increase in the activity of the soluble alkaline phosphatase. Plants inoculated with AMF exhibited increased leaf concentration and content of Mn, Zn, Cu, B, and Mo, and increased antioxidant activity under high concentrations of HCO₃⁻. In conclusion, the tolerance of vinca to alkalinity in irrigation water can be enhanced by AMF inoculation, thus, allowing for irrigation with water of high alkalinity.