Abstract
In food-productive river basins, ecosystems reliant on natural flows are affected by climate change and water removal. One such example is Australia’s Murray–Darling Basin (MDB), to which the ecologically important black box tree Eucalyptus largiflorens (Myrtaceae) is unique. Little is known about its mineral nutrition and response to flooding. A field study conducted at Hattah Kulkyne National Park on the MDB examined nutrient and Al distribution in mature and young foliage of trees whose status varied with respect to the presence of surface floodwaters. Black box is also of interest due to emerging evidence of its capacity to accumulate high foliar salt concentrations. Here, cryo scanning electron microscopy alone (SEM), combined with energy dispersive spectroscopy (SEM-EDS) and X-ray fluorescence (XRF) spectroscopy were applied to evaluate leaf anatomy and elemental patterns at the cellular and whole-leaf levels. Variation in whole-leaf elemental levels across flooded and dry trees aligned with known nutritional fluctuations in this drought-tolerant species reliant on occasional infrequent flooding. The microprobe data provide evidence of drought tolerance by demonstrating that extended conditions of lack of water to trees do not elicit leaf anatomical changes nor changes to leaf cellular storage of these elements. Foliar Na concentrations of ~2000–6000 mg kg–1 DW were found co-localised with Cl in mesophyll and dermal cells of young and mature leaves, suggesting vacuolar salt disposal as a detoxification strategy.
Highlights
The complexities of managing natural flows within river basin systems to balance their agricultural and native ecological productivities are exacerbated by the rising demand for food and adverse climatic trends (Poff et al 2003; Lynch and St Clair 2004; IPCC 2014; Grafton et al 2018)
Leaf chemical data (Table 1) indicate differences in S, Na, Fe, B, Co, Al, and Si concentrations associated with the flooding status and history of the tree(s) from which respective samples were taken
The trends in foliage Na concentrations with respect to flooding were observed for Fe, B, Co, and Al, where the flooding event appeared associated with elevation of these foliar levels at the second sampling
Summary
The complexities of managing natural flows within river basin systems to balance their agricultural and native ecological productivities are exacerbated by the rising demand for food and adverse climatic trends (Poff et al 2003; Lynch and St Clair 2004; IPCC 2014; Grafton et al 2018). One such case is the Murray–Darling Basin (MDB), Australia’s most agriculturally important and largest river catchment of over 1 Â 106 km, renowned for its significant natural habitats (Pittock and Finlayson 2011). Two field studies into its plant–soil nutritional dynamics (Fernando et al 2018a, 2021) provide the only insight into its mineral nutrition, along with emerging evidence of its ability to accumulate high Na concentrations
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