Plant growth and essential oil content of Mentha crispa inoculated with arbuscular mycorrhizal fungi under different levels of phosphorus

The occurrence of mycorrhizal association with plant roots causes an increased absorption of water and improves soil nutrient uptake, mainly phosphorus (P), what also affects the plant metabolism. This work aimed to study the growth of plants of Mentha crispa L. and their essential oil (EO) content, cultivated with and without arbuscular mycorrhizal fungi (AMF) inoculation of Glomus etunicatum and Rhizophagus clarus under different levels of P. The treatments tested were 21mgPdm−3 soil (low level) and 200mgPdm−3 soil (high level) added to the initial soil inoculated or not with two AMF species at the beginning of the experiment in pots filled with 3.5kg of fumigated soil for each pots. The experiment was performed in greenhouse using a completely randomized design in a 2×2 factorial: 2 levels of P (Low and high) and AMF inoculation (with and without) with six repetitions. The density of spores and AMF root colonization, the plant fresh matter, and the content and composition of the EO of M. crispa were determined four months after transplantation. The density of AMF spores was not significantly affected by the P addition; however, the AMF root colonization decreased significantly when P was applied to the soil. The plant inoculated with G. etunicatum presented the highest root colonization (61%) at low P in the soil. The plants inoculated with R. clarus presented the highest production of fresh matter, shoot height and number of leaves when P was applied to the soil. The plants inoculated with G. etunicatum showed the highest EO content (0.98%) at low P in the soil. However, when P was applied to the soil, the EO content reduced to 0.09%. The EO chemical composition was not drastically affected by the treatments and 10 components were found, the main ones being limonene (3–19% of total EO composition) and carvone (72–86% of total EO composition).