Two PhD positions advertised

Two 3-year PhD scholarships are available for bright and energetic candidates to join our group. These scholarship are open to Australian or international applicants.

One scholarship (ref. 2018446 here) is for a project that fits within the framework of “plant functional ecology” (see our Welcome and Projects pages to see what that means to us), with the topic to be arrived at through discussion. Depending on the successful candidate’s research strengths the project could involve field-based ecological or physiological studies, glasshouse-based experiments, analyses of trait-environment relationships, theory development – or (ideally) some combination of these approaches. The focus should be on understanding the ecological strategies of species in non-agricultural and non-horticultural settings, and on elucidating broad trends across species, not within single species.

The second scholarship (ref. 2018445 here) is associated with the project, Optimal photosynthetic traits on ecological time-scales. This position will include a substantial fieldwork component, measuring ecophysiological traits in natural vegetation at sites in eastern Australia. Possible topics include (1) The role of soil nutrition in shaping photosynthetic trait variation; and (2) The interplay between plant hydraulic and photosynthetic strategies. Within that framework, the PhD candidate would be expected over time to develop their own research directions. Previous experience in measuring plant physiological properties would be highly regarded.

Essential criteria for both positions include (1) Demonstrated ability to conduct high quality, independent research as part of a completed Masters-level research degree with substantial thesis component. (2) Clear record of academic excellence as an undergraduate. (3) Excellent verbal and written communication skills. (4) Must be able to commence at Macquarie University before 15th December 2018. Experience in writing up previous research for journal publication will be highly regarded.  From people meeting all of these criteria (more details at Rating Scholarship Applicants website) we can invite some number to discuss detailed research possibilities with a view to applying for the scholarships via the Online Application System. Initial inquiries should be directed to Professor Ian Wright (ian.wright@mq.edu.au).

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Two postdoc positions advertised

We have just advertised two three-year postdoc positions. Both positions are aimed towards candidates with a strong publication record, and with 3 or more years relevant experience, post-PhD (“Level B”, in Australian terminology). For someone truly exceptional there is possibility to appoint as a “Senior Research Fellow” (Level C). One position is for an experienced field ecologist or physiologist with expertise in photosynthesis. The other is for someone with a flare for data analysis. Below are the links to the position descriptions on our university website. The closing date for applications is 12th April.

Postdoctoral Research Fellow in Data Analysis and Modelling (plant functional ecology) – level B/C

Postdoctoral Research Fellow in Plant Functional Ecology (field ecophysiologist) – Level B/C

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Two big papers from late 2017

We published two papers in late 2017 that reflected our twin interests of developing first-principles theory for plant function and investigating plant form and function at global scale, and the power of putting these two approaches together:

  • Wang H, Prentice IC, Cornwell WK, Keenan TF, Davis TW, Wright IJ, Evans BJ, Peng C (2017). A universal model for carbon dioxide uptake by plants. Nature Plants 3:734-741.
    • This analysis continued the work on “least-cost” theory for photosynthesis (Wright et al 2003 Am Nat; Prentice et al 2014 Ecol Lett), successfully confirming at global scale the optimality-based theory for environmental control of CO2 drawdown during photosynthesis (ci:ca). Next we twinned this approach with photosynthetic coordination theory (Maire et al 2012, and others), allowing us to articulate least-cost theory with a LUE-based model for GPP. This allows us to make first-principles predictions for GPP as a function site climate and elevation, with no need for separate functions for each Plant Functional Type. We envisage this approach as sitting at the core of a ‘next-generation’ vegetation model, to be developed over several years.
fig 1 least cost v6

In least-cost theory (Wright et al. 2003; Prentice et al. 2014) the optimal ratio of N and water use for photosynthesis is set by the ratio of their unit costs for acquisition and use. Asat is the light-saturated rate of photosynthesis. Left: purple dots represent situations where transpiration is relatively expensive or, equally, where carboxylation is relatively cheap, corresponding (as predicted, middle panel) to cold sites (a,c) and to dry sites (b, d). Right: Predicted versus observed Ci:Ca (Wang et al. 2017). The dataset (Cornwell et al. in review) is for 3653 species with long-term Ci:Ca estimated from leaf stable carbon isotope ratios.

