Effects of a localized supply of H₂PO₄, NO₃, Ca and K on the concentration of that nutrient in the plant and the rate of uptake by roots in young maize plants in solution culture.

Restricting the supply of a single nutrient to 1 of 4 maize roots resulted in a shoot conc. of that nutrient between that in the supplied and that in the non-supplied control plant. The calculated rate of root uptake (mmol/g day) of the locally supplied nutrient was higher in the supplied root of the treatment than in those of the supplied control plant. The negative relationship between shoot nutrient conc. (and sometimes root nutrient conc.) and the rate of root nutrient uptake indicates the existence of a negative feedback control by the shoot conc. on the rate of root uptake directed to a desired level in the shoot. The possible nature of the controlling signal is discussed. Increase in content of locally supplied nutrient in non-supplied roots indicates a net flux of nutrients from shoot to root. This flux concurs in non-supplied plants with decreasing shoot:root ratio and in treated plants with restored growth rate of the non-supplied roots. Total cation conc. (K + Na + Ca + Mg) was independent of treatment and type of tissue, but at K deficiency Na and Mg contributed more in the root and Mg more in the shoot. (Abstract retrieved from CAB Abstracts by CABI’s permission)