Salt Tolerance Strategies of Nitraria tangutorum Bobr. and Elaeagnus angustifolia Linn. Determine the Inoculation Effects of Microorganisms in Saline Soil Conditions

Abstract

Increasing salinization threatens the normal growth of halophytes in saline habitats, especially at the seedling stage. Soil beneficial microorganisms have the potential to promote salt tolerance of halophytes, but less attention has been paid to the various responses between different halophytes with microbial inoculations. Here we performed pot experiments to assess the responses of Nitraria tangutorum Bobr. and Elaeagnus angustifolia Linn. to arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) inoculation in saline soil conditions. The results showed that neither a single AMF inoculation nor a single PGPR inoculation promoted the growth of N. tangutorum. In contrast, co-inoculation not only promoted biomass accumulation but also promoted the absorption of P, K+, and Ca2+ in the roots, and the accumulation of N, Na+, K+, and Ca2+ in the leaves. Co-inoculation also increased the K+/Na+ ratio in the roots as well as the Ca2+/Na+ ratio in both roots and leaves of N. tangutorum. Na+ is an important inorganic osmolyte, essential for both efficient osmoregulation and biomass accumulation in N. tangutorum. PGPR inoculation alone could not promote the growth of E. angustifolia. AMF inoculation, solely or combined with PGPR, was beneficial to the absorption of K+ and Ca2+ in the roots, the accumulation of N and K+ in the leaves, the maintenance of the K+/Na+ ratio and Ca2+/Na+ ratio in the leaves, the selective transportation of K+ and Ca2+ from roots to leaves, and the accumulation of proline and glycine betaine in the leaves of E. angustifolia. Increased nutrient absorption, ion homeostasis, and K+ and Ca2+ selective transportation in AMF-inoculated E. angustifolia helped reduce the toxic effects of Na+ and the damage caused by osmotic stress in saline soil conditions. “Plant-microbe specificity” leads to the different responses of N. tangutorum and E. angustifolia seedlings to AMF and PGPR inoculation in saline soil conditions. The different salt tolerance strategies for osmoregulation, nutrient acquisition, ion homeostasis, and ion transportation determine the differential responses in N. tangutorum and E.angustifolia to AMF and PGPR inoculations under saline soil conditions.