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Published July 24, 2020 | Version v1
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Xylomelum occidentale (Proteaceae) accesses relatively mobile soil organic phosphorus without releasing carboxylates

  • 1. University of Western Australia
  • 2. Chinese Academy of Sciences
  • 3. University of Adelaide


1. Hundreds of Proteaceae species in Australia and South Africa typically grow on phosphorus (P)-impoverished soils, exhibiting a carboxylate-releasing P-mobilising strategy. In the Southwest Australian Biodiversity Hotspot, two Xylomelum (Proteaceae) species are widely distributed, but restricted within that distribution.

2. We grew X. occidentale in hydroponics at 1 μM P. Leaves, seeds, rhizosheath and bulk soil were collected in natural habitats.

3. Xylomelum occidentale did not produce functional cluster roots and occupied soils that are somewhat less P-impoverished than those in typical Proteaceae habitats in the region. Based on measurements of foliar manganese concentrations (a proxy for rhizosphere carboxylate concentrations) and P fractions in bulk and rhizosheath soil, we conclude that X. occidentale accesses organic P, without releasing carboxylates. Solution 31P-NMR revealed which organic P forms X. occidentale accessed.

4. Xylomelum occidentale uses a strategy that differs fundamentally from that typical in Proteaceae, accessing soil organic P without carboxylates. We surmise that this novel strategy is likely expressed also in co-occurring non-Proteaceae that lack a carboxylate-exuding strategy, and plants in similar habitats. These co-occurring species are unlikely to benefit from mycorrhizal associations, because plant-available soil P concentrations are too low.

5. Synthesis. Our findings show the first field evidence of effectively utilising soil organic P by X. occidentale without carboxylate exudation and explain their relatively restricted distribution in an old P-impoverished landscape, contributing to a better understanding of how diverse P-acquisition strategies coexist in a megadiverse ecosystem.


Leaf chemistry data: elemental concentrations. Leaves were field-collected from natural habitats of Xylomelum species. This leaf_chemistry_data.csv file was created using Microsoft Excel 2013.

Funding provided by: Australian Research Council
Crossref Funder Registry ID:
Award Number: DP140100148, DP130100005



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10.1111/1365-2745.13468 (DOI)