Arbuscular mycorrhizal symbiosis improves growth and root nutrient status of citrus subjected to salt stress

The application of microorganisms such as arbuscular mycorrhizal fungi to enhance salt resistance is quite well-known, but the interaction of mycorrhiza and salinity to growth, relative water content, and nutrient concentrations of salt-sensitive citrus (Citrus tangerine) seedlings has been less studied. The non-colonized seedlings and seedlings colonized by Glomus mosseae or Paraglomus occultum were exposed to salt stress by irrigation with 100 mM NaCl solutions. Salt stress significantly depressed G. mosseae-colonization but not P. occultum-colonization. Mycorrhizal association could markedly increase both plant performance (leaf number, leaf area, shoot, and root dry weights) and leaf relative water content of citrus seedlings exposed to salt stress. Root Na+ concentrations were lower in mycorrhizal than in non-mycorrhizal seedlings under given salinity conditions. Mycorrhizal inoculation was found to promote root concentrations of K+, Ca2+, and Mg2+ at all salinity levels, although the differences for Mg2+ was not significant at the 100 mM NaCl level. The K+/Na+, Ca2+/Na+, and Mg2+/Na+ ratios were higher in mycorrhizal than in non-mycorrhizal citrus roots subjected to salt stress. It seems that mycorrhizal inoculation possesses the potential to enhance salt tolerance of citrus.