Honours Project Opportunities in Plant Ecosystem Function

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Dr Charles Warren

How do Australian plants cope with phosphorus deficiency?

Plants have multiple strategies to cope with phosphorus deficiency such as modifications of root architecture, mycorrhizal associations, and exudation of compounds that increase phosphorus availability in the soil [1, 2]. An additional strategy that is only just receiving attention is replacement of phospholipids with non-phosphate containing membrane lipids.

This exciting and novel project will determine the role of lipids in tolerance of phosphorus deficiency. Such information can then be used to develop agricultural and forest crops that are more tolerant of phosphorus deficiency. This project could test the hypotheses that there is genetic variation in lipid profiles of species differing in tolerance to phosphorus deficiency, and the capacity for lipid replacement is greater in species tolerant of phosphorus deficiency. Field studies will make use of the wide diversity of soil types in the Sydney basin to collect data from plants that occur on P-deficient soils (e.g. sandstone-derived) or P-replete soils (e.g. basalt-derived). Greenhouse studies will use a sub-set of species from the field experiment that will be grown with a range of phosphorus supply from sufficient to strongly deficient.

Do plants, bacteria or fungi win in competition for N?

Recent technological advances are providing new insights into the N cycle and are challenging the traditional views of what limits N supply to plants [3-5]. The traditional view of the N cycle is based on two key assumptions: plants can take up only inorganic N (nitrate and ammonium), and plants compete poorly with soil microbes. Both of these assumptions are looking increasingly shaky.

This project will examine the key question of who wins in competition for N. Is it plants bacteria or fungi? We will use isotope labelling and biomarkers to partition fluxes of N among bacteria, fungi and plants. These biomarker methods have been used to estimate fluxes through bacteria and fungi, but have not simultaneously measured uptake by plants. Isotopic analysis of biomarker compounds will link identity (biomarker), biomass (concentration of the biomarker) and activity (isotope assimilation). This experiment may involve a combination of lab/greenhouse studies and field work in Tasmania.

Metabolomics of stress-tolerant species

This project will use metabolomics to uncover what it takes for plants to tolerate abiotic stress. The hypothesis-free metabolomic philosophy and improvements in analytical technologies are re-shaping our view of plant responses to drought and temperature stress. Early studies on abiotic stress focused on single metabolic pathways or classes of molecules and highlighted accumulation of metabolites as compatible solutes that function to maintain turgor under water stress [6]. Recent ‘omics’ studies have shown global changes in gene expression and metabolite composition and thus we now know that abiotic stress has widespread (and in many cases unexpected) metabolic effects [7, 8]. To place data in an ecological context and increase the generality of findings this project will not rely solely on a handful of traditional model species (e.g. Arabidopsis, Medicago, Populus). Instead it will make use of pre-existing genotypic variation (e.g. of species that differ in tolerance of water or nutrient stress) to explore the diversity of mechanisms plants have for coping with their environment.

References

  1. Lambers, H., et al., Root structure and functioning for efficient acquisition of phosphorus: Matching morphological and physiological traits. Annals of Botany, 2006. 98(4): p. 693-713.
  2. Lambers, H., et al., Plant nutrient-acquisition strategies change with soil age. Trends in Ecology & Evolution, 2008. 23(2): p. 95-103.
  3. Chapman, S.K., et al., Plants actively control nitrogen cycling: uncorking the microbial bottleneck. New Phytologist, 2006. 169: p. 27-34.
  4. Schimel, J.P. and J. Bennett, Nitrogen mineralization: challenges of a changing paradigm. Ecology, 2004. 85(3): p. 591-602.
  5. Chapin, F.S., P.A. Matson, and H.A. Mooney, Principles of terrestrial ecosystem ecology. 2002, New York: Springer-Verlag. 436.
  6. Morgan, J.M., Osmoregulation and Water-Stress in Higher-Plants. Annual Review of Plant Physiology and Plant Molecular Biology, 1984. 35: p. 299-319.
  7. Rizhsky, L., et al., When Defense pathways collide. The response of Arabidopsis to a combination of drought and heat stress. Plant Physiology, 2004. 134(4): p. 1683-1696.
  8. Urano, K., et al., Characterization of the ABA-regulated global responses to dehydration in Arabidopsis by metabolomics. Plant Journal, 2009. 57(6): p. 1065-1078.