Nitrogen supply and shading affect morphology and composition of the essential oil in marigold (Tagetes erecta L.)

Terrestrial plants are constantly exposed to multiple environmental signals that influence their metabolism. Among these signals, nitrogen (N) nutrition and light affect importantly diverse metabolic and physiological processes. Herewith the effects of N nutrition (8.47, 12.71 and 16.94 mg · L⁻¹ N) and shading percentages (0 and 70%) on plant morphology and chemical composition of the essential oil of marigold (Tagetes erecta L.) ‘Inca’ were assessed. Increasing N levels enhanced the number of secondary branches and the flower diameter, while shading reduced height of side branches, number of primary branches and opened flower buds. In leaves, flowers and stems, 15 different compounds were identified. In leaves, low and medium N levels and high light level increased the synthesis of ocimene, limonene and piperitone. As well, medium and high N doses, independently of the light level, stimulated the synthesis of caryophyllene and β-phellandrene in leaves. Nevertheless, increasing N doses and shading level decreased the synthesis of β-myrcene and α-pinene in leaves. In flowers, medium N level and high light intensity increased the synthesis of trans-pinene. Piperitone and verbenone were identified only in flowers of plants with high N doses and lower light intensity. In the stems, caryophyllene, piperitone and β-farnesene were more abundant with medium and high N levels. The interaction of study factors differentially affected both morphological variables and the composition of essential oil among organs studied. Therefore, N nutrition and light intensity are key factors that modify the morphology and composition of the essential oil in T. erecta.