Xylomelum occidentale (Proteaceae) accesses relatively mobile soil organic phosphorus without releasing carboxylates
Date
2021
Authors
Zhong, H.
Zhou, J.
Azmi, A.
Arruda, A.J.
Doolette, A.L.
Smernik, R.J.
Lambers, H.
Editors
Gibson, D.
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Journal article
Citation
Journal of Ecology, 2021; 109(1):246-259
Statement of Responsibility
Hongtao Zhong, Jun Zhou, Azrul Azmi, André J. Arruda, Ashlea L. Doolette, Ronald J. Smernik, Hans Lambers
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Abstract
1. Hundreds of Proteaceae species in Australia and South Africa typically grow on phosphorus (P)-impoverished soils, exhibiting a carboxylate-releasing P-mobilizing strategy. In the Southwest Australian Biodiversity Hotspot, two Xylomelum (Proteaceae) species are widely distributed, but restricted within that distribution. 2. We grew Xylomelum 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 spectroscopy revealed which organic P forms X. occidentale accessed. 4. Xylomelum occidentale uses a strategy that differs fundamentally from that t ypical 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. 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 utilizing 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.
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2020 British Ecological Society