Acquisition of nitrogen by external hyphae of arbuscular mycorrhizal fungi associated with Zea mays L.

Abstract

SUMMARYThe objective of this study was to examine the ability of arbuscular mycorrhizal (AM) fungi to take up nitrogen from soil and transport it to the host plant. Maize {Zea mays L.) associated with Glomus intraradices Schenck and Smith or left uninoculated was grown in containers which were divided by a nylon net into a root compartment and a hyphal compartment. A 40 /im pore size nylon net was used to exclude plant roots while allowing fungal hyphae to grow into soil confined by the net. ^^N tracer was supplied either as inorganic N or as organic N to the hyphal compartment at a distance of 5 cm from the net.Inoculation with the AM fungus increased the '^N content of maize compared to the non-mycorrhizal controls when N was applied as (^^NHJ^SO^. However, there was no conclusive evidence that AM hyphae could derive N from organic "N sources. Most of the increased N uptake of mycorrhizal plants occurred by hyphal translocation from the hyphal compartment to the root compartment. Higher N uptake by mycorrhizal plants with access to the hyphal compartment was indicated by depletion of total ^'N in the soil of that compartment. Cutting the extraradical hyphae in the hyphal compartment in order to sever their connection with the host roots decreased the ^*N uptake of the maize plants. A time-course study with inorganic ^^N over 26 d showed that G. intraradices transported most of the '°N between 10 and 15 d after ^'N application, whereas the non-mycorrhizal control plants had a consistently low concentration of ^'N throughout the period of sampling.Nitrogen transport by external hyphae of three AM fungi, G. intraradices, Acaulospora laevis Gerdemann and Trappe and Gigaspora margarita Becker and Hall associated with maize, was further investigated. The results indicated that different isolates of AM fungi differ in the efficiency of hyphal N transport as a consequence of the different patterns of hyphal spread in the soil or of the different capacity for uptake by unit length of hyphae.

Nitrogen and phosphorus acquisition by the mycelium of the ectomycorrhizal fungus Paxillus involutus and its effect on host nutrition

“…This can be achieved by using culture vessels where hyphae are separated from the roots by a nylon net, and isolation of the hyphal contribution is attained by mass flow barriers such as air gaps, buffer compartments or perforated plastic barriers. Using such methods, long term N and P transport by external hyphae of arbuscular mycorrhizas has been quantified (Kothari, Marschner & Ro$ mheld, 1991 ;Li, George & Marschner, 1991 ;George et al, 1992 ;Frey & Schu$ epp, 1993 ;Pearson & Jakobsen, 1993 ;Johansen, Jakobsen & Jensen, 1994). To date similar data for ectomycorrhizas are lacking.…”

Effects of mycorrhizal colonization on biomass production and nitrogen fixation of black locust (Robinia pseudoacacia) seedlings grown under elevated atmospheric carbon dioxide

“…While elevated CO # stimulated the rate of N # fixation in non-mycorrhizal black locust seedlings, the rate of N absorption by roots was stimulated by CO # enrichment in mycorrhizal seedlings. Several studies have demonstrated that AM fungal hyphae are involved in the N nutrition of host plants, especially in the uptake of NH % + (Ames et al, 1983 ;Barea et al, 1987Barea et al, , 1989Kucey & Bonetti, 1988 ;Johansen et al, 1992Johansen et al, , 1994Frey & Schuepp, 1993). Frey & Schuepp (1993) found that inoculation with AM fungi increased the N uptake of maize plants primarily through hyphal translocation.…”

“…Several studies have demonstrated that AM fungal hyphae are involved in the N nutrition of host plants, especially in the uptake of NH % + (Ames et al, 1983 ;Barea et al, 1987Barea et al, , 1989Kucey & Bonetti, 1988 ;Johansen et al, 1992Johansen et al, , 1994Frey & Schuepp, 1993). Frey & Schuepp (1993) found that inoculation with AM fungi increased the N uptake of maize plants primarily through hyphal translocation. In an experiment with black locust, mycorrhizal fungi increased plant dependence on the uptake of soil N and decreased plant dependence on N # fixation (K. S. Olesniewicz & R. B.…”

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

“…However, in these systems the extent to which extraradical AMF hyphae can contribute to nutrient acquisition of plants remains difficult to determine because of unknown transport by diffusion and mass flow in the soil solution of mobile ions such as nitrate (Johansen et al, 1992(Johansen et al, , 1996Frey & Schu$ epp, 1993). To reduce diffusion and mass flow between the soil compartments, Faber et al (1991) used air gaps, paraffin wax or corn oil barriers, whilst Bethlenfalvay et al (1991) worked with a root-free soil bridge.…”