Abstract
At root temperature below 14 C the absorption of 15N from NH4+ greatly exceeded that from NO2− by tillers of Lolium multiflorum and Lolium perenne under conditions where pH, external concentration, plant N status, and pretreatment temperature were varied. There was a marked increase in the temperature sensitivity of NO3− transport below 14 C, irrespective of the temperature at which plants were grown previously. A marked increase in the temperature sensitivity was also seen for NH4+ transport, but this occurred at the lower temperature of 10 C. Pretreatment of roots at 8 C lowered this still further to 5 C. Above and below these transition temperatures the Q10 values for NO3− and NH4+ transport were similar. Thus, the increased absorption of NH4+ relative to NO3− at low temperatures seems to be related primarily to the difference in transition temperatures.
It seems possible that NO3− and NH4+ are absorbed through separate regions of the cell membrane differing in lipid composition and phase transition temperatures.
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Selected References
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