Effect of Climatic Factors on Essential Oil Accumulation in Two Lamiaceae Species from Algerian Semiarid Lands

Abstract

Plant metabolism is vastly influenced by climatic factors in terms of quantity and quality. In this regard, the objective of this study was to assess the impact of some climatic factors on the amount of essential oils (EOs) in two plant species growing spontaneously in an Algerian semiarid zone: Thymus algeriensis Boiss & Reut. and Rosmarinus officinalis L. for five successive years (2010–2014). Essential oils were extracted from plant aerial parts by hydrodistillation using Clevenger type system and the oil yield rates were estimated in relation to the dry matter of the plants. The obtained results showed significant differences in EO yields during the five years, among the species and the interaction ‘Year × Species’ (P < 0.001). R. officinalis accumulated the best oil content during 2010, 2012 and 2013 with 1, 0.93 and 0.88% respectively. T. algeriensis yielded higher EOs in 2013 followed by 2012 and 2011 with 1.08, 0.67 and 0.59% respectively. Furthermore, R. officinalis produced higher EO amount than T. algeriensis. Oils accumulation increased significantly with the increase of precipitation, wind speed and hygrometry but was negatively influenced by air humidity and aridity in both species.

Appendix 1

Results from the generalized linear model (Gaussian GLM) testing the effects of climate factors on the variation of essential oil concentrations in Rosmarinus officinalis and Thymus algeriensis growing in semiarid regions of Algeria.

GLM coefficient summary
Variables	Estimate	SE	t-value	P	Sig.
Intercept	4.209	2.363	1.781	0.089	ns
Thymus algeriensis	−0.627	0.180	−3.481	0.002	**
Mean temperature	0.025	0.093	0.265	0.793	ns
Precipitation	0.010	0.003	3.447	0.002	**
Air humidity	−0.080	0.023	−3.511	0.002	**
Wind speed	0.081	0.034	2.416	0.024	*
Hygrometry	0.400	0.106	3.758	0.001	**
De Martonne aridity	−0.084	0.022	−3.764	0.001	**
Type III F-test
Variables	Df	SS	F	P	Sig.
Plant species	1	0.121	12.117	0.002	**
Mean temperature	1	0.001	0.070	0.793	ns
Precipitation	1	0.118	11.882	0.002	**
Air humidity	1	0.123	12.328	0.002	**
Wind speed	1	0.058	5.837	0.024	*
Hygrometry	1	0.141	14.124	0.001	**
De Martonne aridity	1	0.141	14.168	0.001	**
Residuals	22	0.219

1. SE: standard error, P: probability value, Df: degrees of freedom, SS: sum squares, F: F-statistics, Sig.: significance codes.
2. ^**: P < 0.01, ^*: P ≤ 0.05, ^ns: P > 0.05.