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Abstract
The development of controlled environments in the early 1950’s with sufficient radiation intensity to obtain vigorous plant growth initiated a rapid explosion of environmental research. It was an explosion that provided a decade or a decade and one-half of real excitement in plant physiology. Many light, temperature and carbon dioxide interactions were unraveled, as it was possible to vary one factor and hold all other factors of the environment constant. The controlled environment was a must for plant physiologists if their work was to have real validity.
Abstract
It is a pleasure to be introducing this symposium to provide an appreciation of the real interest that NASA has in using plant systems for life support in space. The symposium is directed toward providing details on what is planned, and what is actually underway, in this effort. It is a program that has been titled CELSS, Controlled Ecological Life Support System, and involves a tremendous breadth of horticultural areas—areas that can require the expertise of nearly everyone in horticulture, as suggested in Fig. 1. The project must start with plant propagation, probably tissue culture propagation, and involve all aspects of environmental optimization of growth, breeding of adapted cultivars, nutrient, possibly nutrient film, feeding techniques (NFT) and automated nutrient recycling, contaminant control in the atmosphere, pathogen control in the nutrient solution, precise growth modeling for regulation of the system, maximization of harvest index to reduce inedible portions, efficient food processing, balanced diets, and complete recycling of all wastes. The expertise of all types of horticulturists is needeed if this project of NASA is to be successful.
A nutrient delivery system developed for plant growth in space provides a unique system for maintaining a constant, slightly-negative water tension for plant research. The system involves the use of multiple porous stainless steel tubes positioned 4 cm apart in shallow trays (44 cm long, 32 cm wide and 8 cm deep), and then covered with a 4 cm layer of fine medium. Nutrient solution is recirculated through the porous tubes under -5 cm (water head) of negative pressure maintained with a siphoning procedure. Potatoes grown with negative pressures were compared to growth in similarly constructed trays that were maintained on a slant and solution added to the upper end of the trays and drained from the lower end. The same nutrient solution was recirculated through the trays of each treatment and maintained at a pH of 5.6. A microcultured plantlet of Norland cv. was transplanted into each tray. The negative pressure produced plants with less total plant dry weight, leaf area, branches, and stolons but increased biomass partitioning into tubers. The data suggest that this small constant negative water pressure regulates assimilate partitioning to encourage production of tubers.
Plants of three potato (Solanum tuberosum L.) cultivars, Denali, Norland, Russet Burbank, were grown under CO2 concentrations of 500, 1000, 1500, 2000 ppm at each of 16 and 20C temperature levels. In all three cultivars, total plant dry weight on day 35 after transplanting was greater under 1000, 1500, and 2000 ppm CO2 than under 500 ppm CO2 at both 16 and 20C, and greater at 20C than at 16C under each of the CO2 concentrations. At 20C total dry weight was highest under 2000 ppm CO2 for all cultivars whereas at 16C total dry weight was highest under 1000 ppm CO2 for Denali and Norland, but highest under 1500 ppm CO2 for Russet Burbank. The similar pattern was seen with tuber dry weight except that in Russet Burbank the weight was greater at 16C than at 20C under 500, 1000, and 1500 ppm CO2. Also, for all cultivars specific leaf weight (SLW) under 1000, 1500, and 2000 ppm CO2 was much higher than under 500 ppm CO2 at 16C, but only slightly higher than under 500 ppm CO2 at 20C. The SLW was higher at 16C than at 20C under all CO2 concentrations. This study demonstrates that growth responses of potatoes to CO2 concentrations differ with temperature.
Three nutrient culture experiments were conducted to determine the responses of potatoes (Solanum Tuberosum L.) to various solution pH levels with NO3, NH4, and mixed NO3/NH4 (1/1) at the same total N of 4 mM. The pH levels were maintained at 4, 5, 6, and 7 with NO3 or NH4, and at 4, 4.5, 5, 6, 6.5, 7 with mixed N. In each of the experiments, Norland plants were grown for 28 days after transplanting. With mixed N, plant growth as total dry weight, leaf area and tuber number was essentially similar at pH 4.5 to 7, and decreased only at pH 4. However, with either NO3 or NH4 growth peaked at a particular pH level, pH 5 and 6 respectively, and was significantly reduced at other pH levels with severe stunting at pH 7. With mixed N, the concentrations of total N in shoots were similar at pH 4 to 7 whereas, with either N form, the concentrations of total N were higher at particular pH levels, pH 4 and 5 with NO3 and pH 7 with NH4. The concentrations of P, S, Ca, Mg, and Mn in shoots were similar at pH 4 to 7 with mixed N, but varied at certain pH levels with either NO3 or NH4. The results indicate that the useful pH range for nutrient uptake and plant growth is broader with mixed N than with either NO3 or NH4.
