THE BIOLOGY OF MYCORRHIZA IN THE ERICACEAE .17. THE ROLE OF MYCORRHIZAL INFECTION IN THE REGULATION OF IRON UPTAKE BY ERICACEOUS PLANTS

The role of the ericoid mycorrhizal endophyte Hymenoscyphus ericae (Read) Korf & Kernan in the regulation of iron uptake by ericaceous plants is investigated. Growth of the fungus is not inhibited in solution cultures containing a range (0–144 [ig ml−1) of iron concentration ([Fe]ext) typical of those obtained in extracts from heathland soil. Absorption of iron by the fungus occurs rapidly at low [Fe]ext but more slowly as [Fe]ext increases. Concentrations of iron in the mycelium ([Fe]mye), reach 6000μg g−1dry weight. Mycorrhizal (M) roots of Vaccinium macrocarpon Ait. and Calluna vulgaris L. (Hull) showed a very high affinity for iron at low [Fe]ext, a feature not shown by non‐mycorrhizal (NM) roots. The involvement of a hydroxamate siderophore in the absorption of Fe by M plants at low [Fe]ext is suggested. Concentrations of iron in shoots ([Fe]ext of NM plants of V. macrocarpon increase linearly with increasing [Fe]ext while those of M plants fall in the mid‐range of [Fe]ext relative to initial and final values. Ratios of [Fe]extto [Fe]ext are lower in M than in NM plants across the range of [Fe]ext examined. The extent of involvement of mycorrhizal infection in excluding the metal from shoots as [Fe]ext increases, is discussed, and the importance of the mechanisms of iron capture and storage in the root are assessed in terms of iron availability in natural heathlands. Copyright © 1990, Wiley Blackwell. All rights reserved