Effects of low magnesium and an arbuscular mycorrhizal fungus on the growth, magnesium distribution and photosynthesis of two citrus cultivars

• The low soil Mg affected ‘Newhall’ seedlings growth more than ‘Ponkan’.
• AM improved the growth of ‘Newhall’ more than ‘Ponkan’ in low Mg soil.
• AM improved the Mg level of ‘Newhall’ more than ‘Ponkan’ seedlings in low Mg soil.
• AM improved the photosynthesis of ‘Newhall’ more than ‘Ponkan’ in low Mg soil.

The effects of the arbuscular mycorrhizal (AM) fungus, Glomus versiforme, on plant growth, magnesium (Mg) concentration and distribution, and photosynthesis in the ‘Newhall’ (Citrus sinensis Osbeck cv. Newhall) navel orange and ‘Ponkan’ (Citrus reticulate Blanco cv. Ponkan) tangerine grafted on the rootstock trifoliate orange (Poncirus trifoliata L. Raf.) were studied in potted cultures under Mg-poor and Mg-rich conditions. The low soil Mg inhibited the ‘Newhall’ seedlings growth more than that of ‘Ponkan’. This was accompanied by greater decreases of Mg concentrations and CO2 assimilation rate in the basal leaves, and lower soluble sugar concentrations in the roots of ‘Newhall’. AM inoculation improved the growth, the Mg concentrations in various plant parts, and the photosynthesis of the two cultivars, especially the ‘Newhall’ seedlings under the Mg-poor condition. These results suggest that G. versiforme has the potential to enhance growth and Mg distribution in ‘Newhall’ seedlings grown in low Mg soil in a greenhouse.