Effects of mycorrhizal colonization and fertilization on growth and photosynthesis of sweet basil under salt stress

A greenhouse experiment was conducted to investigate the effects of inoculation with an arbuscular mycorrhizal fungus (AMF) and of different levels of fertilization on growth, photosynthetic efficiency, and ion uptake by sweet basil (Ocimum basilicum L.) in conditions of saline stress. Eight different treatments were compared, deriving from the factorial combination of two levels of fertilization, two levels of salinity of the irrigation water and the presence or absence of mycorrhizal colonization, performed with a crude inoculum of Glomus intraradices Schenck and Smith. Salinity significantly reduced growth and fluorescence level of plants, and higher sodium (Na) and chloride (Cl) contents in both roots and shoots were associated with these phenomena, while potassium (K) was slightly reduced. Both mycorrhizal inoculation and high fertilization acted in the direction of reducing the symptoms of salinity stress by increasing growth and fluorescence. Mycorrhizal colonization showed generally more pronounced effects than a high application rate of fertilizer. The simultaneous application of colonization and high fertilization provided higher tolerance to salinity than one single factor, but the combined effect was less than proportional to the sum of the separate effects. In particular, the differences in growth and photochemical efficiency between inoculated and uninoculated plants under salt stress were significantly reduced by the contemporary presence of additional fertilization. The rate of root colonization by the mycorrhizal fungus was significantly reduced by both saline irrigation and high fertilization.