Canberra Times

I honestly didn’t know what stable isotopes were when I sat eating my first pie with the infamous Graham Farquhar.

To think I could have been working on seasonal forecasting systems for agricultural production in developing countries.  This was the alternative position on the table for my first postdoc. Instead I was lured to Canberra on a one-year contract to work in Adrienne Nicotra’s Lab on trait plasticity.  My plan was to use it as a stepping stone to work for CSIRO, reflecting my interests in agriculture.  My PhD was on improving the irrigation efficiency of dairy pasture systems. For one trial we were scheduling irrigation events using wireless soil moisture networks, with real cows grazing a real paddock of pasture.  I say real like it’s a novelty because it’s been a while since I hung out on a farm for my research.  The cows had a bad habit of trampling on the pods that were wiring us back the information and there was a lot of dodging of cow dung and trampled plants, but by pulsing the water delivery and allowing “room” in the soil profile to capture rainfall events (i.e. reduce through drainage) we were able to save up to 30% on irrigation water inputs.  From a plant physiological perspective, I was able to show that grasses were in fact pretty resilient to drought and could recover despite a 70% reduction in the leaf’s capacity to transport water.  There was a catch to this, and it is only now that the finer details are beginning to be worked out due to the lack of methods to be able to measure water transport in grass blades.  But that’s another story.  Fast-forward 6 years and my passion is now stable isotopes...and gumboots and K-line irrigators seem like a distant memory. 

I honestly didn’t know what stable isotopes were when I sat eating my first pie with the infamous Graham Farquhar (it would be months before I realised the relevance of pie-eating, and is a treasured memory I will be taking with me). My contract with Adrienne was about to run out and so I had begun fishing for my next job.  I’d heard on the grapevine that Graham had just landed himself a nice pot of money (SIEF).  Only, it turned out, it wasn’t public knowledge yet. I think it took all of 30sec post sending the email to Graham enquiring about his latest grant win before he was on the phone asking me how I had come to know this information - “you shouldn’t know about this, and who are you?”- and that’s how I ended up eating pie with him and the rest, as they say, is history.

Over the coming years, I was to learn about how there were different isotopes of carbon and oxygen consisting of different numbers of neutrons; isotopes with more neutrons are relatively heavier and so react and diffuse more slowly than lighter isotopes of the element. Consequently, the distribution of isotopes between reactants and products is altered during chemical and physical processes.  This is termed isotopic fractionation and has been used as a powerful tool to trace individual gross-fluxes at both the global scale and at the leaf level.  The theory to describe how photosynthetic gas exchange modifies the stable isotope ratio of atmospheric CO₂ (“photosynthetic discrimination”) was developed by Farquhar et al. (1982) for ¹³C and Farquhar et al. (1993) for ¹⁸O.  This mechanistic understanding has provided extensive insight into the diffusional limitations to CO₂ uptake at the leaf level (Evans et al. 1986); the tradeoff between carbon gain and water loss at the plant level (Farquhar & Richards 1984); and at the regional or global scale, a way to quantify the contribution of different components to ecosystem exchange (e.g. Francey et al. 1995; Keeling et al. 1995).  However, like most models, the predictions rely heavily on a priori information about key parameters that control the computation of isotopic discriminations.  And this has been the focus of my work – developing techniques to test the models and then applying them to estimate CO­­­­₂ diffusional limitations to assimilation rate and the saturation level of the vapour pressure inside the leaf.  This meant building a stable isotope laser spectroscopy lab from scratch; my biggest achievement to date. 

It had become a running joke in the lab that every Friday for the first year Hilary and I would feel the need to tweak its design…three lab moves later and it’s the most optimised system going around, so much so we’re rolling out our design to the University of Michigan.  I’d like to say it was all fun…but when you’re a postdoc with limited time, there were many moments where I wondered if I had opted for career suicide. Fortunately I had Hilary to make my “what if we did this” a reality and I can’t thank him enough for his unending optimism and determination.  There’s nothing like shared blood, sweat and tears to make life that more bearable!

So now that I know what swagelock fittings are, forgone the conceptual diagram for a mathematical definition and I am the owner a “I love isotopes” mug, I’ve packed my bags and moved to Switzerland to get a taste of holey cheese and mountains that make Ainslie look like pebbles; adding hydrogen isotopes to my tool bag; and going back in time to understand how plants are responding to climate change with the development of an isotopic marker for plant carbon balance. And I have many people to thank for making this a possibility, not least Graham. 

Graham is one exceptional human being. His intellect goes without saying; but it’s everything else that comes with being a part of his lab family that has made being at ANU an incredible experience that has exceeded all expectation. So, I leave ANU with optimism and fire in my belly, and humbled to even have the choice.

Meisha Holloway-Phillips

The Physiological Plant Ecology Group

University of Basel

• This article originally appeared in the RSB Newsletter, Issue 101, September 2018