Arbuscular Mycorrhizas and Phosphorus Fertilizer Affect Photosynthetic Capacity and Antioxidant Enzyme Activity in Peppermint Under Different Water Conditions

Abstract

In order to investigate the effect of arbuscular mycorrhizas and phosphorus levels on photosynthetic capacity and enzyme activity in peppermint under different water conditions, an experiment was conducted during the 2017–2018 growing seasons. The experimental treatments comprised water deficiency at three levels (a1: irrigation after 70 mm evaporation from pan of Class A, a2: irrigation after 110 mm evaporation from pan of Class A, and a3: irrigation after 150 mm evaporation from pan of Class A), phosphorus fertilizer at three levels (without phosphorus fertilization, 25% recommended phosphorus amount, and 50% recommended phosphorus amount), and different mycorrhiza species (nonmycorrhizal inoculation, <em>Rhizophagus intraradices</em>, <em>Funneliformis mosseae</em>, <em>Glomus hoi</em>, and mixture of all three species). Results showed that water stress significantly reduced chlorophyll <em>a</em>, chlorophyll <em>b</em>, total chlorophyll, and essential oil yield, but increased the stomatal resistance of peppermint. The essential oil yield of peppermint was significantly reduced by severe water deficit (a3). However, inoculation with <em>R. intraradices</em>, <em>G. hoi</em>, and a mixture of all three species under severe water deficit, increased the essential oil percentage of peppermint by 21%, 21%, and 31.5%, respectively. Application of 50% recommended phosphorus fertilizer increased the yield of essential oil by 18.9%. In addition, menthol increased by 24.1% (highest) under a3 irrigation, using 25% of the optimal dosage of phosphate fertilizer and nonmycorrhizal inoculation. The maximum catalase and peroxidase activity was obtained in the treatment of <em>G. hoi </em>mycorrhizal fertilizer, after application of 25% recommended dose of phosphorus fertilizer and a2 and a3 irrigation.