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Abstract
Analysis and research on the nutrition of some Australian native plants as well as diagnostic analysis of failed native plant gardens reinforces the view that manganese (Mn) availability is a major factor in the edaphology and cultivation of Australian native species. Yellow Kandosol soils on sandstone show a unique endemic floral assemblage. These soils show low total soil Mn levels of only 20–30 mg/kg. Despite this, endemic species such as Eucalyptus haemastoma and Acacia suaveolens show greater foliar Mn levels (around 291 and 389 mg/kg, respectively) than iron (Fe) levels, with Fe/Mn ratios as low as 0.14 and 0.27. During pot trial work on artificial soils created from crushed sandstone and green waste compost that were designed to research phosphorus (P) and calcium (Ca) nutrition, some interesting data on Mn uptake were collected. Levels of foliar Mn as high as 1250 and 389 mg/kg, respectively, accumulated in E. haemastoma and A. suaveolens when soils were artificially acidified to pH 4.7 (CaCl2) using ferrous sulfate. These Mn levels were associated with visible toxicity symptoms in foliage of E. haemastoma but not in A. suaveolens. Foliar Mn in both species showed a strong inverse correlation (R2 > 0.93) with soil pH. Previous research has shown that eucalypts from this floral assemblage are prone to Mn toxicity when grown in conditions of high soil Mn availability. Diagnostic analysis of soils and foliage for a client with horticultural problems in a native plant landscape showed severe chlorosis in a wide range of native species due to Mn deficiency induced by neutral soil pH (around 7.0 in CaCl2). Such soil pHs are considerably greater than those of the plant’s natural distribution. Despite apparently elevated soil P and the appearance of what looked like P toxicity, foliar P levels were not sufficiently elevated to conclude acute P toxicity but rather simple and severe Mn deficiency. The work suggests that induced Mn deficiency and toxicity may be underdiagnosed problems in the cultivation of many Australian native plants.