The effects of various NH4-N/NO3-N ratios on growth and mineral accumulation in potatoes (Solanum tuberosum cv. Norland) were investigated using a nutrient film technique. Plants were grown for 35 days after transplanting at six NH4-N/NO3-N mixtures of 0/100%, 20/80%, 40/60%, 60/40%, 80/20%, and 100/0% with the same total N concentration of 4 mM. All mixed N treatments significantly increased total and tuber dry weights, plant size, leaf area, and specific leaf area as compared to either NH4 or NO3 alone. Plant growth was better with NO3 alone than with NH4 alone. Compared with mixed N treatments, total N concentrations in shoots were lower with either N form alone whereas total N in roots was lower only with NO3 alone. With increased percentages of NH4, root nitrate N concentrations decreased, and reduced N increased. The NO3 alone treatment increased concentrations of Ca, Mg, Fe and Mn, and reduced concentrations of P, S, Cl, B, Zn and Cu in shoots as compared with NH4 and mixed N treatments. It is concluded that a proper maintenance of both NH4 and NO3 forms can potentially promote growth and yield in potatoes.
A modified nutrient film technique (NFT) with a shallow granite medium was developed to control the flow rate and concentration of nutrients to which potato plants were subjected. Flow rates were 2, 4, and 8 ml per minute with balanced nutrient concentrations at 25, 50, and 100% (0.6 to 2.4 dS m-1 conductivity) of modified Hoagland's solution that was not recycled. Potato growth was greatest and about equal at 4 ml of 50% solution and at 8 ml of 25% solution. In shoots, accumulation of P, Fe, and Mn increased with both increasing concentrations and increasing flow rates. Zn accumulation decreased with increasing concentrations, and Ca, Mg, and Cu accumulation decreased with increasing flow rates. Accumulation of K, S, and B differed little with either concentrations or flow rates. In tubers, the differences resulting from variations in concentrations and flow rates were less than in shoots but accumulation patterns were similar except Ca and Mg accumulation did not decrease with increasing flow rates and K accumulation increased with both increases in concentration and increases in flow rate.
Abstract
Lettuce plants, Lactuca sativa L. cv. Meikoningen, grown in growth chambers and exposed to 14CO2 for 15 minutes in light of 21.5 klx accumulated measurable amounts of labeled metabolites within the lacticifers within 1 hour and a maximum amount within 48 hours. Latex in the outer leaves, inner heart leaves and roots was uniformly labeled at all time periods studied. A significantly greater amount of labeled metabolites accumulated under a light level of 21.5 klx following the initial assimilation period, than under a light level of 10.75 klx or under darkness. This research indicates that with high light conditions accumulation of metabolites in the latex is increased and this could be significant in encouraging tipburn, a physiological injury of lettuce.
Abstract
The influence of atmospheric moisture levels of 85% and 50% relative humidity (RH) (3.5 and 11.6 mb saturation vapor deficit respectively) at 20°C for 16:8 long day (LD) cycle on butterhead lettuce, (Lactuca sativa L. cv. Meikoningen), during a growth period of 4 weeks from seeding, was studied in organic soil and liquid cultures. Significantly faster growth rates were evident on plants developing under 85% RH than under 50% in both soil and liquid culture with the largest increases occurring with plants grown in soil culture. The higher humidity level increased leaf number 15%, leaf size 30%, dry weights 62%, and leaf water contents from 93% to 94%. The differences in leaf number and dry weight equalled about 2 days growth difference at 4 weeks after seeding. The density of stomata was greater on plants grown under 50% RH but the total number of stomata per leaf under the 2 humidity levels was the same. The leaf resistance was significantly higher on plants grown under 50% than under 85% RH. The principle significance of high humidity level during growth of lettuce is the production of larger marketable heads with a higher water content in a slighly reduced period of time.
Abstract
An attempt has been made here to condense the great volume of literature for many different air pollutants and from many different plant systems. Only those responses that have been reported for several species are emphasized and our discussion is limited to responses obtained with intact plants.