PhD Research Project: CENTA NERC - Old growth, new carbon: The aboveground carbon-allocation respon

The response of forest ecosystems to elevated CO2 is one of the major uncertainties in understanding the impact of increased CO2 emissions1. A key feedback system exists between terrestrial ecosystems and atmospheric CO2: increasing CO2 may stimulate photosynthesis, in turn increasing ecosystem carbon sink capacity and therefore slowing the rate of CO2 increase. This carbon-climate feedback is crucial to future climate projections, but still is the most uncertain. Temperate forests are particularly important biomes for controlling this feedback.
The fundamental photosynthetic behaviour is understood, as is much of the behaviour of saplings in laboratory media and plantations of immature trees on arable soil. The behaviour of mature trees in forest soil systems is not well established, because the experiments required are of a magnitude very seldom seen in terrestrial ecology (Figure 1).
Free-Air Carbon Dioxide Enrichment (FACE) facilities are the most direct and robust platform to study the effects of elevated CO2 on woodland/forest ecosystems2. Experiments currently underway include EucFACE3 and AmazonFACE4 on subtropical and tropical forests.
The Birmingham Institute of Forest Research (BIFoR) FACE facility is unique in the Northern Hemisphere, and aligns with EucFACE and AmazonFACE to form a global ‘machine’ investigating forest response to elevated CO2. Set in temperate broadleaf


Figure 1. An aerial view of the FACE rings at Mill Haft. Inset: a laser-scan image of the trees for above-ground carbon assesement.

oak-with-hazel woodland (Mill Haft, Staffordshire, UK5), BIFoR-FACE tests hypotheses derived from lab-based and mesocosm studies of forest carbon cycling in a fully-open and complete real-world ecosystem.
Conventional ecological theory suggests that mature woodlands maintain a balanced cycle of carbon, nitrogen, phosphorus and other nutrients. Analyses suggest that contemporary woodland ecosystems are taking up CO2, hence reducing climate change impacts of fossil-fuel burning. Do mature forests have the capacity to increase carbon uptake under elevated CO2, or do other factors limit carbon sequestration? If the system stores more carbon, where will this be allocated (crown, stem, roots or soil)? How do factors like water use and nutrient availability affect carbon allocation? Will the morphology of the trees change?
The aim of this project is to investigate carbon allocation responses of a mature woodland to elevated CO2, with the goal of linking structural responses to underlying function and ecosystem processes. It will use measurements of structure, physiology and growth, and place these results in a global context.

Objectives:
1) To develop quantitative comparisons of canopy structure between control and treatment plots using in-situ and remote sensing techniques, to determine the fast (i.e. first year) and medium-term changes in stand structure and tree morphology;
2) To identify relationships between carbon allocation responses and water-use and nutrient availability;
3) To assess the generality of results through comparison with prior and ongoing (EucFACE, AmazonFACE) studies.

Methodology:
This PhD is part of a major FACE programme investigating the response of mature forest ecosystems to elevated CO2. The FACE facility comprises 9 woodland patches: 3 receiving ambient air plus 150 ppmv of CO2; 3 receiving ambient air using the same infrastructure as those patches receiving extra CO2; and 3 undisturbed patches. Instruments and sampling regimes are already in place for the measurements below; the student will be able to make rapid progress by immersion in a rapidly expanding research team supported by a team of 4 facility technicians.
Aboveground carbon allocation. Stem dynamics will be monitored by web-enabled dendrometers and laser-scanning of stand structure; shoot growth and leaf morphology will be measured in-situ; leaf, flower, and propagule production will be quantified by direct sampling, by leaf-area index (LAI) and leaf mass per unit area (LMA) measurements, and accessing litter collected in complementary projects. Large woody debris will be quantified using structure-from-motion photogrammetry.
A particular focus will be on differential responses between standard oaks and coppice and sub-dominant hazel, sycamore, hawthorn, and holly.
Baseline samples and data are available from years (2015-2016) prior to CO2 fumigation and will form part of the analysis.Corroborative data on nutrients, trophic interactions, and climatology will be available through the consolidated BIFoR-FACE database.

Funding Notes

In addition to completing an online application form, you will also need to complete and submit the CENTA studentship application form available from www.centa.org.uk.

CENTA studentships are for 3.5 years and are funded by the Natural Environment Research Council (NERC). In addition to the full payment of their tuition fees, successful candidates will receive the following financial support.

Annual stipend, set at £14,296 for 2016/17
Research training support grant (RTSG) of £8,000

CENTA students are required to undertake from 45 days training throughout their PhD including a 10 day placement

References

1) Norby, R. J., et al., Model-data synthesis for the next generation of forest FACE experiments, New Phytologist, 2015, DOI: 10.1111/nph.13593
2) Medlyn B et al., 2015. Nat Clim Change 5, 528
3) http://www.uws.edu.au/hie/facilities/EucFACE
4) Lapola D, Norby R, 2013. AmazonFACE Science Plan & Implementation Strategy
5)http://www.birmingham.ac.uk/research/activity/bifor/newsletters/index.aspx