Carbon dioxide concentration and nitrogen input affect the C and N storagepools in Amanita muscaria-Picea abies mycorrhizae

We studied the influence of elevated atmospheric CO2 concentration ([CO2]) on the vacuolar storage pool of nitrogen-containing compounds and on the gl ycogen pool in the hyphal sheath of Amanita muscaria (L. ex Fr.) Hooker-Pic ea abies L. Karst, mycorrhizae grown with two concentrations of ammonium in the substrate. Mycorrhizal seedlings were grown in petri dishes on agar co ntaining 5.3 or 53 mg N l(-1) and exposed to 350 or 700 mul CO2 l(-1) for 5 or 7 weeks, respectively. Numbers and area of nitrogen-containing bodies i n the vacuoles of the mycorrhizal fungus were determined by light microscop y linked to an image analysis system. The relative concentration of nitroge n in the vacuolar bodies was measured by electron energy loss spectroscopy (EELS). Glycogen stored in the cytosol was determined at the ultrastructura l level by image analysis after staining the sections (PATAg test). Shoot d ry 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 o f 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 th e non-mycorrhizal rootlets. When [CO2] was increased, the equilibrium betwe en storage of glycogen and N-containing compounds was reestablished.