Frey Beat, Schüepp Hannes
Department of Phytopathology and Soil Microbiology, Swiss Federal Research Station, CH-8820 Wädenswil, Switzerland.
New Phytol. 1993 Jun;124(2):221-230. doi: 10.1111/j.1469-8137.1993.tb03811.x.
The 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 μm 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 ( NH ) 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.
本研究的目的是考察丛枝菌根（AM）真菌从土壤中吸收氮并将其转运至寄主植物的能力。将与根内球囊霉（Glomus intraradices Schenck and Smith）共生或未接种的玉米（Zea mays L.）种植在容器中，容器用尼龙网分隔为根系区室和菌丝区室。使用孔径为40μm的尼龙网来阻挡植物根系，同时允许真菌菌丝生长到网所限定的土壤中。在距离网5cm处向菌丝区室供应N示踪剂，形式为无机氮或有机氮。当以硫酸铵[（NH₄）₂SO₄]形式施用氮时，与未接种菌根的对照相比，接种AM真菌提高了玉米的氮含量。然而，没有确凿证据表明AM菌丝可以从有机氮源获取氮。菌根植物增加的氮吸收大多是通过菌丝从菌丝区室向根系区室的转运实现的。可进入菌丝区室的菌根植物对氮的吸收更高，这表现为该区域土壤中总氮的消耗。切断菌丝区室中的根外菌丝以切断它们与寄主根的连接，降低了玉米植株的氮吸收。一项为期26天的无机氮时间进程研究表明，根内球囊霉在施氮后10至15天转运了大部分氮，而未接种菌根的对照植物在整个采样期间氮浓度一直较低。进一步研究了与玉米共生的三种AM真菌，即根内球囊霉、平滑无梗囊霉（Acaulospora laevis Gerdemann and Trappe）和珠状巨孢囊霉（Gigaspora margarita Becker and Hall）的外部菌丝的氮转运。结果表明，由于菌丝在土壤中的扩展模式不同或单位长度菌丝的吸收能力不同，不同分离株的AM真菌在菌丝氮转运效率上存在差异。
