Does manganese play a role in the distribution of the eucalypts?

Abstract

Two subgenera,Symphyomyrtus and Monocalyptus, within the genus Eucalyptus have been traditionally regarded as nutritionally different, although comparisons in the literature of foliar concentrations of nutrients in symphyomyrts and monocalypts do not support this hypothesis for the major nutrients N, P and K. However, the literature shows that concentrations of Mn in the leaves, stem and bark of symphyomyrts are consistently greater than those in monocalypts. The greater concentration of Mn in leaves of symphyomyrts compared with monocalypts was confirmed in both field and glasshouse studies and therefore appears to be a general response. However, in paired sites at the Black Range State Forest, there is no evidence from analyses of surface soils and subsoils that Mn is directing the distribution of symphyomyrts and monocalypts within the normal range of Mn availability. Further work should be directed towards the extremes of availability in the field. Because of the relatively low Mn content but relatively high availability of Mn in a sandy soil, monocalypts may be favoured over symphyomyrts. At the other extreme, a soil naturally high in Mn, such as basalt grasslands, locally waterlogged areas and soils immediately after f ire, may favour symphyomyrts over monocalypts. Concentrations of Mn in eucalypts are so high (800 mg kg ^–1 in green leaf-fall and up to 2800 mg kg ^–1 in leaves of glasshouse-grown seedlings) as to be within the toxic range for annual crop plants. The ability of eucalypts to accumulate Mn without showing toxicity should be further investigated.