Effects of root temperature on uptake of nitrate and ammonium ions by barley grown in flowing-solution culture

Summary

Barley plants (Hordeum vulgare L.) grown from seed for 28 days in flowing solution culture were subjected to different root temperatures (3, 5, 7, 9, 11, 13, 17, 25°C) for 14 days with a common air temperature of 25/15°C (day/night). Uptake of NH₄ and NO₃ ions was monitored separately and continuously from solutions maintained at 10μM NH₄NO₃ and pH 6.0. Effects of root temperature on unit absorption rate s̄, flux f̄ and inflow Ī were compared. After 5 days s̄, f̄ and Ī increased with temperature over the range 3-ll°C for NH₄ ions and over the range 3–13°C for NO₃ ions, with little change for either ion above these temperatures. Q₁₀ temperature coefficients for NH₄ ions (3–13°C)were 1.9, 1.7 and 1.6 for s̄, f̄ and Ī, respectively, the corresponding values for NO₃ ions being 5.0, 4.5 and 4.6. For both ions, s̄, f̄ and Ī changed with time as did their temperature dependence over the range 3–25°C, suggesting that rates of ontogenetic development and the extent of adaptation to temperature may have varied among treatments.