For a full publication list, see Belinda Medlyn’s Google Scholar page

Spotlight on: Student Papers

We are very proud of the excellent work carried out by our PhD students. Read on to find out some highlights:

Kumarathunge DP, Medlyn BE, Drake JE, Tjoelker MG, Aspinwall MJ, Battaglia M, Cano FJ, Carter KR, Cavaleri MA, Cernusak LA, Chambers JQ, Crous KY, De Kauwe MG, Dillaway DN, Dreyer E, Ellsworth DS, Ghannoum O, Han Q, Hikosaka K, Jensen AM, Kelly JWG, Kruger EL, Mercado LM, Onoda Y, Reich PB, Rogers A, Slot M, Smith NG, Tarvainen L, Tissue DT, Togashi HF, Tribuzy ES, Uddling J, Vårhammar A, Wallin G, Warren JM, Way DA (2018) Acclimation and adaptation components of the temperature dependence of plant photosynthesis at the global scale. New Phytologist doi 10.1111/nph.15668. Colin Prentice reviewed this paper, and said: “This is a thorough and critical analysis, and a very clearly written account. While laying firmly to rest a number of common misinterpretations, it establishes important general patterns. I believe it will immediately become the definitive paper on photosynthetic temperature responses for some time to come.” It was no mean feat for a PhD student to lead this major multi-author effort! 

Yang JY, De Kauwe MG, Duursma RA, Medlyn BE (2018) Applying the concept of ecohydrological equilibrium to predict steady-state leaf area index. Journal of Advances in Modeling Earth Systems. doi 10.1029/2017MS001169. Vegetation models struggle to predict LAI in evergreen Australian ecosystems. Jim used the concept of ecohydrological equilibrium to successfully predict long-term mean LAI across Australia – also obtaining the stomatal operating point g1 into the bargain.  

Renchon AA, Griebel A, Williams CA, Medlyn BE, Duursma RA, Barton CVM, Maier C, Boer MM, Isaac P, Tissue DT, Resco de Dios V, Pendall E (2018) Upside-down fluxes Down Under: CO2 net sink in winter and net source in summer in a temperate evergreen broadleaf forest. Biogeosciences 15: 3703-3716. Alexis’ analysis of eddy covariance data at our local Cumberland Plains flux tower demonstrates that net C uptake is, remarkably, higher in winter than summer.  The effects of higher PAR in summer are outweighed by stomatal closure due to high VPD and increased soil respiration.  

Li XBlackman CJChoat B, Duursma RA, Rymer PD, Medlyn BE, Tissue DT (2018) Tree hydraulic traits are coordinated and strongly linked to climate-of-origin across a rainfall gradient. Plant, Cell & Environment doi: 10.1111/pce.13129 In a beautifully-executed experiment, Li demonstrates that stomatal closure and hydraulic failure co-vary in tree species spanning the NSW rainfall gradient. These data will help us predict the risk of future drought mortality in south-eastern Australia.  

Campany CE, Medlyn BE, Duursma RA (2017) Reduced growth due to belowground sink limitation is not fully explained by reduced photosynthesis. Tree Physiology, 37: 1042-1054  Modelling plant growth with a carbon balance model under source limitation is straightforward: growth is the outcome of photosynthesis and respiration. But what happens under sink limitation? Court’s novel experiment probes what happens to the C balance when plants are sink limited and provides important data for developing models that work under sink limitation.

Lu Y, Duursma RA, Medlyn BE (2016) Optimal stomatal behaviour under stochastic rainfall. Journal of Theoretical Biology 394:160-171.  Our group has previously studied the theory of optimal stomatal behaviour in depth, but only for non-water-stressed plants. Lu here solved the very non-trivial problem of optimal stomatal behaviour in a stochastic rainfall regime. Although the theory captures some features observed in nature, it also fails in some respects. Look out for Lu’s next paper, which generalizes the theory to include plant competition!

