Germination, growth and physiological responses of mangrove plant (Bruguiera gymnorrhiza) to lubricating oil pollution

The effect of lubricating oil on germination, early growth and physiological responses of Bruguiera gymnorrhiza (L.), a common mangrove plant species in Hong Kong was investigated. Both fresh and spent (or used) lubricating oil at a single initial dose of 5 L m−2 did not have any effect on germination (i.e. initial establishment). All the oil-treated propagules were successfully developed into new seedlings within 30 days, same as the control (without any oil addition). This viviparous species had long slender propagules with an average size of 15 cm long, and only 1/3 of the exposed section of the propagule was covered by oil. On the contrary, germination of Aegiceras corniculatum (L.) Blanco and Acanthus ilicifolius L. in sandy as well as muddy mangrove sediments was totally inhibited by fresh and spent lubricating oil at the same dose, probably because their propagules were relatively small in size and were completely covered by oil. Although germination of B. gymnorrhiza was not affected, early growth including height, leaf number and biomass of the oil-treated seedlings was significantly reduced while the content of free radicals and malondialdehyde (MDA), and the activity of superoxide dismutase (an anti-oxidant enzyme) increased with oil treatment. These results indicate that lubricating oil, in particular spent oil, posed oxidation stress and caused lipid membrane damages leading to growth reduction in young seedlings of B. gymnorrhiza, and this impact was more significant in plants grown in sandy than in muddy mangrove sediments.