Salicylic Acid Mitigates Toxicity of Polycyclic Aromatic Hydrocarbons to Pennisetum purpureum cv. Mahasarakham Grown in Sandy Soil

Sweet grass (Pennisetum purpureum cv. Mahasarakham) is an interesting plant for phytoremediation in low-quality soils. This plant could improve the removal of many pollutants, including polycyclic aromatic hydrocarbons (PAHs). The salicylic acid application is expected to enhance PAH plant tolerance and phytoremediation ability. Before planting in non-contaminated or 100 mg/kg anthracene +100 mg/kg pyrene-contaminated soils, sweet grass cuttings were treated with 100 mg/L salicylic acid using two methods: 1) immersing for 24 h before planting or 2) immersing for 24 h before planting followed by watering on day 0. After 30 days, the measurements, included shoot growth, root growth, remaining PAHs in soil, pigment levels, proline, and relative water content, were taken. The results showed that salicylic acid could enhance shoot and root growth, along with the chlorophyll and carotenoid contents in the leaves of sweet grass growing in PAH-contaminated soils. Additionally, salicylic acid decreased the proline content in the leaves but did not affect the relative water content. These results showed that salicylic acid could enhance sweet grass tolerance to anthracene and pyrene. This was consistent with the role of salicylic acid in environmental stress elimination in plants. This was possible to relate the PAH removal enhancement from soil. The most effective method for stimulating sweet grass growth in PAH-contaminated soil was immersing for 24 h before planting.