  • Wright IJ, Dong N, Maire V, Prentice IC, Westoby M, Díaz S, Gallagher RV, Jacobs BF, Kooyman R, Law EA, Leishman MR, Niinemets Ü, Reich PB, Sack L, Villar R, Wang H & Wilf P (2017). Global climatic drivers of leaf size. Science 357:917-921.
    • In this project we revisited a century-old question (is there a latitudinal gradient in leaf size?) and a 50-year old question (what are key climatic controls over leaf size variation?). Compiling data for several thousand species around the world, we quantified the latitudinal gradient (larger leaves near the equator) and also interactive effects of site moisture and temperature (and irradiance) as drivers of leaf size variation. Next we demonstrated a new and simple approach to leaf energy balance theory that focuses on maximum leaf size rather than mean trends, giving the ability to make quantitative predictions for maximum feasible leaf sizes as a function of site climate, with broad support at global scale. A key finding was that, overall, the risk of radiative frost damage may be just as influential in limiting leaf sizes as the role of day-time overheating (the traditional” explanation). Leaf size variation has strong consequences for leaf temperature and water use, both key variables in the photosynthetic models that underpin global vegetation models. Is there a role for optimality-based theory for leaf size variation in the next generation of global models?
Wright_et_al_Fig_4 (converted from PDF)

Predicted geographic trends in maximum leaf size. Each grid cell is color-coded according to the smaller of the two predictions for maximum leaf size (day-time, night-time; see Fig. S13 in Wright et al 2017). Areas coded the deepest shade of blue are those where there may be no effective thermal constraint on maximum leaf size: because sufficient water is generally available for effective transpirational cooling, and warm night-time air temperatures prevent leaves from suffering radiative frost damage.

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New paper: leaf economics across the Triassic-Jurassic boundary!

The ratio of leaf dry mass to leaf area (LMA) is a key trait for understanding the leaf economic strategies of plant species, but how can we estimate LMA for species long since gone extinct? Given very nicely preserved fossil leaves, one method is to directly measure the leaf area, and then divide it by an estimated value for leaf dry mass. Back in 2007 we (led by Dana Royer) showed that this estimated value can be calculated, using biomechanical principles, from the width of the petiole – the structure that physically supports the leaf blade.

In a new paper (led by postdoc Wuu Kuang Soh) we have revisited this question of estimating LMA from fossils, this time showing that LMA can be directly estimated from measurements of leaf cuticle thickness. Cuticles fossilize beautifully, for example leaf stomata may be exquisitely preserved. In this work we first showed that cuticle thickness (CT) is a good predictor of LMA across a variety of broad-leaved gymnosperm species (many growing in the Royal Botanic Gardens here in Sydney). fig1a

Next, Jenny McElwain (Dublin) sent out a set of fossil leaves from a well-studied sequence in Greenland that includes fossil beds either side of the Triassic-Jurassic boundary (a mass extinction event that occurred approx. 200 million years ago). We developed a method for carefully cutting cross-sections of these fossils, then predicted the LMA of each leaf using the predictive equation derived for living species.

 

fig1d

Cross-section of a fossil Ginkgoites leaf from the Late Triassic period

Because Jenny and collaborators had already quantified the relative abundance of the various fossil species, we were able to estimate community-weighted mean LMA values, and so ask whether there were clear shifts in plant ecological strategies across the T-J boundary. In short, it looks like the extreme climatic conditions of the T-J boundary selectively knocked out low-LMA species, species that presumably had faster metabolic rates. The Early Jurassic plant communities were not only made up of completely different species to those from the Late Triassic, they also had more stress-tolerant, “conservative” leaf economic strategies.

 

Royer DL, Sack L, Wilf P, Lusk CH, Jordan GJ, Niinemets U, Wright IJ, Westoby M, Cariglino B, Coley PD, Cutter AD, Johnson KR, Labandeira CC, Moles AT, Palmer MB & Valladares F (2007). Fossil leaf economics quantified: calibration, Eocene case study, and implications. Paleobiology 33:574-589.

Soh WK, Wright IJ, Bacon KL, Lenz TI, Steinthorsdottir M, Parnell AC, McElwain JC (2017). Palaeo leaf economics reveal a shift in ecosystem function associated with the end-Triassic mass extinction event. Nature Plants 3:17104.

 

 

 

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Congratulations Tim!

Congratulations to Tim Maher for being awarded his Masters (Research), and for achieving a top-band also. Time’s thesis was titled “Withstanding heat waves: Proteomic analysis of adaptive thermotolerance in Eucalyptus grandis seedlings”. His supervisor team consisted of Rachael Gallagher, Mehdi Mirzaei and Ian Wright.

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Rachael awarded an ARC DECRA!!

Hearty congratulations to Rachael Gallagher who has been awarded a prestigious 3-year Discovery Early Career Researcher Award by the Australian Research Council. The title of Rachael’s proposal is  “Life on the edge: how species interactions shape range boundaries”.

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The new plant growth chambers have arrived!

Exciting times! In late 2015 we secured funding to replace a number of aging controlled-environment growth chambers with state-of-the-art Conviron chambers, replete with light, temperature, humidity and [CO2] control. The new chambers arrived today. Over the next few weeks these will be installed and this very important area of the Plant Growth Facility will be refurbished. This follows on from other major works carried out over the last year, including replacing glasshouse lighting systems with high-efficiency (and very bright) LED lights, and replacing aging glasshouse side-walls and roofs. Now, to do some research!

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One of the chambers, arriving by crane

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Masood (Facility Manager), modelling one of the new Conviron chambers

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The beautiful pink glow of LED lighting

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