Research Projects

PhD Project 2013-2018

Supervisors: E/Prof Hans Lambers, School of Biological Sciences, The University of Western Australia; Assoc/Prof Peta Clode, Centre for Microscopy, Characterisation and Analysis, The University of Western Australia

Does calcium-enhanced phosphorus toxicity explain the absence of most Proteaceae species from calcareous habitats?

Articles:

• Hayes P.E., Clode P.L., Lambers H. (in press) Calcifuge and soil-indifferent Proteaceae from south-western Australia: novel strategies in a calcareous habitat. Plant and Soil (https://doi.org/10.1007/s11104-023-06297-9)

• Guilherme Pereira C.*, Hayes P.E.*, Clode P.L., Lambers H. (2021) Phosphorus toxicity, not deficiency, explains the calcifuge habit of phosphorus-efficient Proteaceae. Physiologia Plantarum 172(3): 1724–1738 (https://doi.org/10.1111/ppl.13384), * Contributed equally to this work

• Hayes P.E., Clode P.L., Guilherme Pereira C., Lambers H. (2019) Calcium modulates leaf cell-specific phosphorus allocation in Proteaceae from south-western Australia. Journal of experimental Botany, 70(15): 3995–4009 (https://doi.org/10.1093/jxb/erz156)

• Hayes, P.E.*, Guilherme Pereira, C.*, Clode, P.L., Lambers, H., 2019. Calcium-enhanced phosphorus toxicity in calcifuge and soil-indifferent Proteaceae along the Jurien Bay chronosequence. New Phytologist 221(2): 764-777 (https://doi.org/10.1111/nph.15447), * Contributed equally to this work

• Hayes, P.E., Clode, P. L., Oliveira, R.S., Lambers, H., 2018. Proteaceae from phosphorus-impoverished habitats preferentially allocate phosphorus to photosynthetic cells: an adaptation improving phosphorus-use efficiency. Plant, Cell and Environment 41(3): 605-619 (https://doi.org/10.1111/pce.13124)

Conference Proceedings:

• Hayes, P.E., Clode, P.L., Pereira, C.G., Lambers, H., 2019. Analysing Cell Level Allocation of Calcium and Phosphorus in Leaves of Proteaceae from South-Western Australia. Microscopy and Microanalysis 25: 1080–1081 (https://doi.org/10.1017/S1431927619006135)

• Clode, P.L., Hayes, P., Honvault, N., Lambers, H., 2015. A Multiscale Approach to Understanding Calcium Toxicity in Australian Proteaceae. Microscopy and Microanalysis 21: 1489–1490 (https://doi.org/10.1017/S1431927615008223)

• Clode, P.L., Hayes, P., Pereira, C.G., Lambers, H., 2014. Distribution of Calcium and Phosphorus in Leaves of the Proteaceae. Microscopy and Microanalysis 20: 1326–1327 (https://doi.org/10.1017/S1431927614008368)

Thesis:

• Hayes, P.E., 2018. Does calcium-enhanced phosphorus toxicity explain the absence of most Proteaceae species from calcareous habitats? Doctor of Philosophy, The University of Western Australia, Perth, Western Australia, Australia. (https://doi.org/10.4225/23/5b308848dc0c2)

Summary

The aim of this project is to discover the physiological basis of calcium (Ca) toxicity in the plant family Proteaceae and to determine the ecophysiological causes behind their distribution pattern in Australia, typically inhabiting low-phosphorus (P), acidic soils and avoiding calcareous soils. We propose that Ca toxicity is the primary factor in excluding Proteaceae from calcareous soils and that this occurs because, unlike most dicots that store P in epidermal cells, the P-efficient Proteaceae store P in mesophyll cells, where Ca is also stored, leading to their precipitation. It is further proposed that by shifting storage of Ca from mesophyll cells to epidermal cells some Proteaceae are able to avoid Ca toxicity and are therefore soil-indifferent. We will be growing plants in nutrient solutions and investigating the role of key soil factors (such as P, Ca, pH and bicarbonate levels) in influencing plant health, nutrient-acquisition and nutrient dynamics. Through further elemental X-ray microanalyses of leaf specimens we will also observe the cellular interactions of Ca and P under varying conditions and in a range of species from several continents, in order to quantitatively observe the storage of Ca and P in this unique plant family.

