Recently, the National Aeronautics and Space Administration (NASA) laid out its vision for manned missions to Mars in 2030. To achieve this goal, NASA must establish reliable infrastructure including life support and a palatable source of fresh food (NASA 2015). Hydroponically grown sweetpotatoes are potentially a reliable food source for humans on extended space missions. NASA’s experience with continuous crop production in closed environments indicates that biological systems can be highly reliable, although failures of mechanical support systems regularly occur. Maintaining adequate food production will be the critical issue following a failure in a bioregenerative life support system since staple crops require in excess of 2 to 3 months to produce edible biomass (Hanford and Ewert, 2001). Perhaps, the most common type of failure is a temporary loss of electrical power and a partial power supply failure might result in low light but not complete darkness. Failures of the power supply system would likely be more common in remote locations such as on Mars, the Moon, or even Antarctica. When failure occurs there will be a time lapse before repairs are affected, which, depending on length of the time lapse, may impact plant responses. There is little data on the decreased performance and the tolerance limits of crop plants exposed to the unique perturbations that occur in closed, controlled environments. Failures are characterized by short-term, acute stress. Cumulative experience in controlled environments indicates that plants are surprisingly resilient to some types of control system failures, but sensitive to other failures, particularly during the reproductive stage of their life cycle (Dougher et al., 2000). Healthy crops produce a predictable, steady supply of oxygen and water. Interruption in crop metabolism alters these outputs and requires changes in the use of stored reserves.
Plants are well adapted to short periods of darkness because they have an 8- to 14-h dark period every night during the growing season. However, plants adapt to their photoperiod and the carbohydrate reserves are typically depleted near the end of the dark period. Thus, with an extended dark period, the respiration rate typically declines from lack of carbohydrates from active photosynthesis. Challa (1976) reported that at the end of the normal dark period, cucumber plants in continuous darkness metabolized structural compounds. Breeze and Elston (1978) reported that as little as a 6-h extension of the dark period caused significant reductions (compared with control plants) in photosynthesis when field bean plants were returned to the light, whereas Yentsch and Reichert (1963) found no signs of adaptation of photosynthesis in algae (Dunaliella euchlora) to lower light intensities after 40 h of dark exposure. Jones and Nelson (1979) found that root respiration of contrasting tall fescue genotypes decreased significantly after a 48-h dark period but that respiration of shoot meristems continued for the full 48 h and Costa et al. (1998) found that respiration rates of leaves of broad beans (Vicia faba) decreased steadily during 48 h of darkness. Robson and Parsons (1981) found that meristematic activity in uniculm barley continued forming new structural mass even during up to 50 h of darkness. These studies indicate that cell division continued in the absence of carbohydrate supply in at least some plants. Dougher et al. (2000) used canopy gas exchange to evaluate response and recovery of plant canopies of lettuce, spinach, radish, and tomatoes subjected to darkness of up to 14 d. They reported that canopy respiration was reduced to a minimum within 24 to 48 h of dark treatment. Plants that were subjected to a cold treatment during the dark periods recovered quickly when light was restored. In addition, carbon use efficiency (the ratio between the amount of carbon incorporated into dry matter to the amount of carbon fixed in gross photosynthesis) remained the same in all canopies regardless of temperature. In fact, Kubota and Kozai (1994) reported that low temperature storage (5–10 °C) of broccoli seedlings in combination with 2 µmol·m−2·s−1 PPF were important to preserve photosynthetic and regrowth abilities and dry weight of the plantlets. Thus, clearly, a few days of dark stress is not lethal to plants, however, plants do sustain some damage from extended darkness and the extent and rate of recovery has not been examined.
The objective of this research was to determine the impact of prolonged darkness on yield and growth responses of two sweetpotato cultivars grown hydroponically.
Breeze, V. & Elston, J. 1978 Some effects of temperature and substrate content upon respiration and the carbon balance of field beans (Vica faba L.) Ann. Bot. (Lond.) 42 863 876
Challa, H. 1976 An analysis of the diurnal course of growth, carbon dioxide exchange, and carbohydrate reserve content of cucumber. Agricultural Research Report. 861. Center for Agrobiological research, Wageningen, the Netherlands
Chard, J., Akula, G. & Bugbee, B. 2004 Failure analysis research summary: Mitigating the effects of prolonged darkness with low temperature and low light. 10 July 2016. <http://cpl.usu.edu/files/publications/factsheet/pub__6275308.pdf>
Costa, L.C., Morrison, J. & Dennett, M. 1998 Effects of water stress, temperature, prolonged darkness and pods on photosynthesis and respiration of individual leaves of Vicia faba Revista Ceres. 45 325 337
Dougher, T.A.O., Frantz, J., Klassen, S. & Bugbee, B. 2000 Failure analysis: Plant recovery from prolonged darkness. Proc. 4th Intl. Conf. Life Support and Biosphere Sci. p. 26
Hanford, A.J. & Ewert, M.K. 2001 Advanced life support systems modeling and analysis reference missions document CTSD-ADV 383 JSC-39502
Hoagland, D.R. & Arnon, D.J. 1950 The water-culture method for growing plants without soil. California Agr. Exp. Stn. Circ. 347, Univ. California, Berkeley, CA
Jones, R.J. & Nelson, C.J. 1979 Respiration and concentration of water soluble carbohydrate in plant parts of contrasting tall fescue genotypes Crop Sci. 19 367 372
Kubota, C. & Kozai, T. 1994 Low temperature storage of transplants at the light compensation point: Air temperature and light intensity for growth suppression and quality preservation Sci. Hort. 63 193 204
Morris, C.E., Loretan, P.A., Bonsai, C.K. & Hill, W.A. 1989 Moveable root contact pressure plate assembly for hydroponic system. U.S. Patent 4,860,490. 29 Aug. 1989. U.S. Patent Office, Washington, DC
Mortley, D.G., Loretan, P.A., Bonsai, C.K., Hill, W.A. & Morris, C.E. 1996 Growth responses of hydroponically grown sweetpotato tolerant intolerant of a continuous daily light period HortScience 31 209 212
NASA 2015 Journey to Mars: Pioneering next steps in space exploration. NASA Pub. No. 20151008-508
Robson, M.J. & Parsons, A.J. 1981 Respiratory efflux of carbon dioxide from mature and meristematic tissue of uniculm barley during eighty hours of continuous darkness Ann. Bot. (Lond.) 48 727 731
SAS Institute 2009 SAS user’s guide. Statistics, version 9.2 edition. SAS Institute, Cary, NC
Wilson, L.A. & Lowe, S.B. 1973 Quantitative morphogenesis of root types in the sweetpotato [Ipomoea batatas (L.) Lam] root system during growth from stem cuttings Trop. Agr. 50 343 345
Yentsch, C.S. & Reichert, C.A. 1963 Effects of prolonged darkness on photosynthesis, respiration and chlorophyll in the marine flagellate, Dunaliella euchlora Limnol. Oceanogr. 8 338 342