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The response of trees to CO2 and climate inferred from new tree ring isotopes approaches


Key facts

Type of research degree
Application deadline
Ongoing deadline
Project start date
Sunday 1 October 2023
Country eligibility
UK only
Source of funding
Professor Roel Brienen and Professor Emanuel Gloor
Additional supervisors
Prof. Bruce Turnbull (School of Chemistry), Dr. Arnoud Boom (University of Leicester)
<h2 class="heading hide-accessible">Summary</h2>

Are you passionate about trees and climate change? Are you interested in solving important and relevant questions regarding forest responses to global change? Do you want to perform cutting edge isotope and tree ring work? Then please apply for this fully funded PhD to work in a dynamic, cross-disciplinary team on the Leverhulme funded research project &ldquo;Unlocking the full potential of tree ring oxygen isotope archives&rdquo;.

<h2 class="heading hide-accessible">Full description</h2>

<p style="text-indent:36.0pt; margin-bottom:11px">Both increases in atmospheric CO2 and the resulting climatic changes (e.g. warming) are affecting forests globally (Walker et al. 2020). Atmospheric CO2 increases reduce CO2 limitation of trees&rsquo; photosynthesis, possibly leading trees to downregulate stomatal conductance and thereby transpiration rates (Frank et al. 2015, Adams et al. 2020). The warming of the Earth surface affects tree functioning directly and indirectly through changes the Earth&rsquo;s hydrological cycle (i.e. increasing intensity and frequency of droughts and floods). Our understanding how forests respond to these complex drivers remains incomplete, but is important as we depend on forests for maintaining biodiversity, clean water and air, and as forests are large carbon stores.</p> <p>&nbsp;</p> <p>An important approach towards gaining insight in tree responses to global change is the use of tree rings and isotopes. Carbon isotope variation in tree rings provide indications of changes in plant water use efficiency, while oxygen isotopes provide a mixed signal of the plant source water and plant physiological changes to their environment. In theory, the combined use of the two isotopes in tree rings therefore potentially allows disentangling climate from tree physiology responses (Scheidegger et al. 2000), but current methods are limited as oxygen isotopes provide a mix of signals from the plant water source and plant physiology (primarily leaf level processes) (Lin et al. 2022). To make full use of these approaches we require new developments to enable to separate these signals (Sternberg 2009). In this project you will help developing and testing novel multi-proxy tree ring isotope approaches to assess the responses of trees to CO2 and climate. This will be done through working in a multidisciplinary team consisting of biochemists, Earth scientists, ecophysiologists, and isotope specialists.</p> <p>&nbsp;</p> <p>You will apply new chemical techniques to tree ring samples to separate oxygen isotope signals originating from the source water from those related to tree physiology and test these approaches on a range of sites and species. For this test you will make use of existing samples and complement these with new field collections from a number of sites, including possibly tropical trees. For a select set of species you will then develop long tree ring isotope chronologies to assess the long-term response to climate and CO2. This research is expected to provide new insights in plant ecophysiological responses, and improve the interpretation of oxygen isotopes from tree rings for palaeoclimate studies.</p> <p>&nbsp;</p> <p>Adams, M. A., T. N. Buckley, and T.L. Turnbull. 2020. Diminishing CO2-driven gains in water-use efficiency of global forests. Nature climate change 10:466-471.</p> <p>Frank, D. C., et al. 2015. Water-use efficiency and transpiration across European forests during the Anthropocene. Nature climate change 5:579-583.</p> <p>&nbsp;</p> <p>Scheidegger, Y. et al. 2000. Linking stable oxygen and carbon isotopes with stomatal conductance and photosynthetic capacity: a conceptual model. Oecologia 125:350-357.</p> <p>&nbsp;</p> <p>Sternberg, L. 2009. Oxygen stable isotope ratios of tree-ring cellulose: the next phase of understanding. New Phytologist 181:553-562.</p> <p>Lin, W., M. M. Barbour, and X. Song. 2022. Do changes in tree?ring &delta;18O indicate changes in stomatal conductance? New Phytologist 236:803-808.</p> <p>Walker, A.P.,&nbsp; et al. 2021. Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO2.&nbsp;New phytologist,&nbsp;229(5), pp.2413-2445.</p> <p style="margin-bottom:11px">&nbsp;</p> <p style="margin-bottom:11px">Information about the Award</p> <ul> <li>We are offering 1 full-time PHD scholarship in the School of Geography for one UK candidate, covering a matching UKRI maintenance stipend (currently &pound;17,668 in 2022/23) and UK&nbsp;tuition fees for three and a half years, subject to satisfactory progress.&nbsp;</li> </ul> <p>&nbsp;</p> <p>Duration of the Award</p> <ul> <li>Full-time (3.5 years). The award will be made for one year in the first instance and renewable for a further period of up to two and a half years, subject to satisfactory academic progress.</li> </ul> <p>&nbsp;</p> <p>Other Conditions</p> <ul> <li>Applicants must not have already been awarded or be currently studying for a doctoral degree.</li> <li>Awards must be taken up preferably by 1st&nbsp;October 2023, or the earliest date afterwards.</li> <li>Applicants must live within a reasonable distance of the University of Leeds whilst in receipt of this scholarship.</li> </ul>

