Vegetative growth, biomass allocation, and chlorophyll fluorescence of vanilla (Vanilla planifolia) as affected by light intensity and nitrogen supply

Abstract This study quantified the individual and interactive effects of photosynthetic photon flux (PPFD) density and nitrate-nitrogen supply on vegetative growth of Vanilla planifolia (V. planifolia) in a factorial experiment combining four PPFD levels (10‑208 µmol m⁻² s⁻¹) and six nitrogen concentrations (6.9‑60.5 mg NO₃⁻‑N L⁻¹) over 154 days. Light intensity was the dominant factor, affecting 16 of 20 parameters. Biomass gain saturated at 125 µmol m⁻² s⁻¹ (daily light integral ~ 5.4 mol m⁻² d⁻¹), while specific leaf area halved, indicating structural acclimation. Non-photochemical quenching rose 20‑fold without an increase in non‑regulated dissipation, consistent with regulated photoprotection. Nitrogen optimised biomass production efficiency at approximately 50‑56 mg L⁻¹, and leaf nitrogen saturated near 2.1‑2.2% dry mass. Light × nitrogen interactions were scarce (4 of 20 parameters), indicating that nitrogen demand was largely independent of light within the range tested. PSII fluorescence parameters responded exclusively to light; Y(NO) was unresponsive to both factors. The results provide the first PPFD and nitrogen dose‑response data for V. planifolia and, as an outcome from this soilless system, support a target of 125 µmol m⁻² s⁻¹ PPFD for highest growth and 50–56 mg NO₃⁻-N L⁻¹ for optimal nitrogen-use efficiency in vegetative cultivation.