Root and Shoot Biomass of Plants Seeded in Crude Oil Contaminated Soil

Abstract

Using plants to enhance remediation of soil contaminated with crude oil is a viable remediation strategy. Rapid vegetative growth forms a plant canopy that acts to contain the contaminated soil by reducing surface runoff and erosion. Root growth in these soils stimulates microbial activity in the rhizosphere, which may accelerate bioremediation by measuring root and shoot biomass. In a greenhouse experiment, seeds were sown into a Windthorst sandy clay loam soil contaminated with 0 (control), 0.5, 5, or 10% unweathered North Central Texas crude oil. Experimental units consisted of seed flats with dimensions of 55 x 28 x 3.2 cm (L x W x H) with 20 individual rows. Seeds were sown in separate rows at the rate of 10 seeds per row. Soil moisture was maintained near-30 kPa pressure by using subsurface irrigation. Treatments were conducted in triplicate in a completely randomized design. Plants were grown for 28 days after seeding. On day 28, root and shoot biomass was measured and the presence of nodules was noted. Averaged across all nineteen species, soil crude oil concentration of 0.5, 5, and 10% decreased shoot biomass by 75.8, 96.7, and 99.3% and root biomass decreased by 72.1, 96.1, and 99.5% relative to the control treatments. Lablab (Lablab purpureus) had the greatest shoot and root biomass production in the treatment with 0.5% crude oil. In the treatment with 5% crude oil Kenaf #2 (Hisbiscus cannabinus var. tainvng #2) had the greatest shoot and root production and in the 10% crude oil treatment Kenaf #3 (Hisbiscus cannabinus var. sf 459) had the greatest shoot and root production. The presence of unweathered crude oil inhibited nodule formation on all legumes. Results indicate that the species with the greatest potential to enhance phytoremediation are Lablab for soil with approximately 0.5% crude oil, Kenaf #2 for soil contaminated with approximately 5% crude oil and Kenaf #3 for soils contaminated with 10% crude oil. Due to the drastic reduction in shoot and root biomass in crude oil contaminated soil, over-seeding, transplanting healthy plants, and delaying seeding to allow time for volatile phytotoxic-compounds to volatilize may decrease the time for a plant canopy establishment, encourage greater root biomass, and enhance phytoremediation.