Response of Common Ice Plant (<i>Mesembryanthemum crystallinum</i> L.) to Photoperiod/Daily Light Integral in Vertical Hydroponic Production

Common ice plant (<i>Mesembryanthemum crystallinum</i> L.) is a novel edible plant with a succulent and savory flavor emerging as new crop for greenhouse and plant factory growers. Currently very limited information is available on the response of ice plant to photoperiod and to daily light integral (DLI). The objective of this study was to determine the impact of photoperiod/DLI on the growth of ice plant for indoor vertical production. Four-week old seedlings of ice plant were transplanted into vertical hydroponic systems and given five photoperiod/DLI treatments: 8/6.3, 12/9.5, 16/12.7, 20/15.8, and 24/19.0 h/mol·m⁻²·d⁻¹. Sequential destructive harvests to determine plant growth occurred 14, 21, and 28 days after lighting treatments began. Plants performed better with increasing photoperiod/DLI from 8 h/6.3 mol·m⁻²·d⁻¹ to 20 h/15.8 mol·m⁻²·d⁻¹. By day 28, shoot fresh weight increased from 160 g to 639 g as the photoperiod/DLI increased from 8 h/6.3 mol·m⁻²·d⁻¹ to 20 h/15.8 mol·m⁻²·d⁻¹. The continuous lighting treatment, 24 h/19 mol·m⁻²·d⁻¹, showed a negative effect on the plant fresh weight (FW) and dry weight (DW). Light treatment did not have obvious effects on shoot:root ratio and macronutrient uptake except that potassium (K) uptake decreased slightly with increased photoperiod/DLI. Plants receiving higher photoperiod/DLI showed the same number of leaves (indicating the same development stage) but had smaller, thicker, and darker green leaves compared to lower photoperiod/DLI treatments. Leaf water content was not affected by light treatment up to 20 h/15.8 mol·m⁻²·d⁻¹ but decreased at 24 h/19 mol·m⁻²·d⁻¹. Further research is needed to separate the physiological response of increasing/continuous photoperiod from the response of increasing DLI.