Simulated acid rain (SAR) induced alterations in plant morpho-physiology, leaf ultrastructure, cell viability, and yield - A case study on Mentha arvensis L. (Wild mint).

Acid rain (AR), a secondary pollutant, a product of sulfur and nitrogen oxides fusion with the atmosphere's water vapor, comes on earth in the form of rain, poses a significant environmental threat, and affects soil characteristics and plant morphology, ultrastructure, physiology, and yield. However, its effects on aromatic and medicinal plants remain insufficiently studied. Due to their low side effects and high efficacy, the use of herbal plants for disease remedy preparation is found globally and their consumption increases year after year. Mentha arvensis is such an aromatic crop, having great economic importance due to the essential oil present in its leaf. This research examines the influence of simulated acid rain (SAR) at varying pH levels (6.0, 5.0, 4.0, and 3.0) on morphology, growth, physiology, and yield parameters in M. arvensis. Results revealed that different concentrations of SAR exposure significantly (p ≤ 0.05) reduced growth and yield parameters, photosynthetic pigments and protein content, essential mineral composition, and phytochemical levels. Conversely, antioxidants activity such as catalase (CAT), superoxide dismutase (SOD), peroxidase (POX), ascorbate peroxidase (APX), lipid peroxidation marker malondialdehyde (MDA), osmo-protectant proline content, hydrogen peroxide (HO) content, superoxide ions content (O), and electrolyte leakage percent (EL) level increased significantly (p ≤ 0.05) as acidity intensified, particularly at pH 3.0. At pH 3.0, there was a notable reduction (p ≤ 0.05) in shoot length (55.63%), root length (55.42%), fresh weight (59.81% for shoots, 52.32% for roots), dry weight (62.88% for shoots, 55.56% for roots), number of leaves (56.13%), leaf area (60.53%), nitrate reductase (NR) activity (58.48%) and chlorophyll content (43.58% for chlorophyll 'a', 57.07% for chlorophyll 'b'). Phytochemicals such as menthol (12.08%), menthone Title page (40.07%), and menthyl acetate (33.63%) were significantly reduced while antioxidants activity such as CAT (144.71%), POX (260.37%), SOD (255.15%), APX (213.51%), MDA content (193.97%), proline content (607.18%), HO content (163.69%), O content (185.82%), EL percentage (57.23%) significantly (p ≤ 0.05) increased. The highest acidity level (pH 3.0) resulted in the most significant reduction in growth, yield, and the production of economically important phytochemical constituents, highlighting the harmful effects of simulated acid rain on the growth, productivity, biochemical characteristics, and commercial value of M. arvensis.