<h2 class="heading">How to apply</h2>

<p class="MsoNoSpacing">Apply for a research place of study, through the&nbsp;<a href="">online application form.</a>&nbsp;</p> <h4 class="MsoNoSpacing">If English is not your first language, you must provide evidence that you meet the University&#39;s minimum English language requirements (below).</h4> <p>Applications will be considered on an ongoing basis. &nbsp;Potential applicants are strongly encouraged to contact the supervisors for an informal discussion before making a formal application. &nbsp;We also advise that you apply at the earliest opportunity as the application and selection process may close early, should we receive a sufficient number of applications or that a suitable candidate is appointed.</p> <p><em>As an international research-intensive university, we welcome students from all walks of life and from across the world. We foster an inclusive environment where all can flourish and prosper, and we are proud of our strong commitment to student education. Across all Faculties we are dedicated to diversifying our community and we welcome the unique contributions that individuals can bring, and particularly encourage applications from, but not limited to Black, Asian, people who belong to a minority ethnic community, people who identify as LGBT+ and people with disabilities. Applicants will always be selected based on merit and ability.</em></p> <p>&nbsp;</p>

<h2 class="heading heading--sm">Entry requirements</h2>

Applicants to this scholarship should normally have:<br /> <br /> &bull; strong interest in environmental and earth system science and global change<br /> &bull; a good honours degree or a Masters degree (or equivalent experience) in disciplines such as Physical Geography, Physical Sciences, Mathematics, Environmental sciences, Biology or a related subject<br /> &bull; strong analytical and numerical skills<br /> <br /> Applicants to research degree programmes should normally have at least a first class or an upper second class British Bachelors Honours degree (or equivalent) in an appropriate discipline. The criteria for entry for some research degrees may be higher, for example, several faculties, also require a Masters degree. Applicants are advised to check with the relevant School prior to making an application. Applicants who are uncertain about the requirements for a particular research degree are advised to contact the School or Graduate School prior to making an application.<br /> <br /> Applicants who are uncertain about the requirements for a particular research degree are advised to contact the Faculty of Environment prior to making an application.<br /> <br /> <br />

<h2 class="heading heading--sm">English language requirements</h2>

The minimum English language entry requirement for research postgraduate research study is an IELTS of 6.0 overall with at least 5.5 in each component (reading, writing, listening and speaking) or equivalent. The test must be dated within two years of the start date of the course in order to be valid. Some schools and faculties have a higher requirement.<br /> <br />

<h2 class="heading">Funding on offer</h2>

<p style="margin-bottom:11px">We are offering 1 full-time PHD scholarship in the School of Geography for one UK candidate, covering a matching UKRI maintenance stipend (currently &pound;17,668 in 2022/23) and UK&nbsp;tuition fees for three and a half years, subject to satisfactory progress.&nbsp;</p> <p style="margin-bottom:11px">&nbsp;</p> <p style="margin-bottom:11px">&nbsp;</p>

<h2 class="heading">Contact details</h2>

<p>For further information please contact the Faculty of Environment:;<br /> Contact both supervisors for informal enquiries: Roel Brienen ( and Emanuel Gloor (;</p>