Effect of chemical and biological fertilizers on the physiological characteristics and activity of some antioxidant enzymes of peppermint (Mentha piperita) under drought stress conditions

In order to evaluate the effect of various irrigation regimes and different fertilizer combinations on some morphological and physiological traits of Mentha piperita, a greenhouse experiment was carried out at the research greenhouse of Ferdowsi University of Mashhad, during growing season 2017-2018. The experiment was conducted in factorial experiment based on completely randomized design with three replicates. Factors were consisted of different irrigation regimes levels: 100% FC, 75% FC and 50% FC, and different biological and chemical fertilizers combinations including:1-biochemical bacterial NPK + NPP, 2- NPP bio-fertilizer, 3-NPK, 4-micronutrient fertilizer (MIC), 5-MIC + amino acid fertilizer (AP). The results showed that interaction of irrigation regimes and different biofertilizers on Proline had different significant at 5% level. The highest proline amount (0.22 mg /g fresh weight) were obtained in irrigation of 100% FC and NPK + NPP combination fertilizer treatments. Also, the results of variance analysis showed that the main effects of irrigation regimes and fertilizer types on chlorophyll a, chlorophyll b, carotenoid, total chlorophyll, ascorbate enzyme, catalase, peroxidase and essential oil percentage were significant. The results show that biofertilizers application decreased the antioxidant enzymes activity compared to other chemical fertilizers, slowly supply of nitrogen and phosphorus through the use of bio fertilizers during plant growth, likely this could reduce the intensity of stress in plants by providing the balanced plant nutrient and enough energy to grow and survive the plant and the antioxidant enzymes activity has also decreased due to the decrease in stress.