|The CANIFLEX Project|
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.
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.
The CANIFLEX experiments have received generous funding from the Kempe Foundations (8.5 million SEK), the Swedish Science Council (VR) and the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS).
Vallack HW, Leronni V, Metcalfe DB, Högberg P, Ineson P, Subke J-A 2011 Application of nitrogen fertilizer to a boreal pine forest has a negative impact on the respiration of ectomycorrhizal hyphae. Plant and Soil, accepted.
Högberg P, Högberg MN, Göttlicher SG, Betson NR, Keel SG, Metcalfe DB, Campbell C, Schindlbacher A, Hurry V, Lundmark T, Linder S & Näsholm T 2008 High temporal resolution tracing of photosynthate carbon from the tree canopy to forest soil microorganisms. New Phytologist 177, 220-228.
Subke J-A, Vallack HW, Magnusson T, Keel SG, Metcalfe DB, Högberg P & Ineson P 2009 Short term dynamics of abiotic and biotic soil 13CO2 effluxes after in situ 13CO2 pulse labelling of boreal pine forest. New Phytologist, 183, 349-357.
Högberg MN, Briones MJI, Keel SG, Metcalfe DB, Campbell C, Midwood AJ, Thornton B, Hurry V, Linder S, Näsholm T & Högberg P 2010 Quantification of effects of season and nitrogen supply on tree belowground carbon transfer to ectomycorrhizal fungi and other soil organisms in a boreal pine forest. New Phytologist, 187, 485-493.