Ali AA, Medlyn BE, Aubier T, Crous KY, Reich PB (2015). Elevated carbon dioxide is predicted to promote coexistence among competing species in a trait-based model. Ecology & Evolution 5: 4717-4733. This paper of Ashehad’s is a classy marriage of process-based modeling with competition theory. The predictions that emerge deserve to be more widely known and tested by community ecologists.

Kelly JWG, Duursma RA, Atwell BA, Tissue DT, Medlyn BE (2015) Drought x CO2 interactions in trees: a test of the low-Ci mechanism. New Phytologist 209:1600-1612.  Jeff’s experiment was beautifully designed and executed to allow him to test and reject several long-standing hypotheses about the mechanisms underlying the drought x CO2 interaction. In particular, it demonstrates very nicely that leaf area adjustment is an important component of plant response to long-term drought stress.

Baig S, Medlyn BE, Mercado L, Zaehle S (2015) Does the growth response of woody plants to elevated CO2 increase with temperature? A model-oriented meta-analysis. Global Change Biology 21: 4303-4319.  Models predict that woody plants should respond more to rising CO2 at high temperature – but do they? Sofia carried out a meta-analysis of > 100 experiments on woody plants and found that the answer is .. we still can’t tell! The confidence intervals include both a positive interaction and no interaction. We need more experiments that are carefully designed to test this prediction – especially in the tropics. 

Zhou S, Medlyn BE, Sabaté S, Sperlich D, Prentice IC (2014) Short-term water stress impacts on stomatal, mesophyll, and biochemical limitations to photosynthesis differ consistently among tree species from contrasting climates. Tree Physiology 34: 1035-46.  Our models previously assumed that all species had similar drought sensitivity. Shuangxi carried out two phylogenetically controlled experiments using the Eucalyptus and Quercus genera to demonstrate that there is consistent variation in drought sensitivity that is related to the aridity of the species’ home climate – a major advance for our ability to model drought stress responses across ecosystems.

Spotlight on: Elevated CO2 Research

Medlyn BE, Zaehle S, De Kauwe MG, Walker AP, Dietze MC, Hanson P, Hickler T, Jain A, Luo Y, Partin W, Prentice IC, Thornton P, Wang S, Wang YP, Weng E, Iversen CM, McCarthy H, Warren J, Oren R, Norby R (2015) Using ecosystem experiments to improve vegetation models. Nature Climate Change 5: 528-534.  This paper is a short and readable summary of the Free-Air CO2 Enrichment Model-Data Synthesis, where we evaluated the assumptions in eleven ecosystem models against two ten-year forest FACE experiments. See also De Kauwe et al. (2013, 2014), Walker et al. (2014, 2015) and Zaehle et al. (2014). 

De Kauwe MG, Medlyn BE, Walker AP, Zaehle S, Asao A, Guenet B, Harper AB, Hickler T, Jain A, Luo Y, Lu X, Luus K, Parton WJ, Shu S, Wang Y-P, Werner C, Xia J, Pendall E, Morgan JA, Ryan EM, Carrillo Y, Dijkstra FA, Zelikova TJ, Norby RJ (2017) Challenging terrestrial biosphere models with data from the long-term multi-factor Prairie Heating and CO2 enrichment experiment. Global Change Biology, DOI: 10.1111/gcb.13643. In which we demonstrate that a suite of process-based ecosystem models are unable to simulate responses to CO2 and temperature in a prairie experiment, and probe the reasons why not. A set of critically important questions for modelling and experimental grassland research emerge.   

Medlyn BE, De Kauwe MG, Zaehle S, Walker AP, Duursma RA, Luus K, Mishurov M, Pak B, Smith B, Wang YPP, Yang XY, Crous KY, Drake JE, Gimeno TE, Macdonald CA, Norby RJ, Power SA, Tjoelker MG, Ellsworth DS (2016) Using models to guide field experiments: a priori predictions for the CO2 response of a nutrient- and water- limited native Eucalypt woodland. Global Change Biology 22:2834-2851. We applied our model intercomparison framework to the EucFACE experiment in advance of the experiment. The models predicted a wide range of possible outcomes in the experiment – highlighting the model uncertainties that measurements should be targeting. We strongly advocate this approach for any new large-scale experiment! 