Importance

This research will further our understanding of Australia’s unique endemic plants, improving ecosystem conservation and restoration strategies and thus preserving our naturally high biodiversity. By understanding the soil conditions limiting the distribution of key native species this research will improve the successful use of native species for horticultural purposes, both privately and commercially, thus reducing local demands on the application of fertiliser and water, as compared to non-native species. This research also goes beyond Proteaceae and is equally relevant for understanding and managing lime-intolerant crop species, therefore providing benefits to agricultural research e.g., Lupinus albus.

Honours project

Supervisors: E/Prof Hans Lambers, School of Biological Sciences, The University of Western Australia; Assoc/Prof Etienne Laliberté, Department of Biological Sciences, The University of Montreal

Foliar nutrient concentrations and resorption efficiency in plants of contrasting nutrient-acquisition strategies along a 2-million-year dune chronosequence

Articles: 

• Hayes, P., Turner, B.L., Lambers, H., Laliberté, E., 2014. Foliar nutrient concentrations and resorption efficiency in plants of contrasting nutrient-acquisition strategies along a 2-million-year dune chronosequence. Journal of Ecology 102: 396-410 (https://doi.org/10.1111/1365-2745.12196)

 Summary

1. Long-term pedogenesis leads to important changes in the availability of soil nutrients, especially nitrogen (N) and phosphorus (P). Changes in the availability of micronutrients can also occur, but are less well understood. We explored whether changes in leaf nutrient concentrations and resorption were consistent with a shift from N to P limitation of plant productivity with soil age along a > 2-million-year dune chronosequence in south-western Australia. We also compared these traits among plants of contrasting nutrient-acquisition strategies, focusing on N, P and micronutrients. 

2. The range in leaf [P] for individual species along the chronosequence was exceptionally large for both green (103–3000 µg P g^-1) and senesced (19–5600 µg P g^-1) leaves, almost equalling that found globally. From the youngest to the oldest soil, cover-weighted mean leaf [P] declined from 1840 to 228 µg P g^-1, while P-resorption efficiency increased from 0% to 79%. All species converged towards a highly conservative P-use strategy on the oldest soils. 

3. Declines in cover-weighted mean leaf [N] with soil age were less strong than for leaf [P], ranging from 13.4 mg N g1 on the youngest soil to 9.5 mg N g1 on the oldest soil. However, mean leaf N-resorption efficiency was greatest (45%) on the youngest, N-poor soils. Leaf N:P ratio increased from 8 on the youngest soil to 42 on the oldest soil. 

4. Leaf zinc (Zn) concentrations were low across all chronosequence stages, but mean Zn-resorption efficiency was greatest (55–74%) on the youngest calcareous dunes, reflecting low Zn availability at high pH.

5. N2-fixing species had high leaf [N] compared with other species. Non-mycorrhizal species had very low leaf [P] and accumulated Mn across all soils. We surmise that this reflects Mn solubilization by organic acids released for P acquisition.

6. Synthesis. Our results show community-wide variation in leaf nutrient concentrations and resorption that is consistent with a shift from N to P limitation during long-term ecosystem development. High Zn resorption on young calcareous dunes supports the possibility of micronutrient co-limitation. High leaf [Mn] on older dunes suggests the importance of carboxylate release for P acquisition. Our results show a strong effect of soil nutrient availability on nutrient-use efficiency and reveal considerable differences among plants of contrasting nutrient-acquisition strategies.

