Graduate Thesis Or Dissertation
 

Ion uptake by wheat (Triticum aestivum VILL., Host) as a function of soil water suction and soil temperature

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  • The effects of soil temperature and soil water suction on the uptake of calcium, magnesium, and potassium by wheat (Triticum aestivum VILL., Host) were studied. Companion studies on uptake of nitrogen and phosphorus provided background for discussion of the results. Plants were grown in perlite slabs separated from an osmotic solution by a semi-permeable membrane. Five week old seedlings were used for the measurements made at root temperatures of 10.0, 18.3, 23.9, and 32.2°C, and soil water suctions of 0.35 and 2.5 bars. Air temperature remained constant at 23.9°C during these experiments. The dry weight of shoots and roots was determined at two-day intervals. Plant material extract was analyzed by atomic absorption spectrophotometry for concentrations of calcium, magnesium, and potassium. Rates of dry weight accumulation for both shoots and roots were highest when temperature of the root environment was about 24°C. The rate of growth was higher at a soil water suction of 0.35 bar than at 2.5 bars for all root temperatures tried. Concentrations of potassium, nitrogen, and phosphorus increased with increasing root temperature in both shoots and roots. By contrast, concentrations of magnesium were minimally affected by temperature differences; concentration increased slightly in the roots as temperature increased but remained the same in the shoots. Concentration of calcium in both shoots and roots decreased as temperature increased. This was attributed to a combination of ion interaction and temperature effects. The rate of uptake for all five elements, i. e. , calcium, magnesium, potassium, nitrogen, and phosphorus increased to a maximum rate and then decreased with increasing root temperature. The translocation of ions to the shoots was lowest for calcium. The fraction of total uptake translocated to the shoots was for: magnesium, 69%; potassium, 83%; nitrogen, 74%; phosphorus, 72%; and calcium less than 50%. Calcium content in the shoots was less than in the roots. The limited translocation of calcium to the shoots was attributed to its high degree of immobility. It was retained by the roots in relatively high concentration. The mineral concentration of plants grown at soil water suctions of 0.35 and 2.5 bars were not significantly different statistically while there was a significant reduction in the rate of plant growth at a soil water suction of 2.5 bars. As a result of the reduced growth rate at the higher suction the rate of ion uptake was also reduced even though the concentrations in the plant tissue at the two suctions were the same. Under the conditions of these experiments water availability affected plant growth apparently more by its effects on plant physiological functions other than mineral uptake.
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