Kinetics of amino acid uptake by ectomycorrhizal roots

It is well established that ectomycorrhizal fungi can use amino acids as ni trogen and carbon sources, but data on the kinetic properties of amino acid uptake systems of ectomycorrhizal systems are scarce. Using C-14-labelled compounds we have determined the kinetics of uptake of amino acids by excis ed ectomycorrhizal roots for a range of distinct mycorrhizal types from thr ee tree species, beech, spruce, and pine. All mycorrhizal types examined to ok up amino acids via high-affinity transport systems (KM values ranging fr om 19 to 233 mmol m(-3)). A comparative analysis of kinetic parameters for uptake of amino acids and the ammonium analogue methylammonium showed that ectomycorrhizal roots have similar or even higher affinities (lower K-M val ues) for the amino acids, indicating that absorption of these organic forms of nitrogen (N) can contribute significantly to total N uptake by ectomyco rrhizal plants. Analysis of amino acid uptake by ectomycorrhizal roots coll ected along a European north/south gradient of increasing mineral N polluti on from northern Sweden to south Germany revealed no obvious trend in the u ptake capabilities for amino acids by ectomycorrhizal roots in relation to the location of the sampling site on this gradient. Rather, the fungal spec ies forming a particular morphotype was the factor determining uptake kinet ics. It can therefore be deduced that the species composition of the fungal community will contribute significantly to the functional diversity of a p opulation of mycorrhizal roots.