FACE underground:can trees in mature forests gain greater access to soil nutrients under elevated atmospheric CO2?

Lead Research Organisation: University of Birmingham
Department Name: Sch of Geography, Earth & Env Sciences

Abstract

Land ecosystems including forests capture about 30% of the carbon dioxide (CO2) released by human activities. This uptake is mainly attributed to the beneficial effects of increasing atmospheric CO2 concentrations (eCO2) on rates of photosynthesis (the "CO2 fertilisation effect"). Based on current CO2 uptake rates and the predicted increases in atmospheric CO2 concentrations, an attempt has been made to predict future Carbon (C) uptake by forests using different large-scale models. However, the model estimates are highly uncertain because we lack a clear understanding of how the limited availability of soil nutrients, particularly nitrogen (N) and phosphorus (P), regulate the CO2 fertilisation effect. For example, incorporating nitrogen availability into models reduced predicted uptake rates of CO2 by ~50%, which shows that previous estimates may have been optimistic. Furthermore, previous experiments have focused on young forests and to date there are no large-scale CO2 enrichment experiments in mature temperate forests. This is important because: 1) mature forests in northern temperate regions are currently responsible for almost half (~40%) of the global net C uptake and 2) young forests may be able to increase access to nutrients by increasing root growth under eCO2 to explore more of the soil space, whereas mature forests already have well-developed root systems, so greater carbon allocation to roots and their associated fungal partners (mycorrhizas) may have less potential to increase access to nutrients. Therefore, a realistic assessment of the role of nutrient availability in controlling the responses of mature temperate forests to eCO2 is essential.

Given the global significance of temperate forests, the Birmingham Institute of Forest Research (BIFoR), established a CO2 fertilization experiment (>£15 million investment) in a >160 year old deciduous forest stand in Staffordshire in 2017. This is the first such experiment in a mature temperate forests and thus provides a unique opportunity to test a key question: can mature trees gain greater access to limiting nutrients under eCO2 and, if so, which strategies do they employ to do so? Thus, we aim to test the broad hypothesis that under eCO2 a mature, deciduous temperate forest will transfer additional carbon belowground to increase nitrogen and phosphorus availability and subsequent uptake by trees.

The research will be undertaken in three plots under eCO2 and three control plots. We will measure root and mycorrhizal hyphal production, and the release of substrates (exudates) from roots throughout the year. We will also carry out a series of experiments to determine the relative roles of roots versus mycorrhizal fungi in controlling rates of decomposition and nutrient cycling, and the extent to which these are affected by eCO2. These decomposition experiments will involve root and/or mycorrhizal fungi exclusion, as well as a novel approach for simulating root exudation. The results will enable us to determine whether, and through which mechanisms, trees can stimulate decomposition and nutrient mobilization under eCO2. Finally, we will determine if the types of nitrogen containing compounds that roots take up changes under eCO2 and how this relates to their availability in the soil.

In summary, we will use the first FACE experiment in a mature temperate forest to determine whether mature temperate forest trees will be able to access more soil nutrients under eCO2, and therefore, whether there is likely to be a large and sustained carbon sink in these ecosystems, addressing a major uncertainty in carbon cycle modelling. If our results suggest that the forest uptake will become increasingly nutrient limited in the future then it would have major societal implications as greater cuts in greenhouse gas emissions would be needed to avoid the most dangerous consequences of climate change.

Planned Impact

Our project will generate high-quality research that will improve our comprehension of climate change impacts on mature UK woodlands. It will contribute greatly to internationally competitive Discovery Science in the UK, supporting our reputation as world-leaders in the field of global environmental change. The project is highly relevant to the NERC mission and delivers in relation to its strategic plan within the 'Managing Environmental Change' and 'Benefiting from Natural Resources' themes.

Who might benefit from this research? We have identified 6 key stakeholder groups listed below.
1. Academic community: please refer to the 'Academic Beneficiaries' section.
2. Policy-makers such as the UK's Department for Business, Energy and Industrial Strategy; Department of Environment, Food and Rural Affairs (Defra); Forestry Commission; Natural England.
3. Non-governmental organisations (NGOs), especially those working in forest conservation and management, e.g. Woodland Trust, Trees for Life.
4. Forestry groups, land-owners, and industry, e.g. the National Trust, Confederation of Forest Industries, UK Forest Products Association.
5. The general public, who demonstrate a keen awareness of the importance of UK woodlands for climate change mitigation, forest products and human well-being.
6. Regional to global scale coupled CNP and Earth System Modelling communities.

How might they benefit from this research?
Academic community: please see 'Academic Beneficiaries'
Policy-makers, Modelers and NGOs: Our project generates new mechanistic knowledge that will improve the realism of the global earth system models used by the IPCC to predict C capture by forests under future climates. Therefore, our results will have immediate and direct impact on climate change policy globally. The potential for carbon capture and sequestration in forests is a strong incentive for woodland protection and reforestation projects. The UK government is internationally committed to sustainable forest management and current policies seek to ensure that forests are adaptable to projected climate change. Our dialogue with stakeholders and modelers (S. Sitch, L. Mercardo and E. Rowe) suggests that more information is needed on how different forest types will respond to environmental change and influence the potential of forests to store carbon. Our research addresses this to improve our understanding the role of forests in climate change mitigation and the sequestration of atmospheric carbon dioxide. As such, the project will contribute to improving guidelines for reforestation programs to maximize soil carbon storage.
Forestry groups, land-owners, and industry: Forest creation projects are attractive to businesses seeking to reduce their carbon footprints. The UK government has approved the 'Woodland Carbon Code', which validates investment schemes for carbon sequestration. Our research focuses on interactions between above- and below ground processes in forests that could impact upon soil carbon storage under climate change and alter current estimates of carbon sequestration potential.
General public: Forests are highly valued by people in the UK and approximately 250-300 million day trips to forests and woodlands are made each year. Forests are widely acknowledged for their educational value (e.g. Forest Schools scheme), and high public appreciation is evident in membership of organisations such as the Woodland Trust. The high level of pubic interest in the UK and overseas, and the substantial media coverage on threats to forests create an important means by which we can engage with and inform the public about the multiple values of forests and promote awareness of their role in climate change mitigation.
We will target these beneficiaries with a tailored program, including knowledge exchange workshops, attendance of JULES meetings, outreach activities, and public engagement events, which will be supported by the impact advisory panel.
 
