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ŠUMARSKI LIST 5-6/2012 str. 49     <-- 49 -->        PDF

Results and discussion
Rezultati i rasprava
Growth of plants – Rast biljaka
Plant growth and establishment at contaminated sites provide useful information defining the species tolerance and phytoremediation potential. Contamination of the environment with crude oil may affect plant performance by creating conditions which make essential nutrients like nitrogen and oxygen needed for plant growth unavailable (Ogbo et al., 2009). To cope with and survive such conditions, plants should enhance the degradation of petroleum hydrocarbons in soil by stimulation of growth and activity of microorganisms capable for degradation of petroleum hydrocarbons in the rhizosphere (Frick et al., 1999; Merkl et al., 2004). One of the most common symptoms of the pollutant phytotoxicity is reduction of plant growth. In the present work, crude oil contamination considerably affected growth of pop­­lars (Fig.1 and Fig.2). Shoot and root fresh mass of clo­nes ´9111/93´ and ´Pannonia´ substantially decreased along with increase of the contamination level. However, low levels of crude oil (5 %) stimulated shoot growth in clone ´Bora´, while root growth was not changed in plants exposed to 5 and 25 % treatment.
Growth reduction is caused by crude oil compounds (aliphatic, aromatic, naphthalic and phenolic like compounds), that may reduce dark respiration, transpiration and photosynthesis of leaves (Trapp et al., 2001). Plant growth on soils contaminated with crude oil affect both physical and chemical soil characteristics, leading to decrease of crude oil phytotoxicity, and these changes may be favourable for plant growth. Njoku et al. (2009) reported that Glycine max cultivated on crude oil contaminated soils did not significantly affect the crude oil level in some treatments, but improved physico-chemistry of the soil (pH, moisture, organic matter), which are coherent with plant growth. Previous investigations elucidated that plants may not reduce the concentration of contaminants but can reduce their toxicity (Sici­liano and Germida, 1998). However, changes in soil pH may contribute to activity of microorganisms capable for degradation of crude oil (Njoku et al., 2009). Higher degradation of petroleum hydrocarbon in vegetated than in non-vegetated soil was reported by Merkl et al. (2005b). In the present stu­dy, a clone specific growth under crude oil contamination may be the consequence of different tolerance of the genotypes to such conditions, and their differential ability to adopt changes in soil characteristics. Trapp et al. (2001) found Populus nigra to be more sensitive to diesel fuel than willows, Salix viminalis and S. alba. Preserved growth at