Beyond global change – lessons from 25 years of CO2 research

Background/Question/Methods

Over the past 25 years, countless experiments on the impact of increased atmospheric CO₂ concentration on various plants and ecosystems have been conducted. While this research was motivated to better understand and predict how rising CO₂ will affect the structure and function of ecosystems in the future, it also shed light on some general, CO₂-research independent, aspects in ecological research. Interestingly, it is these general aspects that often created confusion and led to misinterpretation of data in the past, and is continuing to do so. Here, we focus on seven key issues emerging from many years of CO₂-research: (1) the confusion between fluxes and pools, (2) the stoichiometric aspects of growth and biomass production, (3) resource allocation, (4) data scaling and the choice of a reference metric, (5) the issue of time and timing (experimental duration, ontogenetic shifts), (6) confounding and second-order effects, and (7) the key role of biodiversity. 

Results/Conclusions

We find that the derived principles are strongly related among each other and their concurrent consideration requires experimenters and modellers likewise to maintain a broad, holistic perspective. Taken appropriately into account, these principles can be very powerful in assessing the validity, plausibility and generality of experimental and modelling results. We conclude that neglecting to adequately address these key issues in ecological research may lead to overestimations of measured responses and/or simplistic interpretations. Our examples originate mostly from research on plant responses to elevated atmospheric CO₂, but are also applicable to other areas of ecological research. We provide a checklist that can serve both the planning and the interpretation of ecological field experiments and may help to avoid common pitfalls.