Transport of N-15 from a soil compartment separated by a polytetrafluoroethylene membrane to plant roots via the hyphae of arbuscular mycorrhizal fungi

We studied the transport of N-15 from a soil compartment separated from a p lant root compartment by a hydrophobic polytetrafluoroethylene (PTFE) membr ane to plants in the presence and absence of arbuscular mycorrhizal fungi ( AMF). We have previously shown that this type of membrane efficiently inhib its mass flow and diffusion of mobile ions in the soil solution in an abiot ic system but can be penetrated by the hyphae of mycorrhizal fungi. Mycorrh izal tomatoes (Lycopersicon esculentum) colonized by Glomus mosseae were gr own at two N fertilizer concentrations in a root compartment. A PTFE membra ne was placed between the root compartment and an adjoining soil compartmen t that was inaccessible to the roots but accessible to the AMF hyphae (hyph al compartment). Additional N was applied to the hyphal compartment using u niformly N-15-labelled NH4NO3. There was a Aux of N-15 from the hyphal comp artment to the plants el en in the absence of mycorrhizal fungi. However, t his flux was much higher in mycorrhizal plants, which had much higher N con centrations in their shoots and roots than did the non-mycorrhizal control plants. This was particularly apparent when the root compartment had a low N fertilizer concentration. Of the total N content of mycorrhizal plants, c . 42 and 24%, at the low and high N fertilizer concentrations, respectively , were estimated to originate from the hyphal compartment by transport thro ugh AMF hyphae. In the presence of mycorrhizal fungi, the flux of N-15 was about three times higher than in their absence. The results show that AMF c an access a soil compartment separated by a PTFE membrane, and can contribu te substantially to N uptake by plants.