Effects of Prolonged Reduced Pressure on the Growth and Nitrogen Content of Turnip (Brassica Rapa L.)

摘要

Photosynthetic plants are being considered for possible use in atmosphere regeneration and for food supply in extended manned space missions. The effects of potential spacecraft atmospheres on the growth of such plants is important in planning their use. This study investigates the effects of reduced total pressure on one plant, the turnip (Brassica rapa L.). During 21-day exposures to total pressures of 380 and 700 mm. Hg, seedlings and mature turnip plants were periodically harvested and analyzed. The rate of seedling growth, as measured by dry weight increase, was found to be slightly but significantly greater at 380 than at 700 mm. Pressure had no effect on either growth rate or top/root ratio of the older plants. The fact that percent dry weight (ratio of dry weight to fresh weight) was significantly less at 380 mm. suggested an effect of pressure on transpiration pattern. Percent total and protein nitrogen decreased with age at both pressures. In roots, the rate of decrease was unaffected by pressure, but in plant tops, the rate of decrease was significantly greater at 380 mm. This variance indicates a moderate but fundamental effect of pressure on plant metabolism and composition. It was concluded that the effects of reduced pressure were not sufficient to limit the future potential of plants in aerospace applications. (Author)