Afforestation is seen as a major contributor to meeting the Paris Agreement carbon (C) targets. However, the potential for C uptake, and thus the potential climate mitigation capacity of forests has been severely overestimated by global circulation models not accounting for nutrient limitation. Many micro- and macro-nutrients can constrain gross primary production (GPP), but at the global scale it is widely accepted that nitrogen (N) and phosphorus (P) limitation have the prominent role. Nitrogen & P cycles interact strongly with biogeochemical processes, and synergistic interactions between multiple limiting resources (i.e. co-limitation) are common. Understanding how nutrient availability and uptake is mediated by plant-soil-microbe feedbacks is paramount to accurately modelling the C balance of forest ecosystems in future climates. In temperate forests, mycorrhizal fungi and bacteria mediate plant interactions within the soil that include the mineralisation of organic matter and uptake of nutrients released during the mineralization. As atmospheric CO2 concentrations continue to increase, the carboxylation efficiency of Rubisco improves resulting in a fertilization effect on plant growth until constrained by the availability of other resources, such as N and P. Therefore, understanding the growth response of forests to soil N and P availability and the impact of fertilization is an important aspect of forest ecology required to support future forest management policy for climate mitigation.
This PhD project aims to improve our understanding of nutrient cycling and forest productivity by investigating how soil nutrient availability and root uptake preferences for different nutrient forms in response to N and P availability changes, and to unravel how mycorrhizal fungi trade nutrients and carbohydrate with trees in supporting their growth. Predicting the response of forest ecosystems to climate change will only be possible when we fully understand the processes that govern nutrient availability.
Methodology:
This research will utilize a fully factorial (n=3) N and P nutrient addition experiment with a 160-year-old Quercus robur forest located at the Birmingham Institute of Forest Research (BIFoR), aligned with the 5-year NERC QUINTUS project, that will facilitate the investigation of N and P co-limitation and its constraints on forest productivity. Experimental work will include N and P mineralization rates as influenced by fertilization and the underlying soil-plant-microbe interactions, followed by the measurement of root uptake preferences for different nutrient forms as well as tree growth responses. In situ monitoring of nutrients will be carried out using assays in microfluidic devices and portable read-out instrumentation. Mycorrhizal fungi community structure and abundance will be evaluated to understand symbiotic trade-off between the species involved under scenarios of nutrient limitation and enrichment. The indices of these plant-microbe interactions and nutrient cycling will also involve laboratory work at Birmingham and Bangor Universities.
Training and skills:
Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.
The student will benefit from supervision across three UK research institutes. The student will be based at the University of Birmingham where a range of analytical training is available. Specific analytical training will be provided in the operation of instruments nutrient analysis, isotope tracing for N and P (Birmingham and Bangor) and mycorrhizal community structure to determine functional groups and their relationship to soil nutrient status and tree growth responses (Bangor). Training and lab experiments at Bangor and UKCEH will open up new avenues for collaborative research training. Equally, the student will spend time in the School of Chemistry at Birmingham to learn novel analytical methods, microfluidics, and instrumentation.
Partners and collaboration (including CASE):
This studentship benefits from access to the only global temperate forests Free Air Carbon Dioxide Enrichment (FACE) facility and infrastructure (>£20million) (https://www.birmingham.ac.uk/research/bifor/face/index.aspx) and the Forest Ecology and Biogoechemistry Laboratory Facilities at Bangor University and UKCEH-Bangor). This studentship will benefit from the high experimental costs of these projects and facilities, which is beyond the funding capacity of any single PhD studentship. The involvement of UKCEH and Bangor University offers significant values in terms of access to facilities. Access to mycorrhizal functionality characterization facilities at Bangor University (>£170k), and an internship at UKCEH will thus support this studentship.
Possible timeline:
Year 1:
- Literature review and training in analytical instruments (chromatography, colorimetry, isotopes), microfluidics, and experimental design at Birmingham, Bangor University and UKCEH-Bangor. Introductory visits to the BIFoR-FACE in England.
- Training in the School of Chemistry (6 weeks) on microfluidic devices.
- Placement (8 weeks) at Bangor University to learn about forest soil microbial and fungal ecology techniques and the use of radioisotopes in mesocosms.
- Research plan finalisation including statistical design, installation of root boxes for root uptake preferences, setting up decomposition and nutrient availability trial and publication of a literature review paper.
Year 2:
- Monthly measurement of available nutrients in experimental plots, net N mineralization rates and mycorrhizal trade-offs with roots in terms of nutrient and carbon exchanges.
- Develop colorimetric assays in microfluidic devices for detection of selected anions and cations.
- Functional genetic markers for N and P uptake and mineralisation will be determined in rhizosphere soils.
- Application of stable- and radioisotope tracers for quantifying relative availability of N and P in soils to roots under N & P addition treatments and how such changes affect root uptake preferences.
- Tree NPP measurements (leaf, stem, root and hyphae) in mesoscosms and field trials.
- Data analysis and compilation of results for publication.
Year 3:
- Continuation of nutrient mineralization, availability and root uptake preferences for different N forms.
- Obtain and compare data obtained using well-established laboratory methods and microfluidic devices with portable read-out instrumentation.
- Changes in root carbon allocation to mycorrhizae in response of nutrient availability (Bangor University) and changes in decomposition rates (University of Birmingham).
- Data analysis and completion of experimental work.
Year 4:
- Thesis write up, defence and publications.
- Wider involvement with supervisor linked project partners offering further opportunities for pooling data within a multidisciplinary data pool potentially feeding into large synthesis papers and methodologies.
Please email potential supervisor Dr Ullah ([Email Address Removed]) for more information.
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