Temperature and water potential effects on physiological functions of sudangrass (Sorghum vulgare var. Piper) Public Deposited

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  • Temperature and water potential effects on the growth, transpiration, total nonstructural carbohydrate (TNC) content, and nutrient uptake of sudangrass (Sorghum vulgare var. piper) were investigated in laboratory experiments. The effect of nitrogen supply on the growth and nutrient uptake at constant soil water potential was also investigated in this study. Two week old seedlings were used for all experiments. Soil temperatures of 10.0, 15.6, 21.1, 26.7, 32.2 and 37.8 C were tested. Plants were grown at soil water potentials of -0.35 and -2.50 bars for 10 days using the polyethylene glycol semi-permeable membrane technique for controlling soil water potential. Air temperature remained constant at 26.7 C during these experiments. Air temperatures of 18.3, 22.8, 26.7 and 32.2 C were tested in a second series of experiments, with the soil water potential and soil temperature constant at -0.35 bars and 26.7 C. Further experiment.; were conducted with nitrogen levels in the nutrient solutions of 0, 10, 25 and 100 ppm. The soil temperature and soil water potential were kept constant in these experiments. Finally, the effect of soil temperature and soil water potential on plant water potential at soil water potentials of -0.35, -0.70, -1.50 and -2.50 bars was measured. Growth rate increased with soil temperature up to an optimum temperature, then decreased at higher temperatures for both shoots and roots at both soil water potentials tested. The highest growth rate was at 30 C for the shoots and 26 C for the roots. The rate was higher at -0.35 bars than at -2.50 bars for both shoots and roots. By varying the air temperature, the rate of growth was found to be highest at the air temperature of 26.7 C. The nitrogen level of 100 ppm in the nutrient solution produced the highest growth rate. The dry matter weight increased exponentially with time in all experiments. It was concluded that the soil temperature of 30 C, air temperature of 26.7 C and a soil water potential of -0.35 bars was optimal for sudangrass growth. Transpiration rates increased exponentially as a function of time for all treatments. Transpiration rates (cm³/day) increased as the soil temperature increased at both soil water potentials. The rate at -2.50 bars was lower than at -0.35 bars. The transpiration rate also increased with increasing air temperature independent of RH differences. An equilibrium content of N, P, K, Ca, Mg, S, Mn and Zn in the plant material at each combination of treatment variables was determined based on the assumption that equilibrium was attained as time progressed. The maximum concentration of N occurred at a temperature of about 30 C in both shoots and roots, while the concentration was lower at -0.35 bars than at -2.50 bars. The concentration of P increased with soil temperature, in the shoot, but reached a maximum at 30 C in the roots. The concentration at -0.35 bars was lower than at -2.50 bars. The concentrations of K, Ca and S were not significantly different at the two water potentials. The concentration of K was highest at about 30 C in both shoots and roots. The concentration of Ca was highest at about 22 C in both shoots and roots. The suflfur concentration of the shoots increased as soil temperature increased, but a maximum concentration in the roots occurred at 30 C. The concentration of Mn was highest at 26.7 C in the shoots and at 21.1 C in the roots. Concentrations of Mn at -0.35 bars were lower than at -2.50 bars. The Zn concentration increased as soil temperature increased for both shoots and roots. The concentration at -0.35 bars was lower than at -2.50 bars. In the experiments with air temperature as the variable the concentration of N in the shoots was highest at 26.7 C, but decreased in the roots as air temperature increased. The concentration of P decreased with increasing air temperature in both shoots and roots. The concentration of K increased with increasing air temperature in the shoots but decreased in the roots. The concentration of Ca was highest at 26.7 C in the shoots, and increased with increasing air temperature in the roots. The concentration of Mg in the shoots was highest at 26.7 C, while the concentration in the roots slightly decreased with increasing air temperature. The concentration of S decreased with increasing air temperature in both shoots and roots. The Mn concentration was highest at 26.7 C in both shoots and roots. The concentration of Zn increased as air temperature increased. The increase in the roots was greater than in the shoots. The concentration of N, P. Ca and Mg in both shoots and roots increased as the nitrogen level of the nutrient solution increased. The concentration of K in the shoots increased with increasing N level, but in the roots, a maximum concentration occurred at 25 ppm. The concentration of S in the shoots increased as the nitrogen level increased but decreased in the roots. Mn concentrations increased in the shoots but decreased in the roots with increasing nitrogen supply. The Zn concentration increased in the shoots, but decreased in the roots as the N level increased. The total nonstructural carbohydrate (TNC) content decreased as the soil temperature increased. The decrease was 10 percent at a soil water potential of -0.35 bars and 2 percent at a soil water potential of -2.50 bars as the soil temperature increased from 10.0 to 32.2 C. The TNC also decreased as the air temperature increased. The decrease was 8.3 percent as the air temperature increased from 18.3 to 32.2 C. This decrease was attributed to increased respiration and increased translocation from shoots to roots. The leaf water potential (Ψ[subscript c]) and osmotic potential (Ψ[subscript π]) decreased with time at all soil temperature and soil water potential combinations. The decrease was greater at low temperatures than at high temperatures for all soil water potentials. As the soil water potential decreased from -0.35 to -2.50 bars, the leaf water potential (Ψ[subscript c]) and osmotic potential (Ψ[subscript π]) decreased at all soil temperatures. The decrease is osmotic potential (Ψ[subscript π]) was greater than the decrease in leaf water potential (Ψ[subscript c]). The turgor pressure decreased with decreasing soil temperature, and slightly increased with decreasing soil water potential. The growth rate was correlated with turgor pressure. The relationship between turgor pressure and growth rate varied with soil temperature and soil water potential. It was concluded that this relationship may have been the primary growth controlling mechanism. The rate of nutrient uptake increased with increasing water uptake at both water potentials of -0.35 and -2.50 bars. The ion concentration in the transpiration stream was lower at -0.35 bars than at -2.50 bars. The concentration increased slightly with increasing soil temperature at both soil water potentials tested, but relatively more at -2.50 bars.
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