Anthocyanins increase lighting cost in indoor lettuce production by reducing photosynthetic efficiency
Changhyeon Kim is a PhD student supervised by Dr. Marc W. van Iersel in the Department of Horticulture at the University of Georgia, Athens, Georgia, USA. His research focuses on development of a mechanistic model of lettuce dry matter accumulation to optimize lighting cost in controlled environment agriculture (CEA). He completed his BSc and MSc with a focus on fertigation for indoor crop production in the Department of Horticultural Science, Chungnam National University, Republic of Korea, in 2013 and 2015. In 2018, he obtained a second MSc degree with a focus on raspberry transformation in the Department of Plant Sciences, North Dakota State University, USA. Lighting, which accounts for up to 30% of total production cost, greatly impacts economic feasibility in the CEA industry. Lowering the lighting costs can be achieved by improving photosynthetic efficiency. The quantum requirement (QR, photons needed to fix 1 CO2) of C3 plants is typically estimated as 8-15 mol mol-1 depending on temperature and CO2 concentration. Anthocyanins, non-photosynthetic pigments, absorb photons and dissipate as heat for photoprotection, therefore presence of anthocyanins decreases number of photons for photosynthesis. However, the effect of anthocyanins on photosynthesis and QR is not clear. The objective of this study was to quantify the effect of anthocyanins in nine lettuce cultivars with a range of anthocyanins in their leaves. Greenhouse-grown lettuce was used to measure leaf absorptance, anthocyanin concentration, and leaf photosynthesis at different photosynthetic photon flux densities (PPFDs) to calculate QR. Anthocyanin concentration was positively correlated with absorptance, especially in the green part of the spectrum. Anthocyanins decreased the gross photosynthesis (Pg) at all PPFDs. Pg at a PPFD of 1500 µmol m-2 s-1 decreased by 69% as anthocyanin increased from 15.1 to 69.3 mg m-2. QR was 275 mol mol-1 in plants with high anthocyanin and at high PPFD. This was much higher than the typical estimates. Higher anthocyanin concentration and PPFD reduce photosynthetic efficiency and increase QR. The inhibitory effect of anthocyanin implies that environmental conditions in CEA should be manipulated to induce anthocyanin accumulation shortly before harvest to reduce lighting cost.
Changhyeon Kim won the ISHS Young Minds Award for the best poster at the IX International Symposium on Light in Horticulture, which was held virtually in Sweden in May-June 2021.
Changhyeon Kim, Department of Horticulture, University of Georgia, 1111 Miller Plant Science Bldg, Athens, GA 30605, USA, e-mail: email@example.com
The article is available in Chronica Horticulturae