(CArbon NItrogen Forest Labelling EXperiments)
The cycles of carbon and nitrogen interact in many and complex ways in forest ecosystems. Carbon dioxide is fixed in photosynthesis catalyzed by the enzyme Rubisco, often the major N compound in plant leaves. The sugars produced are used for building plant organs and to sustain their metabolism; a fraction of the C is used to produce and sustain roots and their mycorrhizal fungal symbionts, which are essential in the uptake of N from the soil. During decomposition of plant material in the soil, C is decoupled from N and CO₂ is released back to the atmosphere. These are only a few examples of the many vital interactions in forests between the cycles of C and N. However, much of the important details of these interactions are poorly known, restricting our ability to predict their outcome in a changing environment. Very detailed studies have been conducted of micro- or mesocosms, studying microorganisms and/or very small plants. Such studies have revealed important insights, but their results cannot safely be extrapolated quantitatively to the greater complexity and vastly different scales in the field.

We decided to overcome the technical difficulties of following molecules and atoms of C and N directly in the field. The basic technique, so called pulse-chase experiments in which isotopically labelled C or N is added to the ecosystem and then followed had been applied successfully at smaller scales. In the CANIFLEX project we use comparatively large (50 m²) plots, short labelling periods and stable (non-radioactive) isotopes of C and N. Because ¹²C and ¹⁴N are the most common stable isotopes of C and N in nature, we add ¹³C to the plants and ¹⁵N to the soil. The major focus is on the ¹³C labelling, which involves letting the forest take up ¹³CO₂ through photosynthesis. Using highly labelled ¹³CO₂ in temporary plastic (200-250 m³) chambers a few hours of labelling is enough to produce traceable quantities of ¹³C in many compartments of the forest ecosystem, including forest microorganisms. We study seasonal aspects of C allocation from the tree canopy to the belowground system and how additions of N alter the allocation of C and the cycling of C. In 2007 we labelled 8 plots, which were all re-labelled in 2008.

In 2010, we labelled separately only the understory plants in a pine forest, which consists of ericaceous species. 

The core science team is Peter Högberg, Torgny Näsholm, Vaughan Hurry, Sune Linder, Tomas Lundmark, Ross McMurtrie, Mona N. Högberg, Sonja Keel, Daniel Metcalfe, Catherine Campbell and Niles Hasselquist.

Current and previous collaborators are Sabine Göttlicher, Nick Betson, Tord Magnusson, Andreas Schindlbacher, Phil Ineson, Jens-Arne Subke, Harry Vallack, Andreas Richter, Barry Thornton, Andy Midwood, Elizabeth Powers, Juergen Schleucher and Maria Briones.

Current and previous members of the technical team: Jan Parsby, Thomas Hörnlund, Mark Blackburn, Stephan Schaffner, Abdulmajid Mahomoud, Per-Erik Wikberg, Axel Högberg, Jonathan Bryntesson and John Högberg.