INFLUX AND EFFLUX OF AMINO-ACIDS FROM ZEA-MAYS L ROOTS AND THEIR IMPLICATIONS FOR N-NUTRITION AND THE RHIZOSPHERE

The aim of the study was to investigate the ability of Zea mays L. roo ts to regulate the amount of free amino acids present in the rhizosphe re. The active uptake of amino acids was shown to conform to Michaelis -Menten kinetics. Comparison of amino acid-N and NO3-N kinetic paramet ers and soil solution concentrations showed that root uptake of free a mino acids from soil may contribute significantly to a plant's N budge t. The influx of amino acids also helps to minimize net C/N losses to the soil, and is therefore important in regulating the size of the rhi zosphere microbial population. Experimental data and a computer simula tion model of amino acid influx/efflux in a sterile solution culture, showed that roots were capable of re-sorping over 90 % of the amino ac ids previously lost into solution as a result of passive diffusion.