The scope of this study was to examine the degradation process of Mentha spicata leaves and essential oil in the soil environment. Spearmint leaves were used for
soil amendment at different concentrations (2, 4 and 8g leaf d.w. 100g-1 soil). The decomposition process and essential oil features were examined after a
period of 15, 35 and 60 days; following soil hydro-distillation, essential oil constituents
were analysed by GC-MS. The soil content in spearmint essential oil was reduced by
more than 90% during the two-month experimental period. The oil composition was also
dramatically altered. From the monoterpenoids, 8 were absent in the last sampling
and the rest were found in much lower concentrations; carvone, which was the main
oil constituent making about 50% of the oil, was reduced to only 1% in all treatments,
60 days after addition of the leaves into the soil. In contrast, all sesquiterenoids
were persistently detected in all treatments and all samplings; their relative contribution
increased at the expense of monoterpenoids. Most pronounced increase was recorded
for caryophyllene and bourbonene. These results indicating a rapid degradation of
monoterpenoids are in accordance with previous reports [1]. Additionally, the persistence
of sesquiterpenoids in the soil environment could explain findings regarding use of
these compounds in root signaling, as is the case of caryophyllene release by maize
roots upon insect damage [2], or the increase of sesquiterpenoids in rice seedlings
after methyl jasmonate treatment [3].
Acknowledgements: Research was funded by the General Secretariat of Research and Technology,
Ministry of Development, Greece (O1 ED 317)
References: 1. Vokou, D. et al. (2006) Microorganisms and allelopathy: a one-sided
approach in Allelopathy: A Physiological Process with Ecological Implications (Reigosa, M.J.,
Pedrol, N., Gonzalez, L., eds), Springer, Dordrecht, 341–371.
2. Rasmann et al. (2005) Nature 434:732–737.
3. Cheng et al. (2007) Phytochemistry 68:1632–1641
