EFFECTS OF N SOURCE ON PH AND NUTRIENT EXCHANGE OF EXTRAMATRICAL MYCELIUM IN A MYCORRHIZAL RI T-DNA TRANSFORMED ROOT-SYSTEM

The influence of different N sources on medium pH variation and the ef fect of the external mycelium of arbuscular mycorrhizal fungi on nutri ent dynamics were studied using a two-compartment, aseptic Petri plate system. VA mycorrhizal, transformed roots of carrot (Daucus carota L. ) were cultured in the proximal compartment and external mycorrhizal m ycelium in the distal compartment. The medium in the distal compartame nt contained N either as NO3- or as NH4+. The pH and the anion and cat ion concentrations were measured every 15 days in filtrates prepared f rom the distal compartments. Thirteen weeks after colonization, there was a significant basification or a light acidification of the NO3- an d NH4+ medium, respectively. There was no change in NO3- concentration but a significant decrease in NH4+ concentration. Treatments containi ng N as NO3- showed no variation in cations such as Ca2+ and Mg2+ or a nions such as PO42-, and SO42- but showed significant increases in the concentration of K+. Treatments containing N as NH4+ showed no variat ion in cations or anions, except for increases in the concentrations o f K+ and Cl-.