Electrical conductivity of nutrient solutions affects the growth, nutrient levels, and content and composition of essential oils of Acmella oleracea (L.) R. K. Jansen from southeastern Brazil

Jambu, a plant native to the Amazon, is rich in essential oils, particularly spilanthols and phytols. Although hydroponic cultivation of this vegetable is practiced, the process remains relatively understudied. In this context, this study aimed to assess the influence of electrical conductivity of nutrient solutions on jambu production. Greenhouse experiments were conducted at Universidade Estadual do Norte Fluminense (UENF), Brazil, employing a randomized block design encompassing six blocks comprising six Hoagland and Arnon nutrient solutions with electrical conductivities of 0.5, 1.0, 2.0, 2.5, 3.0, and 4.0 mS cm-1. Harvesting occurred 72 d after sowing, and the plants exhibited improved growth at electrical conductivity close to 3.5 mS cm-1. The levels of N, P, K, B, Zn, Mn, and essential oils of jambu plants increased linearly with increasing electrical conductivity. Twenty-three compounds were detected among the investigated essential oils, with spilanthol, phytol, and acmellonate present in the highest amounts. Increase in electrical conductivity led to increases in the percentage areas of several compounds, such as (Z,Z)-1,8,11-heptadecatriene, caryophyllene, 6-pentadecen-1-ol, 1-pentadecene, spilanthol isomer 1, (E)-beta-ionone, kessane, and caryophyllene oxide. Furthermore, higher electrical conductivity resulted in decreasing percentages of compounds such as spilanthol, phytol, and Compound 2. Notably, a 609.74 % increase in caryophyllene and a 25.65 % reduction in spilanthol were observed with increasing electrical conductivity. These results suggest that the productivity of jambu plants is improved, including the production of essential oils, with cultivation in solutions with electrical conductivities above 2.5 mS cm-1. However, this condition may negatively affect most cultivated vegetables. The mechanisms underlying the increased tolerance of jambu to higher electrical conductivities require further investigation.