Impact of CO2 rise on root, leaf and wood production: The future of tree C allocation

Globally, trees absorb CO2 in photosynthesis and allocate carbon into leaves, wood, and roots where it can then remain within biomass and soil for decades. Therefore, carbon uptake by terrestrial vegetation is a vital player in the global carbon sink, absorbing around 1/3 of anthropogenic CO2 emissions. The question remains however, whether, and to what extent, forests will continue to contribute to the global carbon sink under elevated CO2 concentrations.

Research suggests that trees can carry out increased levels of photosynthesis under elevated CO2, but growth cannot increase indefinitely due to other limiting factors such as nutrient availability. Trees may be able to combat this to an extent by allocating this extra carbon belowground by increasing root growth, exudation, and microbial activity to explore the soil and obtain more nutrients and water.

This project aims to unravel the effect of CO2 fumigation, focussing on belowground processes of mature forests. Previous studies which have found greater carbon capture, notably by increasing root growth, have often been focussed on younger forests and plantations; so-called 'first generation' FACE (Free Air Carbon Enrichment) facilities, and do not necessarily produce an accurate representation of the impact of elevated CO2 on mature forests.

This project will be carried out at the Birmingham Institute of Forestry Research (BIFoR), only the second running 'second generation' FACE facility in the world in collaboration with Forest Research and the Met Office.

Root production will be measured through the collection of images using a minirhizotron camera, a cutting edge, non-destructive root investigation technique, which will then be vectored and converted to rates of root production. This methodology will be used alongside more traditional methods of root extraction and examination using soil cores. Data on root production will then be considered alongside other relevant carbon storage data collected in the previous years of the BIFoR experiment, such as leaf area, to further understand where trees will allocate extra carbon under elevated CO2 and provide vital information to understand the future of the global carbon sink.