Water Stress Effects on Biomass Allocation and Secondary Metabolism in CBD-Dominant Cannabis sativa L.

Water availability is a key factor affecting both morphological development and secondary metabolite production in Cannabis sativa L. This study evaluated the effects of water stress applied during the vegetative and flowering stages on plant performance, cannabinoid concentration, and terpene composition in two Chemotype III (cannabidiol-dominant) varieties. Plants were subjected to moderate and severe water stress, and responses were assessed through biomass measurements, GC-MS analyses, and multivariate statistics. Water stress significantly influenced biomass allocation, with increased dry biomass but reduced harvest index, particularly under flowering-stage stress. Cannabidiol (CBD) content declined with increasing stress, while tetrahydrocannabinol (THC) levels increased under vegetative stress, indicating a stress-induced shift in cannabinoid biosynthesis. Cannabinol (CBN) levels also increased, suggesting enhanced THC degradation. Terpene composition was predominantly genotype-driven. PCA-MANOVA showed significant effects of variety, stress level, and their interaction, yet only minor volatiles were modulated by stress, while the most abundant terpenes remained stable across treatments, preserving the varietal aroma profile. These results underline the importance of genetic background and irrigation timing in determining cannabis yield and quality. Optimized water management is essential to ensure phytochemical consistency and sustainable production, especially in high-value medicinal and aromatic applications.