Effects of Bio-Fertilizers and Different Levels of Phosphorus on Biochemical Traits, Essential Oils, and Antioxidant Enzymes in Lavender (Lavandula Angustifolia) Under Water Stress

Abstract To investigate the effects of biological fertilizers and phosphorus on the effects of reduced irrigation in medicinal plant lavender, a split-split plot experiment based on randomized complete block design (RCBD) with three replications was conducted during two cropping years of 2018/2019 and 2019/2020 at The Research Station, Islamic Azad University of Tabriz. The studied treatments in this research included irrigation levels (irrigation after 60, 90, and 120 mm of class A evaporation pan) as the main factor, four levels of seed inoculations (inoculation with Thiobacillus, inoculation with Pseudomonas, combined inoculation (Thiobacillus + Pseudomonas) and control (non-inoculation) as a sub-factor and the amount of phosphorus chemical fertilizer (0 and 50 kg/ha) was as a sub-sub-factor. The experiment assessed several traits, including dry weights of flowers, the quantity of cell membrane leakage, leaf relative water content, soluble sugars content, proline content, superoxide dismutase, catalase, and peroxidase activities. This two-year experiment measured the following traits: Wet weight of the flower, quantity of cell membrane leakage, leaf relative water content, proline, superoxide dismutase, catalase, and peroxidase activities. The wet weight of flowers increased compared to the control during the first year of the investigation due to all irrigation levels, phosphorus application, and inoculation with integrated biological fertilizers. Results showed that in the first year of measuring, all irrigation levels, phosphorus application, and integrated biological fertilizer inoculation increased the wet weight of the flower compared to the control. The greatest amount of proline, catalase, peroxidase, and superoxide dismutase enzymes was obtained at 60 ml of evaporation with a consumption of 50 kg of phosphorus per hectare and applying Thiobacillus + Pseudomonas. This study also showed that the interactions between irrigation levels, phosphorus fertilizer, and biological fertilizer on the characteristics of cell membrane leakage rate and leaf-relative water content were not significant. The results of the second-year experiment showed that the highest amount of catalase, superoxide dismutase, and peroxidase was obtained as a result of the irrigation combination after 120 mm of evaporation pan and the application of Thiobacillus + Pseudomonas and phosphorus fertilizers and proline content (5.48 mg/g wet weight) were determined by irrigation treatment after evaporation of 120 mm and without application of bacteria and phosphorus fertilizers. It appears that plant growth-promoting bacteria and phosphorus increased the yield of lavender flowers by reducing the negative effects of drought stress.