RESUMEN
The aims of this study were to (1) establish the intrapopulation and seasonal variation of Juniperus excelsа essential oil (EO); (2) compare the J. excelsa concrete and resinoid composition with its EO composition; and (3) investigate the potential herbicidal activity of J. excelsa EO against seeds of Papaver rhoeas L., Consolida orientalis (J.Gay) Schrödinger, Anthemis arvensis L., Avena fatua L., and Agrostemma githago L. Four independent studies were performed to meet these objectives. Twenty-eight individual trees were analyzed from two populations to establish intrapopulation and interpopulation variability of EOs yield and composition. In the seasonal dynamic study of leaf EO, samples from the same three trees and in the same population were collected in January, March, May, July, October, and December and their EO yield and composition determined. The EOs (intrapopulation and seasonal) were extracted by hydrodistillation, while the EO for the herbicidal test was obtained by steam distillation in a semi-commercial (SCom) apparatus. Overall, the EO yield varied significantly from 0.93% to 2.57%. α-Pinene (8.85-35.94%), limonene (11.81-50.08%), and cedrol (3.41-34.29%) were the predominant EO compounds in all samples (intrapopulation variability); however, trans-2,4-decadienol and ß-caryophyllene were predominant in some individual trees. Four chemical groups were identified in the samples collected from two natural populations (intrapopulation). This is the first report on the compositions of J. excelsa concrete and resinoid. Cedrol (15.39%), 7-hydroxy-4-methyl-coumarin (17.63%), 1-octacosanol (36.85%), tritriacontane (16.08%), and tiacontanoic acid were the main compounds in the concrete and resinoid. Juniperus excelsa EO suppressed seed germination and seedling growth of P. rhoeas, C. orientalis, A. arvensis, A. fatua, and A. githago, demonstrating its potential to be used for the development of new biopesticides. The highest EO yield with high content of limonene and cedrol was obtained from samples harvested during the winter months (December, January, and March).
