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Carbon dioxide concentration and nitrogen input affect the C and N storage pools in Amanita muscaria–Picea abies mycorrhizae

Katarzyna Tarnau (1), Andrea Berger (4), Anja Loewe (2), Werner Einig (2), Rüdiger Hampp (2), Michel Chalot (3), Pierre Dizengremel (3) and Ingrid Kottke (4)

1. Institute of Botany of the Jagiellonian University, ul. Lubicz 46, 31-512 Krakow, Poland / 2. Eberhard-Karls-Universität Tübingen, Botanisches Institut, Spezielle Botanik/Mykologie, Auf der Morgenstelle 1, D-72076 Tübingen, Germany / 3. Laboratoire de Biologie Forestière, Universitè Henri Poincaré, Nancy I, BP 239, F-54506 Vandoeuvre-lés-Nancy, France / 4. Eberhard-Karls-Universität, Tübingen, Botanisches Institut, Physiologische Ökologie der Pflanzen, Auf der Morgenstelle 1, D-72076 Tübingen, Germany / Received November 6, 1999

Summary

We studied the influence of elevated atmospheric CO₂ concentration ([CO₂]) on the vacuolar storage pool of nitrogen-containing compounds and on the glycogen pool in the hyphal sheath of Amanita muscaria (L. ex Fr.) Hooker–Picea abies L. Karst. mycorrhizae grown with two concentrations of ammonium in the substrate. Mycorrhizal seedlings were grown in petri dishes on agar containing 5.3 or 53 mg N l^–1 and exposed to 350 or 700 μl CO₂ l^–1 for 5 or 7 weeks, respectively. Numbers and area of nitrogen-containing bodies in the vacuoles of the mycorrhizal fungus were determined by light microscopy linked to an image analysis system. The relative concentration of nitrogen in the vacuolar bodies was measured by electron energy loss spectroscopy (EELS). Glycogen stored in the cytosol was determined at the ultrastructural level by image analysis after staining the sections (PATAg test). Shoot dry weight, net photosynthesis and relative amounts of N in vacuolar bodies were greater at the higher N and CO₂ concentrations. The numbers and areas of vacuolar N-containing bodies were significantly greater at the higher N concentration only at ambient [CO₂]. In the same treatment the percentage of hyphae containing glycogen declined to nearly zero. We conclude that, in the high N/low [CO₂] treatment, the mycorrhizal fungus had an insufficient carbohydrate supply, partly because of increased amino acid synthesis by the non-mycorrhizal rootlets. When [CO₂] was increased, the equilibrium between storage of glycogen and N-containing compounds was reestablished.

Keywords: CO₂, EELS, glycogen, nitrogen, photosynthesis, vacuole.

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