Manganese (hyper)accumulation within Australian Denhamia (Celastraceae): an assessment of the trait and manganese accumulation under controlled conditions

Background and aims: The genus Denhamia(Celastraceae) includes fifteen Australian species, many of which have a propensity for manganese (Mn) (hyper)accumulation. Among the key aims of this study were to: i) elucidate Mn accumulation in D. bilocularis, D. celastroides, D. pittosporoides and D. silvestris under controlled conditions; ii) examine the in situ distributions of Mn and other elements in tissues of i) above, and also in two other species growing in their natural habitat, i.e. D. silvestris and D. cunninghamii; iii) test numerous Denhamia herbarium specimens for Mn accumulation using portable X-ray fluorescence spectroscopy (XRF). Methods: Portable XRF and laboratory micro-XRF were used to examine Mn accumulation and foliar distribution patterns in several Australian Denhamia species. These techniques were variously applied to fresh field material and experimentally-raised plants treated with Mn (250 μg g⁻¹, 500 μg g⁻¹ and 1000 μg g⁻¹) and dry herbarium material. Results: The findings revealed D. bilocularis as a new Mn hyperaccumulator, with foliar Mn concentrations of up to 15,300 μg g⁻¹ in herbarium samples, and 13,700 μg g⁻¹ in experimentally grown plants. Laboratory μXRF maps consistently showed that foliar Mn accumulation was localized at the extremities of wild D. cunninghamii and D. silvestris leaves; whereas it was found in the vasculature of experimentally grown D. bilocularis and D. pittosporoides leaves. Conclusions: This study presents evidence that Mn accumulation across the Australian Denhamia species is taxonomically variable, however further work is required.