Root foraging in the leguminous zinc hyperaccumulator Crotalaria novae-hollandiae from Queensland, Australia
Fuyao Chen A , Philip Nti Nkrumah B , Roger H. Tang B and Antony van der Ent
B C *
A Environment Science and Spatial Informatics, China University of Mining and Technology, Xuzhou City, China.
B Centre for Mined Land Rehabilitation, Sustainable Minerals Institute, The University of Queensland, St Lucia, Qld, Australia.
C Université de Lorraine-INRAE, Laboratoire Sols et Environnement, 54000 Nancy, France.
Australian Journal of Botany 71(4) 167-174 https://doi.org/10.1071/BT22033
Submitted: 24 March 2022 Accepted: 25 February 2023 Published: 30 March 2023
© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution 4.0 International License (CC BY)
Abstract
Context: Root foraging by hyperaccumulator plants in response to patchily distributed metals has been observed in several obligate hyperaccumulators, but it is not known whether facultative hyperaccumulators respond similarly.
Aims: This study investigated the root-growth behaviour in the leguminous zinc (Zn) hyperaccumulator Crotalaria novae-hollandiae compared with the non-accumulating Crotalaria cunninghamii in response to localised soil Zn enrichment in the soil to observe foraging versus avoidance responses.
Methods: We conducted rhizotron experiments in which we exposed the Crotalaria species pair to juxtaposed treatments, which were either homogenous (each half of the treatments containing same Zn concentrations) or heterogenous (different Zn concentrations in each half of the treatments). The Zn concentrations were 0 μg Zn g−1 (control), 2000 μg Zn g−1 and 5000 μg Zn g−1 in the form of zinc carbonate).
Key results: We found that none of the treatments had significantly different rooting density and root biomass, regardless of the Crotalaria species. This finding contrasts with increased root proliferation in Zn-rich patches found for other obligate hyperaccumulator species.
Conclusions and implications: The no-preference root response towards Zn in Crotalaria may partly explain the facultative hyperaccumulation mechanism displayed by these species. This root response towards Zn may ultimately affect Zn phytoextraction efficacy when utilising Crotalaria species in a heterogenous Zn soil substrate. These findings highlight the need for rhizosphere investigations prior to field phytoextraction applications.
Keywords: Crotalaria, hyperaccumulation, metal tolerance, microXRF, phytoextraction, root avoidance, root foraging, zinc.
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