Ground Based Study on Culturing Garlic as a Source of Vegetable Food and Medicine in Space - Growth and Ajoene Accumulation in Garlic Plants Cultured with Different CO 2 Regimes

Abstract

Life support and effective countermeasures against damaging space radiation for humans on long-duration space missions will be highly dependent on the amount of food and efficient conversion of CO2/O2. The cultivation of fresh vegetables enriched in phytomedicine is an alternative option for keeping crews' health and recycling of CO2 in a closed environment. A whole garlic plant cultured hydroponically is edible and a rich source of medicinal compound, carbohydrates, proteins and vitamins. Garlic plants were cultured for 60 days at 400 (control), 450, 800 and 900 µmol mol-1 carbon dioxide in controlled environment chambers to study growth and ajoene accumulation. Lighting was provided with fluorescent lamps as a 12 h photoperiod with 450 µmol m-2 s-1 PPFD. Fresh and dry mass accumulation of each parts of garlic plants were significantly increased by increasing the CO2 levels from 400 to 900 µmol mol-1. Fresh mass in bulbs, leaves and roots were 28.6, 66.3 and 92.2 g per plant, respectively, and 1.9, 1.8 and 2.0 times, respectively, greater at 900 µmol mol-1 CO2 than at 400 µmol mol-1 CO2. Transpiration rate and stomatal conductance were decreased by increasing the CO2 levels while water use efficiency and relative chlorophyll contents were increased. The concentrations of ajoene accumulation were significantly increased with increasing of CO2 levels from 400 to 800 µmol mol-1 but no significant increase of ajoene accumulation was observed with increasing CO2 level from 800 to 900 µmol mol-1. Total ajoene accumulation in bulbs, leaves and roots were 2.3, 2.6 and 2.6 times, respectively, greater at 900 µmol mol-1 CO2 than at 400 µmol mol-1 CO2. The results indicate that elevated CO2 can increase ajoene accumulation as well as biomass production and water-use efficiency in garlic plants.