Detection and localization of aluminum and heavy metals in ectomycorrhizalNorway spruce seedlings

Norway spruce seedlings colonized with Hebeloma crustuliniforme were grown in growth pouches. After formation of ectomycorrhizas, the seedlings were e xposed to Al or the heavy metals Cd, Cu, Ni, or Zn at various concentration s for 5 weeks to estimate the detection limits of metals with X-ray microan alysis in the cryo-scanning electron microscope. When the lowest metal conc entrations (1 mM Al3+ , 0.1 mM Cd2+, 0.2 mM Cu2+, 0.5 mM Ni2+, 2 mM Zn2+) w ere applied, only Al and Zn were detected at low X-ray counts in the ectomy corrhizas. After application of 10-fold higher metal concentrations, distin ct metal accumulation patterns were observed. Cd was detected predominantly in the Hartig net, Al and Ni in the Hartig net and in the cell walls of th e cortex, and Zn in the Hartig net, the cortical cell walls and the fungal mantle. Cu was not detected at all. By combining X-ray microanalysis with a bsolute metal concentrations found in the roots, the estimated detection li mits of X-ray microanalysis were: Al greater than or equal to 0.86 mg g(-1) , Cd greater than or equal to 0.26 mg g(-1), Ni greater than or equal to 1. 30 mg g(-1), and Zn greater than or equal to 0.54 mg g(-1), whereas Cu was not detectable even at root concentrations of 0.47 mg g(-1). Treatments wit h the highest metal concentrations showed high X-ray counts of metals in ce lls of the stele but reduced concentrations of the macronutrients K, Mg, an d P in roots, indicating a possible disturbance of root and ectomycorrhizal function. (C) 2000 Elsevier Science Ltd. All rights reserved.