The response of terrestrial ecosystems to rising atmospheric CO2 concentration (Ca), particularly under nutrient-limited conditions, is a major uncertainty in Earth System models. The Eucalyptus Free-Air CO2 Enrichment (EucFACE) experiment, recently established in a nutrient- and water-limited woodland presents a unique opportunity to address this uncertainty, but can best do so if key model uncertainties have been identified in advance. We applied seven vegetation models, which have previously been comprehensively assessed against earlier forest FACE experiments, to simulate a priori possible outcomes from EucFACE. Our goals were to provide quantitative projections against which to evaluate data as they are collected, and to identify key measurements that should be made in the experiment to allow discrimination among alternative model assumptions in a postexperiment model intercomparison. Simulated responses of annual net primary productivity (NPP) to elevated Ca ranged from 0.5 to 25% across models. The simulated reduction of NPP during a low-rainfall year also varied widely, from 24 to 70%. Key processes where assumptions caused disagreement among models included nutrient limitations to growth; feedbacks to nutrient uptake; autotrophic respiration; and the impact of low soil moisture availability on plant processes. Knowledge of the causes of variation among models is now guiding data collection in the experiment, with the expectation that the experimental data can optimally inform future model improvements.
Bibliographical noteFunding Information:
The National Climate Change Adaptation Research Facility (NCCARF), Primary Industries Adaptation Research Network (PIARN) supported this project and travel for the participants to Sydney, Australia. Additional support via EucFACE as an initiative supported by the Australian Government through the Education Investment Fund and the Department of Industry and Science, in partnership with the University of Western Sydney, is acknowledged. Research support from the Australian Research Council is also acknowledged. Contributions from APW, XJY, MDK, KL and RJN were supported by the US Department of Energy (DOE) Office of Science's Biological and Environmental Research (BER). The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7 2007-2013) under grant agreement n? 238366 (Greencycles II). This study is a contribution to MERGE, a strategic research area of Lund University.
© 2016 John Wiley & Sons Ltd
- carbon dioxide
- ecosystem model
- Eucalyptus tereticornis