Seedling Emergence and Biomass Growth of Oleaginous and Other Tropical Species in Oil Contaminated Soil

ABSTRACT

Germination rate in contaminated soils cannot be used as the sole indicator to select suitable species for phytoremediation trials, since it does not predict the plant development after germination. As a result, most screening tests for selection of specie with phytoremediation potential to treat contaminated soils include germination rate and biomass production. These screenings take several months and considerable space in greenhouses. As an attempt to reduce the time required for screening, seedling emergence and root and aerial biomass growth in a very early stage of plant development were investigated in soil contaminated with crude oil. The experimental design was based on a factorial of 6x6x50 where seeds from six tropical species (Ricinus communis - castor bean; Helianthum annus - sunflower, Glycine max - soybean; Acacia holosericea - candelabra wattle; Brachiaria brizantha – braquiaria; Tibouchina granulosa - quaresmeira) were placed in sterilized sand contaminated with crude oil at 6 oil concentrations (0% - control, 0.05%, 0.5%, 2%, 4% and 6% weight/dry weight) in boxes with 50 seeds. Four replicates resulted in a total of 7200 seeds (1 200/specie) in 144 experimental units kept in a greenhouse under light and temperature controlled conditions. It was observed that depending on the oil concentration and specie, germination can be significantly (α = 0.05) postponed or reduced and root as well as aerial dry biomass can be reduced. Root biomass increase was observed for oleaginous species soybean, sunflower and castor bean. Candelabra wattle was the only specie not significantly affected. The results support the hypothesis that more than one type of oil-soil-plant interaction might occur. The ranking in terms of tolerance to the crude oil, considering all variables analyzed was: A. holosericea > G. max = B. brizantha > H. annus > R. communis > T. granulosa. The low cost and short time required by the screening procedure proposed make it useful and effective for testing many species simultaneously, as the first step of a full-scale phytoremediation trial.