Altitude and climate influence Helichrysum italicum subsp. microphyllum essential oils composition

Helichrysum italicum (Asteraceae) is a small shrub of the Mediterranean area which colonizes a wide range of habitats. In Sardinia, Italy, the species is widely dispersed in different environments ranging from sandy beaches to holm hoak forests 1250. m above sea level (a. s. l.). Recently, the species has been attributed an increasing economical value mainly for its pharmacological, aromatic proprieties and ornamental uses. In this study, the chemical profiles of 146 H. italicum ssp. microphyllum genotypes from two contrasting habitats (seaside and mountains) in Sardinia were explored. Significant differences in volatile fractions between the two groups were found, displaying a correlation between secondary metabolite production and habitat type. Multivariate analysis of variance revealed that monoterpenes, sesquiterpenes (oxygenated/not oxygenated), alcohols, ester were quantitatively differentially produced in the plants growing under different environmental conditions ( P<. 0.0001). However, discriminant analysis also showed that compositional separation among samples is not simply the question if the habitat is from the coast or the mountains: plants from four seaside sites separate most remarkably from the rest, and in the latter plants from three mountain sites become distinct. It means that there is a fairly homogeneous and large group of plants in which habitat type is not a distinguishing feature regarding volatile oil composition.Considering the importance of climatic conditions in plant development and growth, the relationship between meteorological variables and chemical compounds of the volatile fraction was explored by principal component analysis. Nerolidol is mostly positively correlated to mean winter temperature, while italicene, bergamotene, nerol and curcumene are positively influenced by spring and summer precipitation. Finally, Mantel test revealed a significant correlation (Spearman, P= 0.002) between chemical and meteorological matrices of Euclidean distances, suggesting that the most diverse chemical profiles belonged to plants from the farther climatic locations.