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Towards a better understanding of carbon flux

In March 1999, a ca. 45 m tall construction crane was installed in a highly diverse, mature temperate forest near the village of Hofstetten, south of Basel (Swiss Canopy Crane project, Switzerland). The crane provides access to the canopy using a gondola for in situ research. With a new type of FACE technique (Free Air CO2 Enrichment), selected trees have been exposed for several years to a COz - enriched atmosphere (540 ppm), simulating the expected ambient concentration of ca. 2060. Using the results of the Swiss Canopy Crane project (photosynthesis and tree growth under elevated carbon dioxide) and with regard to typical students' conceptions about the carbon cycle, we developed a teaching strategy to clarify the flux of carbon in trees. Our teaching unit draws attention to processes such as root and soil respiration (e.g. respiration by soil animals), which are central to understanding carbon fluxes but are rarely presented in textbooks. The findings of this study are relevant and very topical because they help students to understand the consequences of rising levels of atmospheric carbon dioxide for carbon flux in plants.