Investigation of the possibility of reducing the effects of low irrigation of lavender (Lavandula officinalis L.) using biofertilizers and phosphorus through changes in some morphological and biochemical characteristics

Lavender (Lavandula officinalis L.) belonging to the Lamiaceae family is a plant with economic, medicinal and ornamental value. Its essential oil is used as a raw material for many industries, including perfumery, cosmetics, and pharmaceutical industries. Drought stress as a limiting factor reduces growth and productivity in plants. This issue is especially important in arid and semi-arid regions of the world such as Iran. One of the basic solutions to adjust or reduce the effect of water stress in agricultural plants is the use of different types of biological fertilizers. Also, its low diffusion speed in the soil can play an important role in the lack of its ions in the solution in the soil of the root development area. In most agricultural systems, due to the low mobility of phosphorus in the soil, absorption by the plant is low. In order to investigate the effect of biofertilizers and phosphorus on reducing the effects of irrigation deficiency in lavender, an experiment was conducted in the form of split plots in a randomized complete block design with 3 replications at the Research Station of the Faculty of Agriculture, Islamic Azad University of Tabriz in 2019-2020.

Experimental factors including irrigation levels (irrigation after 60, 90 and 120 mm from Class A evaporation pan) as the main factor and inoculation with biofertilizer including four levels (inoculation with Thiobacillus, Pseudomonas and Thiobacillus + Pseudomonas and no inoculation As control) and phosphorus fertilizer levels at two levels (0 and 50 kg ha-1) as a secondary factor. The studied traits included leaf dry weight, flower dry weight, cell membrane leakage rate, relative leaf water content, soluble sugars and proline content, catalase and superoxide dismutase enzymes and peroxidase and MDA. To measure the activity of antioxidant enzymes, leaf samples kept at -80 degrees Celsius were used. The activity of catalase was measured using the method described by (Aebi, 1984; Ezhilmathi, 2007). The measurement of superoxide dismutase (SOD) enzyme was calculated according to the method (Giannopolitis and Ries, 1977) based on enzyme unit per milligram per body weight. The determination of malondialdehyde (MDA) was based on Aston and Sidney's method (Aston and Sidney, 1987). Proline content in the youngest leaf was also determined by the method of Bates et al. (1973). SAS version 8 software was used to analyze the variance of the data, MSTATC version 2 software was used to compare the averages, and Excel software was used to draw the figures.

The results showed that at all levels of irrigation, phosphorus consumption and inoculation with integrated biofertilizers increased the dry weight of flowers compared to the control. Irrigation after 60 mm of evaporation from the pan with the application of 50 kg of phosphorus per hectare and application of Thiobacillus + Pseudomonas obtained the highest dry weight of flowers (833.3 g ha-1). The highest leaf dry weight was proline, catalase, peroxidase, superoxide dismutase and malondialdehyde at 60 ml of evaporation with 50 kg ha-1  application and application of Thiobacillus + Pseudomonas. The results of this study also showed that the effects of interaction between irrigation, phosphorus and biofertilizer levels on cell membrane leakage, leaf dry weight and relative leaf water content were not significant.

Based on the results of this experiment, it can be said that in water stress conditions, the use of biological fertilizers combined with the use of phosphorus fertilizers can greatly reduce the incidence of malnutrition in lavender medicinal plant. The accumulation of soluble sugars, proline and the increase in the activity of antioxidant enzymes in this plant in the face of drought stress can be considered as drought tolerance mechanisms. The combined use of Thiobacillus and Pseudomonas bacteria had better results than the use of these bacteria alone; Therefore, if the intensity of water deficit stress in this plant is not high, the effects of water deficit stress can be reduced by using biological fertilizers and phosphorus fertilizer.