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The impact of nitrogen on the fate of recently assimilated carbon in forest soils

Final Report Summary - NITFOR (The impact of nitrogen on the fate of recently assimilated carbon in forest soils)

Global climate change is strongly linked to the accumulation of greenhouse gases in the atmosphere. In particular, CO2 contributes almost 45 - 60 % to the observed anthopogenic global warming yet has the potential to be captured by trees and stored either in woody biomass or in soils over long time periods. Consequently, the Kyoto protocol recommends afforestation as one viable option to help reduce atmospheric CO2 concentrations. While the above-ground carbon cycle is well constrained, there remain great uncertainties in below-ground carbon cycling. For example, it is currently not known what proportion of carbon, fixed by trees in photosynthesis as CO2, is stored in soil, released back to the atmosphere as CO2. We proposed to tackle specific key questions about the fate of carbon in forests by taking advantage of existing afforestation experiments in England (main phase) and in Russian Siberia (return phase), by combining new stable isotopes methods and innovative in-growth core approaches.

The major objective for the return phase was to determine the Siberian tree species effects on the amount and timing of C transfer through roots to myccorhiza. We studied the C transport to mycorrhiza under six most commonly dominant in boreal forests tree species using the Siberian afforestation experiment. The CO2 flux from mycorrhizal and non-mycorrhizal mesh collars was measured every two weeks from May until October in 2011. During the overall dry summer of 2011, the difference in soil surface CO2 flux between the tree species were determined mostly by difference in mycorrhizal flux. The mycorrhizal CO2 flux was not linked to soil temperature but rather to trees phenology and to photosynthetic activity. All tree species transferred more carbon to mycorrhiza during the second half of summer and in September; this is because all the carbon photosynthesised earlier is used for building the trees biomass. Seasonal variation in C transfer to mycorrhiza was much larger than hourly variation (within a day). Tree species strongly differed in C flux to mycorrhiza: more C was transferred by deciduous species than by conifers.

Overall, the project:

1) greatly advanced our knowledge of belowground C cycling in forest ecosystems and
2) established a new cooperative link between researchers of the Institute of Forest in Krasnoyarsk and the University of York.

As a result of the return phase, Dr Oleg Menyailo is fully integrated into the research community in Krasnoyarsk, he is a researcher at the Institute of Forest and a Professor at the Siberian Federal University. Three papers are published in peer-reviewed journals Soil Biology and Biochemistry, Eurasian Journal of Soil Science and Russia Germany Humboldt Journal, and at least two papers are planned for Global Change Biology and New Phytologist.