Where is the carbon going?

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.

How to apply

Applications need to be submitted via the University of Birmingham postgraduate portal by midnight on 11.01.2021. Please first check whether the primary supervisor is within Geography, Earth and Environmental Sciences, or in Biosciences, and click on the corresponding PhD program on the application page.

This application should include

• a brief cover letter, CV, and the contact details for at least two referees

• a CENTA application form

• the supervisor and title of the project you are applying for under the Research Information section of the application form.

Referee’s will be invited to submit their references once you submit your application, but we strongly encourage applicants to ensure referees are aware of your submission and expecting a reference request from us. Students are also encouraged to visit and explore the additional information available on the CENTA website.