Analysis of elemental ratios (stoichiometry) in food webs may provide fundamental information on the uptake, allocation and sequestration of carbon (C) and key nutrient minerals like phosphorus (P) and nitrogen (N) from the cellular level to ecosystems. In sum, these processes will also play a major role for the global cycling of these elements. The relative abundance of key nutrient minerals like phosphorus (P) and nitrogen (N) is not only instrumental to primary production, also secondary production (grazers) may be directly limited by the relative abundance of P and N. And when C:N or C:P ratios are high in primary producers, an increasing share of C will be in excess, relative to the grazers’ demands. This will have implications not only for energy transfer in food webs, but also community composition and system stability. It will also be a major determinant of CO₂-uptake at the base of the food-web to yield at the top.

The project has consisted of 22 scientists who have analyzed these aspects in cells and ecosystems, covering topics from the role of P for cellular RNA and growth rate to large-scale ecosystem analysis and models. The work has addressed from three points of departure: continued work with existing data, projects and publication, analysis of large datasets from various databases and theoretical works and models.

The year has resulted in a number of papers in top-ranking journals including Nature, Science, American Naturalist, Ecology and Ecology Letters. It has also sparked off new research ideas and new research application. Our group has also initiated a continuing development within this developing branch of biology, and thus the full output of this year in the form of ideas, concepts and papers will continue for several more years.

The group has worked with aspects from the molecular scale up to ecosystems. Perhaps the most important output from the group at the “big scale” end was the discovery, based on a huge database of thousands of marine and freshwater data worldwide, that elemental proportions (carbon:nitrogen:phosphorus, C:N:P – the widely used Redfield ratio) in lakes and oceans differ substantially from what had been previously assumed. More specifically, biological material in lakes and oceans is far richer in C than previously assumed (e.g. the atomic C:P-ratio is 133 rather than 116), hence substantially more C may be sequestered per mole of P or N. This has wide implications for several ecological processes, but most important is that it will have strong impact on the calculations of the global carbon cycle, where Redfield ratio and oceans play a major role. Models of long-term fluctuations in global oxygen and CO₂ concentrations build, to a large extent, on the Redfield ratio, and the new data emerging from our group will play an important role for largescale biogeochemical models. The work has been submitted to Nature.

Another major achievement has been to test stoichiometric and ecological effects of the strong increase on increased anthropogenic N-deposition. Norwegian data is particularly suitable in this regard, owing to the very strong gradient in N-deposition from south to north, where the south is heavily influenced by anthropogenic N-deposition originating mostly from continental Europe, while the north represents pristine conditions. N-deposition data was merged with the large lake database and statistical analysis demonstrated a major impact of N-deposition on N:P-ratios of the lakes and trophic structure. These findings are intriguing since they demonstrate a potentially strong coupling from the global disturbance in the N-cycle via effects on elemental ratios to ecosystem effects. Also this paper is scheduled for Nature.

To summarize, our group at CAS has been highly successful, not only in terms of producing papers, but also in establishing networks and pointing to future prospects and directions for this emerging field.