Clément Gille - PhD student 2020-present

Co-supervisors: Assoc/Prof Patrick Finnegan, E/Prof Hans Lambers, Dr Kosala Ranathunge, School of Biological Sciences, The University of Western Australia

Physiology of phosphorus nutrition and ecosystem interactions in an extremely phosphorus-impoverished environment

Daniel Beeck - Honours student 2016-2017

Co-supervisor: E/Prof Hans Lambers, School of Biological Sciences, The University of Western Australia

The role of phenolic exudation by root systems of Banksia attenuata and Banksia laricina in determining species distribution in south-western Australia

Species that form cluster roots such as Banksias (Proteaceae) release different compounds into the soil to extract nutrients not readily available. Degradation of these exudate compounds by soil microorganisms represents a problem, as it can reduce nutrient-uptake. This study explores the release of phenolic and carboxylate compounds in the native Australian species Banksia attenuata, a widely distributed species, and Banksia laricina, a species with restricted distribution, found on soils believed to have particularly low microbial activity. Release of phenolics can inhibit the activity of soil microorganisms and is investigated here as an explanation for the contrast in species distribution.

Root exudates (phenolics and carboxylates) of hydroponically grown plants were analysed across four stages of cluster root development and for non-cluster roots. 

The exudation rate of phenolics was fastest in mature cluster roots of B. attenuata, being significantly greater than that in B. laricina. Banksia species show no exudative burst of carboxylates at the mature cluster-root stage. 

Banksia laricina may be restricted to low pH soils due to its slower release of phenolics, which could reduce its ability to access nutrients in soils with a high microbial activity. The lack of an exudative burst in mature compound cluster roots suggests they may be functioning differently to the previously studied simple cluster roots of other Proteaceae species. 

Nicolas Honvault - Intern student 2015

Co-supervisors: Assoc/Prof Peta Clode, Centre for Microscopy, Characterisation and Analysis, The University of Western Australia; E/Prof Hans Lambers, School of Biological Sciences, The University of Western Australia

Agriculture, Institut Polytechnique LaSalle Beauvais. Beauvais Cedex, 60026 France. 

Three month internship at CMCA (UWA), using novel techniques to investigate crystal formation and patterns in a range of Australian Proteaceae species. 

Conference Proceeding:

• Clode, P.L., Hayes, P., Honvault, N., Lambers, H., 2015. A Multiscale Approach to Understanding Calcium Toxicity in Australian Proteaceae. Microscopy and Microanalysis 21: 1489–1490 (https://doi.org/10.1017/S1431927615008223)

Shayanna Crouch - Honours student 2013-2014

Co-supervisor: E/Prof Hans Lambers, School of Biological Sciences, The University of Western Australia

 Foliar calcium concentrations of soil-indifferent Proteaceae species are the same on acidic and calcareous soils

Proteaceae species are common across the nutrient-impoverished soils of south-western Australia, and are characteristically able to mine the limited amount of phosphorus (P) from such soil. However, most Proteaceae species are excluded from younger calcareous soils with the reason behind this unknown. Hence, the aim of this study was to investigate the possible role of Calcium (Ca) in excluding Proteaceae species from calcareous soils. 

Leaf samples were collected and analysed for nutrient concentrations along the Jurien Bay dune chronosequence. Four soil-indifferent Proteaceae (two Banksia and two Hakea species) and four calcifuge Proteaceae (two Banksia and two Hakea species) were sampled along this sequence. A hydroponics glasshouse experiment was also conducted, in which four Banksia species were grown under varying Ca and P concentrations. 

Soil-indifferent species showed no difference in their foliar [Ca] when occurring on acidic or calcareous soils, even though the exchangeable soil Ca was much higher in the calcareous soils. Calcifuge species accumulated more Ca in their leaves compared to soil-indifferent species when growing naturally on the same low Ca acidic soils. 

Banksia sessilis had the highest survival rate in the glasshouse experiment, with most plants being harvested at 10 μmol P plant^-1 day-1 and 600 μmol Ca plant^-1 day^-1. The foliar [Ca] of B. sessilis significantly increased with increasing Ca supply, however the foliar [P] was the same under both P supplies of 10 and 100 μmol P plant^-1 day^-1, indicating an ability to down-regulate its P-uptake capacity. 

Results show difference in foliar [Ca] and [P] between soil-indifferent and calcifuge species, with calcifuge species showing much higher foliar [Ca] and lower [P]. Furthermore, soil-indifferent species showed no variation in their foliar [Ca], regardless of soil type, suggesting that soil-indifferent species are either better able to regulate their Ca uptake or the allocation of Ca to their leaf cells, whereas calcifuge species indicate little regulation in Ca accumulation.