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 effect of the external mycelium of arbuscular mycorrhizal fungi on nutrient 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 mycelium in the distal compartment. The medium in the distal compartament contained N either as NO₃ ^– or as NH₄ ⁺. The pH and the anion and cation concentrations were measured every 15 days in filtrates prepared from the distal compartments. Thirteen weeks after colonization, there was a significant basification or a light acidification of the NO₃ ^– and NH₄ ⁺ medium, respectively. There was no change in NO₃ ^– concentration but a significant decrease in NH₄ ⁺ concentration. Treatments containing N as NO₃ ^– showed no variation in cations such asCa²⁺ and Mg²⁺ or anions such as PO₄ ^2–, and SO₄ ^2– but showed significant increases in the concentration of K⁺. Treatments containing N as NH₄ ⁺ showed no variation in cations or anions, except for increases in the concentrations of K⁺ and Cl^–. Accepted: 7 March 1996