Soil Liming Ameliorates Crude Oil Stress and Promotes Biochemical Indices and Photosynthetic and Antioxidant Enzyme Activities in Lemongrass ( Cymbopogon citratus )

Crude oil contamination is a serious environmental threat to agricultural soils. Different methods have been employed to ameliorate crude oil-contaminated soils. However, little is known about the effects of liming on plants grown in crude oil-contaminated soils. In a glasshouse experiment, fresh soil was mixed with different amounts (0, 1.75, 3.5, 5.25, or 7.0 kg) of crude oil-contaminated soil equivalent to 0%, 25%, 50%, 75%, and 100% dry weight basis of the total soil.pot −1 (i.e., 7 kg soil.pot −1 ). To half of the contaminated soils, agricultural lime (aglime) was added as 3% of the amount of contaminated soil. Thereafter, lemongrass ( Cymbopogon citratus ) was grown in all the pots. After 45 days, growth, physiological, and biochemical properties of lemongrass were measured. Compared to plants without crude oil exposure, increasing amounts of crude oil in the soil significantly decreased all measured plant parameters (shoot and root lengths and dry weights, chlorophyll and carotenoid contents, total soluble proteins and amino acids, antioxidant enzyme activities, and secondary metabolites). However, compared to stressed plants without amendment, lime application increased lemongrass shoot and root lengths and biomass by about 20–50%, chlorophyll content by about 20–60%, carotenoid content by about 20–30%, total soluble proteins by about 15–30%, total free amino acids by about 10–40%, antioxidant enzyme activities by about 10–50%, and secondary metabolites by about 30–50%. Our findings suggest that soil liming could be a simple environmentally friendly method to ameliorate the deleterious effects of crude oil contamination on plants.