Growth response of highly tolerant Eucalyptus species to alkaline pH, bicarbonate and low iron supply

Abstract

The tolerance of 5 Eucalyptus species (E. gracilis F. Muell., E. halophila D. Carr & S. Carr, E. kondininensis Maiden & Blakely, E. loxophleba Benth. and E. platypus Hook var. heterophylla Blakely) to alkaline conditions, bicarbonate, and low iron availability was assessed in solution culture. All 5 species occur naturally in alkaline or saline soils in semi-arid Western Australia. A treatment solution of pH 9 and containing 10 mmol/L bicarbonate (HCO₃^–) reduced the rate of height increase and leaf and branch production of most species compared with a control of pH 6 with no bicarbonate. Iron concentration within the youngest fully expanded leaves was reduced for seedlings in the bicarbonate-pH 9 solution. Eucalyptus halophila was an exception, responding positively to the alkaline treatment in having taller seedlings, a greater leaf production, and maintaining a high leaf iron concentration. Eucalyptus gracilis, E. loxophleba and E. platypus had the highest growth rates within the alkaline treatment, but the slow growth and sequestering of iron by E. halophila provided this species with the greatest potential for tolerance. The relative growth and tolerance rankings of the species in solution culture were similar to those obtained in previous field trials on alkaline mine processing wastes. Field selection of species from calcareous or sodic sites, and laboratory screening under high bicarbonate conditions can identify species with the greatest potential for the rehabilitation of alkaline mine wastes and other damaged lands with soils of high pH.