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

Project Highlights:

·        Unravelling the effect of CO₂ fumigation of a mature forests, looking both below and above ground processes

·        Research at BiFoR FACE- the only CO₂ experiment in mature temperate forests

·        Work with a world-leading team on global change, ecology and biogeochemistry.

Overview:

National pledges to reduce greenhouse gas emissions and limit global warming to 1.5 °C depend on the balance between carbon (C) emissions and sequestration. Globally, terrestrial vegetation acts as a large carbon sink, absorbing around one third of anthropogenic CO₂ emissions. Trees are a fundamental component to this equation, absorbing CO₂ during photosynthesis and allocating this C into their leaves, wood and roots. Trees also export large amounts of C as root exudates and into mycorrhizae, to maintain their supply of water and nutrients. Whilst much of this carbon returns to the atmosphere on short timescales, part of it remains within biomass and soil for decades or centuries.

Whether forests will continue to contribute to the global carbon sink under elevated CO₂ concentrations (eCO₂) is still uncertain. Trees grow faster under eCO₂, but tree growth cannot increase indefinitely, partially because growth will be limited by other factors, such as nutrient availability. To an extent, trees can compensate that by allocating the extra C belowground, increasing root growth, exudation and mycorrhizal activity to explore the soil and obtain more nutrients and water. Experiments in which plants are exposed to eCO₂ have shown greater C capture, notably by increasing root growth. However, most of our knowledge is based on experiments using seedlings or relatively young forests. There is much less evidence for eCO₂ responses in mature trees, but an Australian experiment has shown that eCO₂ enrichment does not result in more ecosystem-level C sequestration in a mature forest.

Understanding where the trees will allocate extra C under eCO₂is crucial to understand the future of the global C sink. As with many underground processes, allocation to fine roots is particularly uncertain. This project makes use of the BIFoR FACE experiment, the only eCO₂ experiment in a mature temperate forest in the world, to investigate above and below-ground C allocation, providing evidence for a crucial aspect of the response of forest ecosystems to eCO₂.

Methodology:

This project will take place at the Free Air CO₂ Enhanced (FACE) experiment as part of the Birmingham Institute of Forest Research (BIFoR). BIFoR FACE is one of the only FACE sites in the world. It exposes a 100-years old oak forest to elevated CO₂ at around 550ppm, which is what we expect to reach by 2050. Thanks to this unique facility you will be able to investigate the influence of elevated CO₂ on trees carbon allocation, including leaf and root productivity.

You will collect and images using cutting-edge minirhizotron techniques. These images will be vectored and converted into root production, which will be used to compare control and experiment plots, investigating the influence of eCO₂ on root production. Additionally, you will analyse data on leaf area collected in the previous years of the experiment aiming to understand the effect of eCO₂ on carbon allocation.

Training and skills:

You will be trained to use state-of-the-art minirhizotron techniques, using a camera system specially designed to investigate underground dynamics with little disturbance to the soil. You will be working with a large amount of data and will receive training on statistical techniques and programming using the R language. You will present your work at high profile conferences including at least one international conference, to sharpen your communication skills and develop your network. You will also be among the very active BIFoR community, allowing you to discuss your work with scientists from all over the world.