Research Articles

Plant and Soil

, Volume 160, Issue 1, pp 1-9

First online:

Hyphal N transport by a vesicular-arbuscular mycorrhizal fungus associated with cucumber grown at three nitrogen levels

  • A. JohansenAffiliated withPlant Biology, Section, Environmental Science and Technology Department, Risø National Laboratory
  • , I. JakobsenAffiliated withPlant Biology, Section, Environmental Science and Technology Department, Risø National Laboratory
  • , E. S. JensenAffiliated withPlant Biology, Section, Environmental Science and Technology Department, Risø National Laboratory

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Abstract

Cucumis sativus L. cv. Aminex (F1 hybrid) was grown alone or in symbiosis with Glomus intraradices Schenck and Smith in containers with two hyphal compartments (HCA and HCB) on either side of a root compartment (RC) separated by fine nylon mesh. Plants received a total of either 100, 200 or 400 mg N which were applied gradually to the RC during the experiment. 15N was supplied to HCA 42 d after plating, at 50 mg 15NH4 +-N kg−1 soil. Lateral movement of the applied 15N towards the roots was minimized by using a nitrification inhibitor and a hyphal buffer compartment.

Non-mycorrhizal controls contained only traces of 15N after a 27 d labelling period irrespective of the amount of N supplied to the RC. In contrast, 49, 48 and 27% of the applied 15N was recovered in mycorrhizal plants supplied with 100, 200 and 400 mg N, respectively. The plant dry weight was increased by mycorrhizal colonization at all three levels of N supply, but this effect was strongest in plants of low N status. The results indicated that this increase was due partly to the improved inflow of N via the external hyphae. Root colonization by G. intraradices was unaffected by the amount of N supplied to the RC, while hyphal length increased in HCA compared to HCB. Although a considerable 15N content was detected in mycorrhizal roots adjacent to HCB, only insignificant amounts of 15N were found in the external hyphae in HCB. The external hyphae depleted the soil of inorganic N in both HCA and HCB, while the concentration of soil mineral N was still high in non-mycorrhizal containers at harvest. An exception was plants supplied with 400 mg N, where some inorganic N was present at 5 cm distance from the RC in HCA. The possibility of a regulation mechanism for hyphal transport of N is discussed.

Key words

15N Cucumis sativus Glomus intraradices hyphal N transport plant N status VA mycorrhiza