Nutrient culture solutions

Table 1 Examples of Treatments Influencing Rhizodeposition Examined in Nutrient Culture Solutions...

Fish and microorganisms used as nutrients for fish suffer from a low surface tension of water. The lethal level of surfactant solutions was found to correlate with the surface tension of the culture solutions in which fish and microorganisms like daphnia and Cyclops were maintained. Lethality was at 49 mN/m. This effect possibly corresponds to the destruction of the respiratoric epithelia of the gills [196]. Consequently, knowledge about the so-called functional or primary biodegradation is important. 

Experiments to examine rhizodeposition can vary markedly in scale and complexity depending on the information required, the equipment available, and the plants concerned. In general, experiments to study exudates and other material lost from young roots are the simplest and are carried out in the laboratory under controlled conditions. Plants are grown in nutrient solution culture, sometimes with sand or other solid support systems, and compounds released into the culture solution are collected and analyzed chemically. The experiments are mainly short-term and the roots can be kept sterile if required. Techniques are also available to label plants growing in these systems with C and to monitor the presence of the isotopes in the rhizodeposits. 

The ability to change and control the composition of the nutrient solution and the relatively small size of the microcosms used enables manipulation of environmental variables and time-course studies of rhizodeposition to be made relatively easily. The influence of nutrient availability, mechanical impedance, pH, water availability, temperature, anoxia, light intensity, CO2 concentration, and microorganisms have all been examined within a range of plant species (9). A few examples to illustrate the continued interest in examining the effect of such variables on rhizodeposition in nutrient culture are given in Table 1. 

Inoculum. Inoculum of T, reesei QMY-1 was produced on the modified medium as described above but containing 1.5% glucose, with the nutrient salt solution diluted accordingly. For inoculation of each flask containing 5 g of substrate, 5 ml of 2-day-old culture was used. For SSF experiment, the inoculum was spread on the surface of the substrate. 

Most plants absorb NH4", K, NOa and Cl rapidly, whereas Ca, Mg and S04 are taken up slowly. This difference in rate of ion uptake can under some conditions have considerable effect on pH and on growth. If a complete culture solution contains nitrogen only as NOa its rate of uptake is more rapid than that of the cations with resulting rise in pH of the culture solution and a substitution of HCOa for NOa. Where all the N in a nutrient solution is present as NH4 it is taken up rapidly and as H is substituted for the NH4 the pH of the solution falls. Concunently the organic anion content of the plant material changes and the pH of the plant juice remains around 6. 

Abthoff J, Zahn W, Loose G, Hirschmaim A (1994) Serial use of palladium for three-way-catalysts with high performance. Motor Z 55(5) 292 Amon DI, Hoagland DR (1940) Crop production in artificial culture solutions and in soil with special reference to factors influencing yields and absorption of inorganic nutrients. Soil Sci 50 463-484... 

Complete solution changes for multiple phenolic acid treatments were used because phenolic acids supplied to seedlings in the nutrient culture system disappeared from the nutrient solution within 24-48 h (Blum and Dalton 1985 Blum and Gerig 2005). This was due to microbial metabolism, physical breakdown, and/or root uptake. Since we did not want to confound nutrient and phenolic acid effects, complete solution changes were made. An additional benefit of this approach was to reset phenolic acid concentrations to the initial treatment levels for each solution change. This was important since recovery of seedling processes occurred rapidly after phenolic acid depletion (Blum and Dalton 1985 Blum and Rebbeck 1989 Blum and Gerig 2005). 

Fig. 2.8 Change in absolute and relative rates of leaf expansion of 12 day-old cucumber seedlings as p-coumaric acid declines due to root uptake and microbial utilization in nutrient culture in the presence and absence of aeration, and when solutions were not changed or changed every 4 h. Figures reproduced from Blum and Gerig (2005). Figures used with permission of Springer Science and Business Media...

In summary the rate of depletion (i.e., root uptake and microbial utilization) varies with type phenolic acid present, concentration, pH, time of day, time of day of treatment, number of treatments, composition of phenolic acid mixtures, whether uptake is apoplastic or symplastic, phenolic acid-utilizing microbial populations present on roots and in the nutrient solution, and aeration. Phenolic acid treatments of seedlings in nutrient culture modify microbial populations on root surfaces (rhi-zoplane) and in the nutrient solutions. Once taken up by roots, phenolic acids were distributed throughout seedlings. Highest concentrations, however, were retained in the roots. 

In summary, observed effects of individual phenolic acids or phenolic acid mixtures were similar to what had been observed in nutrient culture but the response times and the magnitude of effects (see Section 2.4.8 for direct comparison) were slower and lower, respectively. Relative potencies of phenolic acids were lower when compared to nutrient culture. Increasing the number of phenolic acids in a mixture of phenolic acids reduced the concentrations of the individual phenolic acids required for a given percent inhibition. The presence of other readily available organic compounds (inhibitory or non-inhibitory) also reduced the concentration of phenolic acids required for a given percent inhibition. The addition of nitrate or nutrient solution reduced the inhibitory activity of phenolic acids. The inhibition of methionine, an amino acid, on the other hand was enhanced by the addition of nitrate. Finally phenolic acid effects were greater under acidic than under neutral conditions. 

Little is known about toxicity of ilhcit dmgs on plants. Mach and Livingston (1922) showed that lupine roots treated for 24 h with a 2.04% (v/v) cocaine solution causes complete growth inhibition. The lowest concentration of morphine showing toxicity to ladino clover seedlings in a complete nutrient culture was reported as 500 mg/kg (McCalla and Haskins, 1964). 

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