Organic matter decay in coastal wetlands: an inhibitory role for essential oil from Melaleuca alternifolia leaves?

Abstract

Essential oils are a common component of the leaves of many plants, and may be a factor that, to date, has been overlooked as a determinant of leaf decay in natural environments. Cellulose sheets and dried leaves of Platanus sp. (common plane tree) treated with essential oil extracted from Melaleuca alternifolia CHEEL and buried in soil in laboratory mesocosms decayed at a significantly slower rate than did control materials not treated with the oil. Inhibition of bacterial activity may account in part for this effect on organic matter decay, since Melaleuca essential oil at concentrations of greater than 0.001% v/v markedly inhibited the growth of the bacterium, Escherichia coli. Melaleuca essential oil was lethal to starved bacteria (E. coli, Staphylococcus aureus and Pseudomonas aeruginosa), especially at higher concentrations (>0.I % v/v) of the oil. EC 50 values, determined with the Microtox assay, were c. 0.01 % v/v, a value equivalent to an essential oil concentration of about 100mg/l. Essential oil derived from Melaleuca leaves and twigs may have a significant role in organic matter processing and nutrient cycling in coastal wetlands by slowing the decomposition of organic detritus and inhibiting or killing microbes.