Light-regime-dependent modulation of biomass allocation and oxygenated sesquiterpene balance in vetiver root essential oil

Light is increasingly used as a management tool in controlled cultivation of aromatic plants, but its effects on root-derived, sesquiterpene-rich essential oils remain poorly defined. Rooted slips of Chrysopogon zizanioides were cultivated for 13 months under natural greenhouse daylight, Red-Blue LED, or White LED. Growth traits, root biomass, and essential oil (EO) content were evaluated, and EO composition was characterized by GC–FID and GC–MS. Plants grown under White LED showed the greatest shoot elongation, whereas Red-Blue LED favored root elongation without a corresponding increase in root dry biomass. Control plants under natural daylight produced the greatest root biomass and numerically highest EO content (0.88%), although EO content did not differ significantly among treatments. The oil remained dominated by oxygenated sesquiterpenes under all light regimes. Red-blue LED increased the relative contribution of khusimol and khusiol while decreasing α- and β-vetivone. Dry-root-mass-based semi-quantitative estimates indicated that the higher relative abundance of khusimol did not correspond to greater estimated accumulation, whereas lower estimated contents of α- and β-vetivone remained evident. Exploratory CLR-PCA was consistent with this compositional contrast, and the selected alcohol-to-ketone ratio was highest under Red-Blue LED. Overall, the results indicate that light regime was associated more strongly with changes in the relative balance of selected oxygenated sesquiterpenes than with enhancement of EO content.