Effects of hypobaria, hyperoxia, and nitrogen form on the growth and nutritional quality of lettuce.

The objectives of this research were to investigate the impact of hypobaria, hyperoxia, and nitrogen form on the growth and nutritional quality of plants. Pre-culture 20-day-old lettuce (Lactuca sativa L. var. Rome) seedlings grew for 25 days under three levels of total atmospheric pressure (101, 54, and 30 kPa), two levels of oxygen partial pressure (21 and 28 kPa), and two forms of nitrogen (NO3N and NH4N). The ratios of NO3N to NH4N included 3: 1, 4: 0, 2: 2, and 0: 4. The nitrogen quantity included two levels, i.e. N1, 0.1 g N kg-1 dry matrix and N2, 0.2 g N kg-1 dry matrix. The growth status of lettuce plants in different treatments differentiated markedly. Regardless of the nitrogen factor, the growth status of lettuce plants treated with total atmospheric pressure/oxygen partial pressure at 54/21 was equivalent to the treatment of 101/21. Under the hypobaric condition (54 kPa), compared with 21 kPa oxygen partial pressure, hyperoxia (28 kPa) significantly inhibited the growth of lettuce plants and the biomass (fresh weight) decreased by 60.9%-69.9% compared with that under 101/21 treatment. At the N1 level, the sequence of the biomass of lettuce plants supplied with different ratios of NO3N to NH4N was 3: 1 > 4: 0 > 2: 2 > 0: 4, and there were higher concentrations of chlorophyll and carotenoid of lettuce plants supplied with the higher ratio of NO3 to NH4. At the N2 level, the effects of different ratios of NO3N to NH4N on lettuce plants were similar to those at the N1 level. The high nitrogen (N2) promoted the growth of lettuce plants such as 54/21/N2 treatments. Both form and nitrogen level did not affect the stress resistance of lettuce plants. Hypobaria (54 kPa) increased the contents of N, P, and K and hyperoxia (28 kPa) decreased the content of organic carbon in lettuce plants. The high nitrogen (N2) improved the content of total N and the N uptake. The ratios of NO3N to NH4N were 4: 0 and 3: 1, lettuce could absorb and utilize N effectively. This study demonstrated that hyperoxia (28 kPa) inhibited the growth of lettuce plants under the hypobaric condition (54 kPa), and high level of nitrogen (0.2 g N kg-1 dry matrix) and NO3N: NH4N at 3: 1 markedly enhanced the growth, the contents of mineral elements and the nutritional quality of lettuce plants.

Operation overview of a biological waste treatment system during the 4-crew 180-day integrated experiment in the controlled ecological life support system (CELSS).

Waste management and treatment is vital to health care and material circulation, especially in the Controlled Ecological Life Support System (CELSS) with finite resources for long-duration manned space missions. A closed ecological-cycle integrated 4-crew 180-day experiment platform was established to investigate the key technologies such as effective cultivation of higher plant, water treatment and recycling, waste management and treatment. In this study, generated waste during the integrated experiment was classified as renewable and non-renewable waste. The renewable waste including all crew feces and part of inedible plant biomass were treated in a biological system where the aerobic composting technology was utilized. The performance in relation to degradation effect, phytotoxicity and nutrient evaluation was examined during the continuous 180 days. The long-term operation results displayed that 96.26 kg feces and 74.4 kg wheat straw were treated, and 90.6 kg compost product was discharged in nine batches. The microbial community variation was analyzed and Firmicutes, Actinobacteria and Proteobacteria enriched in the compost. The phytotoxicity of compost was examined by seed germination index (GI) and GI of Chinese cabbage ranged from 88% to 132% for all batches. Compared to grown in vermiculite only, the lettuce yield increased 19% when grown in a mixture of vermiculite and processed compost. The summary of this work will be helpful to facilitate future applications of aerobic composting technology as the bio-based waste treatment technology in CELSS.