The effect of organic and chemical nitrogen fertilizer application on chlorophyll fluorescence indices, chlorophyll and flavonoid content, photosynthesis rate, leaf area index and dry matter yield of peppermint under deficit water stress

In order to determine the effects of water deficit stress, nitrogen fertilization on chlorophyll fluorescence, chlorophyll and flavonoid content and LAI dry matter yield of Peppermint, a split plot experiment was laid out in a randomized complete block design with three replications in the research field of Tarbiat Modares University in 2018. The experimental treatments consisted of three irrigation regimes (respectively after depleting 25, 40 and 55% of available water in the root growth zone) as the main factor and six fertilizer treatments based on nitrogen requirement as sub-factors. The results demonstrated that water deficit stress significantly decreased maximum chlorophyll fluorescence (Fm), variable chlorophyll fluorescence (Fv), the photochemical efficiency of PSII (Fv/Fm), photosynthesis rate, LAI and dry matter yield, but minimum fluorescence (F0) and flavonoid concentration increased under water deficit stress. The results indicate that the drought stress caused the light inhibition of photosystem II and also, by reducing the leaf area, led to a decrease in the yield of dry matter of peppermint in such a way that the severe drought stress caused a decrease of 43% compared to the control. On the other hand, in most of the examined traits, the treatments that were treated with nitrogen fertilizer (especially vermicompost) improved the photosynthetic indices and, finally, the dry matter performance of the plant and also managed to moderate the negative effects of severe water deficit stress on them. In addition, in the direction of sustainable agriculture and due to the medicinal nature of peppermint, it is possible to reduce the consumption of chemical fertilizers by 50% by combining urea and vermicompost.