Capsicum annuum in vertical indoor farming: yield and capsaicinoid responses to reduced light and additional UV-A

Capsaicinoids, biosynthesized in pepper fruits (Capsicum annuum), are valuable compounds with diverse industrial applications. Their consistent production is essential but influenced by environmental factors such as light intensity and spectrum. Vertical indoor farming (VIF) systems offer precise environmental control over growing conditions, especially light, yet high energy costs often necessitate reduced light intensities. While peppers are light-demanding plants, their integration into VIF systems requires a balance between energy input and crop performance. To evaluate the feasibility of cultivating Capsicum annuum under energy-saving conditions, we investigated the effects of two reduced light intensities (250 / 500 µmol m⁻² s⁻¹) on fruit yield and quality across two chili pepper cultivars and one bell pepper in VIF conditions. Additionally, we assessed whether supplemental UV-A exposure at 500 µmol m⁻² s⁻¹ could enhance capsaicinoid accumulation.

Capsaicinoid content per unit dry fruit mass was not significantly affected by light intensity or UV-A as main effects. However, a significant interaction between cultivar and treatment indicated genotype-specific responses. Medium light intensity (500 µmol m⁻² s⁻¹) significantly increased net photosynthesis and fruit number, resulting in 33–57 % higher dry fruit yield (12.5–29.2 g_DW plant⁻¹) compared to the lower intensity (250 µmol m⁻² s⁻¹), and led to a corresponding increase in capsaicinoid yield per area, depending on cultivar. Light levels of 500 µmol m⁻² s⁻¹ are necessary to maximize yield and capsaicinoid output in VIF, while cultivar selection plays a critical role in determining compound accumulation.