IRON TOXICITY TO PLANTS IN BASE‐RICH WETLANDS: COMPARATIVE EFFECTS ON THE DISTRIBUTION AND GROWTH OF EPILOBIUM HIRSUTUM L. AND JUNCUS SUBNODULOSUS SCHRANK

Abstract

SummaryThe distribution of two common species of base‐rich wetlands, Epilobium hirsutum L. and funcus subnodulosus Schrank, as dominant species within a small, spring‐fed fen is correlated with high concentrations of iron present in the areas marked by superficial precipitated iron ochre. E. hirsutum was confined to the less iron‐rich parts. Other chemical variables (including P) showed little relationship to Epilobium distribution. In laboratory conditions, growth of E. hirsutum seedlings on waterlogged substrata from the same fen was much less on iron‐rich than lower‐iron soil, but J. subnodulosus seedlings showed no differential response. Growth of E. hirsutum on iron‐rich soil was slightly ameliorated by addition of P but remained low relative to that on low‐iron soil. Growth of J. subnodulosus was not increased by P addition.Growth of E. hirsutum was substantially increased by maintaining the iron‐rich soil at 80% field capacity (F.C) rather than in waterlogged condition, though on low‐iron soils greatest growth was found in waterlogged conditions. At 80% F.C. both iron and P were less available than when soil was waterlogged. Growth of J. subnodulosus seedlings was consistently greatest in waterlogged conditions. In solution culture, Epilobium hirsutum seedlings showed poor growth, ill health and death at high iron concentrations (> 50 mg l−1) whilst, although growth of J. subnodulosus seedlings was also reduced, they remained visually healthy. High iron concentrations caused rapid blackening and ultimate flaccidity and necrosis of E. hirsutum roots; such symptoms were absent from J. subnodulosus. These data suggest that high iron concentrations are detrimental to E. hirsutum, both in the field and laboratory, and that this is not just an indirect effect of iron upon other aspects of mineral nutrition. The significance of this to possible mechanisms of iron toxicity and waterlogging tolerance is discussed.