Ammonium and Potassium Uptake by Citrus Roots

Abstract

Multiphasic kinetics were indicated for uptake of ammonium and potassium by intact citrus seedlings as measured by a continuous flow technique. Uptake at low concentrations, below 10"' M, was biphasic. The patterns for ammonium uptake by 60-day-old and 180-day-old seedlings were similar, but the rates of uptake per g dry weight of root were greater for the younger plants.

Kinetics of Manganese Uptake by Intact Citrus Seedlings

“…The increase in kinetic constants for Mn^+ uptake upon transition to higher phases agrees with that found for Zn^+ uptake by citrus seedlings (Hassan and Tang Van Hai 1976b) and for Cu^+ uptake by barley plants (Veltrup 1976), but differs from that found for Mn^+ uptake by sugarcane leaf tissue (Bowen 1969, as reanalysed by Nissen 1973.…”

“…Zn^+ uptake in citrus seedlings can also be represented by multiphasic isotherm (Hassan and Tang Van Hai 1976b). The clearly discontinuous patterns do not fit the dual or other continuous models of ion uptake.…”

“…Seeds of citrus (sour orange-Citrus aurantium L.) were planted in clay pots containing vermiculite. The seedlings grew for 2 months, and were irrigated with nutrient solution, before being transplanted to aerated nutrient solutions (Hassan and Tang Van Hai 1976a) with different concentrations of Mn^+ where they grew for another 20 days. The seedlings were then transferred to individual culture vessels through which the nutrient solution, minus micronutrients, were passed at a measured flow rate.…”

“…Manganese uptake was measured by monitoring the Mn^+ concentration before entering and after leaving the culture vessel. Details of experimental conditions are given elsewhere (Hassan and Tang Van Hai 1976b). The experimental solutions were labelled with carrier-free ^''Mn^+ and the radioactivity was measured by a Baird Atomic single channel scintillation counter.…”

Nutrient Use Efficiency in Citrus

“…It may be argued that sink strength may be one of the controlling factors governing downregulation of nitrogen uptake and also NUE (Yousse fi et al 1999(Yousse fi et al , 2000. Values for V max (on a root dry weight basis) for citrus were twice as high compared to estimated values for peach trees (Ran et al 1994 ) , but similar to those for ammonium uptake for citrus (Hassan and Van Hai 1976 ) . Nitrate uptake of citrus per unit root length was similar to those reported for maize (Heins and Schenk 1986 ) .…”