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- Author or Editor: T. W. Tibbitts x
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.
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.
Foliar concentrations of starch and nutrients (N, K, Ca, Mg, P and S) were determined in three potato (Solanum tuberosum L.) cvs Denali, Norland and Russet Burbank grown for 35 days under 500, 1000, 1500 and 2000 ppm CO2 at each of 16 and 20C. The plants were grown in 8-liter plastic pots containing commercial peat-vermiculite mix under controlled environments with 450 μmol m-2 s-1 PPF for 12 h photoperiod. The average starch concentrations in three cultivars increased from 4.4% to 18.5% d.w. with increased CO2 and decreased temperature. The starch concentrations were linearly related to specific leaf weight with a R2 of 0.97. With or without starch correction, the concentrations of N, Ca, Mg, P and S on dry weight basis tended to decrease with elevated CO2, and reduced temperature whereas the concentration of K did not change with the CO2 levels and was higher at 16C than at 20C. Combined mineral concentrations of N, Ca, Mg, P and S, before or after starch correction, were negatively related to the starch concentrations up to 14%, and then changed only slightly with higher starch concentrations. These results will be discussed in terms of potential growth enhancement from CO2 supplementation.
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.
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.
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.
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.