The biology of mycorrhiza in the Ericaceae

summary 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.