Description In the first year of the project (2020) involving field work, we quantified the impacts of elevated CO2 fumigation of the forest on root exudation rates, which were significantly augmented by CO2 fumigation. This finding though preliminary points to a key expectation that CO2 fertilization of forests will enhance belowground carbon allocation to support microbes for seeking nutrients. Further work including metabolomics of the exudates are underway to explore the full breadth of the changes induced by CO2 fertilization and how such changes might help trees seek nutrients to capitalize on CO2 for enhance photosynthesis.

In the second year of the project (20021) we established the fact that root exudation of C increased by 40% in response to elevated atmospheric CO2 concentration and that roots prefer ammonium for nutrition than nitrate. The metabolomics analysis demonstrated changes in the chemistry of root exudates as a strategy by trees to seek nutrients to benefit from the CO2 fertilization.

Decomposition of roots found to be faster than litter and that key extracellular enzymes did not show any trend in response to elevated CO2; however, gross N mineralization increased overall showing shifts in processes as hypothesized in the project originally.

In the growing season of 2023, we set up an automated root exudation system with artificial exudates introduced to soils. The results show key changes in nutrient cycling in response to exudates, where nitrate and phosphate availability have increased. Further analysis is underway to fully explain the tantalizing trends observed initially. A root uptake preference for different N forms for oak trees were undertaken and the data is currently analyzed.
Exploitation Route There is a significant potential for future research innovation and policy recommendations regarding forests response to climate change.
Sectors Environment

 
Description Getting to the root of the forest response to elevated CO2
Amount £20,000 (GBP)
Funding ID Project 1863294 
Organisation Woodland Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 03/2022 
End 03/2024
 
Title Root boxes with double face windows 
Description We designed a root box for installation in soils for accessing roots from time to time for exudates collection and nutrient update preferences studies. 
Type Of Material Technology assay or reagent 
Year Produced 2020 
Provided To Others? No  
Impact An advanced root box design with two sided Perspex window for direct access to roots from trees test and works fine. A method paper will be published on this. 
 
Title BIFoR FACE environmental monitoring data 
Description  
Type Of Material Database/Collection of data 
Year Produced 2020 
Provided To Others? Yes  
URL http://edata.bham.ac.uk/564/
 
Description Metabolomics analysis at Universitat Jaume I, Spain 
Organisation Jaume I University
Country Spain 
Sector Academic/University 
PI Contribution Prof Victoria Pastor at Universitat Jaume I, is our new collaborator, who is not only assisting in metabolomics analysis but in the interpretation of data as well. The analysis and data interpretation is a substantial contribution to the project.
Collaborator Contribution Support in metabolomics analysis and data interpretation. Will provide training to the PDRA on post in metabolomics data interpretation.
Impact Sample analysis Data interpretation support
Start Year 2020
 
Description Targeted metabolomics at Arnold Arboretum and Harvard Forest, Harvard University. 
Organisation Harvard University
Country United States 
Sector Academic/University 
PI Contribution The research group of Dr Ben Taylor, Faculty Fellow at Arnold Arboretum, Harvard University, USA contacted FACE Underground for collaboration on root exudates metabolomics. As a result we are now sending archived samples to Harvard for analysis to be part of a global study on root exudation in response to elevated atmospheric CO2 fumigation.
Collaborator Contribution Ben Taylor group will use our samples and analyse it for 29 target compounds to be part of a global study led by Harvard University. In return, they also plan to undertake further analysis for tracking seasonal changes in exudation via oak tree roots at BIFoR-FACE.
Impact There will be joint publications and sharing of data in the near future. This is a multidisciplinary collaboration.
Start Year 2021
 
Description Demonstration of research activity at BIFoR-FACE to the DEFRA Woodland and Tree Team 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Policymakers/politicians
Results and Impact The DEFRA's Tree and Woodlands Group visited BIFoR-FACE where our project gave a tour of the on-going research under three UKRI-NERC funded projects. Impacts of climate change on forest ecology and restoration of mixed woodlands were the focus of the tour. The key take home was that mixed woodlands are more effective in capturing carbon than mono-cuture-an aspect of your work directly relevant to the DEFRA policy team.
Year(s) Of Engagement Activity 2021
 
Description Showcase of results to UKRI Infrastructure Team at BIFoR-FACE site in May 2022 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Third sector organisations
Results and Impact Showcase of research outcomes at BIFoR-FACE to the UKRI Infrastructure team together with a visit of the FACE facility. The afternoon of the day, also included ECR participation in the UKRI-Infrastructure team for feedback about infrastructure of the future and its impact on science and career development of ECR.
Year(s) Of Engagement Activity 2022