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Polycyclic aromatic hydrocarbons (PAHs), a class of organic pollutants, have been observed to exert deleterious effects on plant growth and various physiological processes. In this study, the effect of different concentrations of phenanthrene (0, 25, 50, 75, and 100 ppm) on growth parameters, photosynthetic pigments, some antioxidant enzymes, and some biochemical compounds of the maize plant were investigated. The experiments were conducted as pot cultures of plants under controlled conditions using a completely randomized design (CRD) with three replications for each treatment. Increasing phenanthrene concentration reduced all studied growth parameters and significantly increased photosynthetic pigment contents. Phenanthrene led to the increase in catalase, peroxidase, and superoxide dismutase activities in the roots but in shoots, only the peroxidase activity was increased. Moreover, higher phenanthrene concentrations were associated with elevated levels of malondialdehyde and hydrogen peroxide, coupled with a marked reduction in soluble sugar content in both shoot and root tissues (p<0.05). Also, increase in phenanthrene concentration in the shoots decreased the total phenol and flavonoid contents compared to anthocyanin. Phenanthrene treatment led to a significant reduction in the concentrations of lauric acid, meric acid, palmitic acid, and oleic acid in maize shoots. In conclusion, it seems that high concentrations of phenanthrene induce oxidative stress in the maize, and plants improve their enzymatic antioxidant system to moderate the stress condition. In addition, damage of cell membranes by phenanthrene leads to weakening of plants root system as well as disordering in water and nutrient uptake and finally reduction in the plant growth.
 

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In most semiarid and arid areas, fresh water shortage compels managers to use low quality water sources with high salinity to irrigate turf and landscape. Recent research has noticed that management of nitrogen fertilization can alleviate salinity effects on plants. This greenhouse sand culture experiment was conducted in order to investigate morphological and physiological responses to salinity stress in Kentucky bluegrass (Poa pratensis L.) grown using different nitrogen sources. Three salinity levels (0, 40 and 80 mM NaCl) and three NO₃^-/NH₄⁺ ratios (6/0.5, 6/1 and 6/2) were applied in nutrient solutions. Under non saline conditions, higher ammonium concentration increased Turf Quality (TQ), leaf NO₃^-, proline content, Nitrate Reductase Activity (NRA), shoot and root growth. On the other hand, leaf potassium (K⁺) sodium (Na⁺) and MalonDiAldehyde (MDA) content were not affected. During the first week, the 40 mM NaCl treatment showed that the positive effects of NH₄⁺ on salinity tolerance were still perceptible. However, the 80 mM NaCl treatment showed that the adverse effects of high salinities were more pronounced when turf received high ammonium rate nutrient solution, as manifested by the decrease of TQ, NO₃^-, NRA, K⁺/Na⁺ ratio, shoot and root growth and by the increase of leaf MDA content. This suggests that effects of NO₃^-/NH₄⁺ ratio on salt tolerance varies with salinity levels.