Biogeosciences, 15, 4003–4018, 2018 https://doi.org/10.5194/bg-15-4003-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. Inferring the effects of sink strength on plant carbon balance processes from experimental measurements Kashif Mahmud1, Belinda E. Medlyn1, Remko A. Duursma1, Courtney Campany1,2, and Martin G. De Kauwe3 1Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, Australia 2Department of Biology, Colgate University, NY 13346, USA 3ARC Centre of Excellence for Climate Extremes, University of New South Wales, Sydney, NSW 2052, Australia Correspondence: Kashif Mahmud (
[email protected]) Received: 21 February 2018 – Discussion started: 26 February 2018 Revised: 13 June 2018 – Accepted: 15 June 2018 – Published: 3 July 2018 Abstract. The lack of correlation between photosynthe- 1 Introduction sis and plant growth under sink-limited conditions is a long-standing puzzle in plant ecophysiology that currently Almost all mechanistic models of terrestrial vegetation func- severely compromises our models of vegetation responses to tion are based on the carbon (C) balance: plant growth is rep- global change. To address this puzzle, we applied data assim- resented as the difference between C uptake (through pho- ilation to an experiment in which the sink strength of Euca- tosynthesis) and C loss (through respiration and turnover of lyptus tereticornis seedlings was manipulated by restricting plant parts). This approach to modeling plant growth dates root volume. Our goals were to infer which processes were back to early crop and forest production models (McMurtrie affected by sink limitation and to attribute the overall reduc- and Wolf, 1983; de Wit and van Keulen, 1987; de Wit, 1978) tion in growth observed in the experiment to the effects on and now provides the fundamental quantitative framework various carbon (C) component processes.