Ellsworth DS, Anderson IC, Crous KY, Cooke J, Drake JE, Gherlanda AN, Gimeno TE, Macdonald CA, Medlyn BE, Powell JR, Tjoelker MG, Reich PB (2017) Elevated CO2 does not increase eucalypt forest aboveground productivity on a low-phosphorus soil. Nature Climate Change, doi:10.1038/nclimate3235. Results on above-ground productivity at EucFACE are in – and thus far, they support the models that incorporate phosphorus limitation. 

Spotlight on: Modelling Stomatal Behaviour

Medlyn BE, Duursma RA, Eamus D, Ellsworth DS, Prentice IC, Barton CVM, de Angelis P, Crous KY, Freeman M, Wingate L (2011) Reconciling the optimal and empirical approaches to modelling stomatal conductance. Global Change Biology 17: 2134-2144. Our now-classic paper that brings together the Ball-Berry-Leuning empirical stomatal models with the Cowan-Farquhar optimal stomatal theory. Please do not miss the corrigendum! 

Lin YS, Medlyn BE, Duursma RA, Prentice IC, Wang H, Baig S, Eamus D, Resco de Dios V, Mitchell P, Ellsworth DS, Op de Beeck M, Wallin G, Uddling J, Tarvainen L, Linderson M, Cernusak L, Nippert J, Ocheltree T, Tissue DT, Martin-StPaul N, Rogers A, Warren J, De Angelis P, Hikosaka K, Han Q, Onoda Y, Gimeno T, Barton CVM, Bennie J, Bonal D, Bosc A, Löw M, Macinnis-Ng C, Rey A, Rowland L, Setterfield S, Tausz-Posch S, Zaragoza-Castells J, Broadmeadow M, Drake J, Freeman M, Ghannoum O, Hutley L, Kelly J, Kikuzawa K, Kolari P, Koyama K, Limousin J-M, Meir P, Costa A, Mikkelsen T, Salinas N, Sun W, Wingate L (2015) Optimal stomatal behaviour around the world. Nature Climate Change 5: 459–464. We put together leaf gas exchange data from ecosystems all around the world to test the predictions of our optimal stomatal conductance model (Medlyn et al. 2011). We concluded that “Plants use water wisely – mostly”

De Kauwe MG, Kala J, Lin Y-S, Pitman AJ, Medlyn BE, Duursma RA, Abramowitz G, Wang YP, Miralles D (2015). A test of an optimal stomatal conductance scheme within the CABLE Land Surface Model. Geoscientific Model Development 8: 431-452. We implemented our new optimal stomatal model, based on theory (Medlyn et al. 2011) and a large empirical dataset (Lin et al. 2015) into the CABLE Land Surface Model. Short story – it works! 

Kala J, De Kauwe MG, Pitman AJ, Medlyn BE, Wang Y-P, Lorenz R, Perkins-Kirkpatrick S (2016) Impact of the representation of stomatal conductance on model projections of heatwave intensity. Nature Scientific Reports 6: art 23418. The new representation of stomatal conductance that we proposed has important implications for climate – in particular, development of heatwaves. 

Medlyn BE, De Kauwe MG, Lin Y-S, Knauer J, Duursma RA, Williams CA, Arneth A, Clement R, Isaac P, Limousin J-M, Linderson M-L, Meir P, Martin-StPaul N, Wingate L (2017) How do leaf and ecosystem measures of water-use efficiency compare? New Phytologist, doi:10.1111/nph.14626. We identify an important problem for model calibration and validation: global datasets of water-use efficiency obtained using different methods show different patterns across plant functional types. New research is required urgently to reconcile these discrepancies. 

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