Quantifying and upscaling nitrogen fixation in pristine ecosystems: Uncovering the climatic, ecological, and molecular control mechanisms

Project Information

SYMBIONIX

Grant agreement ID: 947719

DOI

10.3030/947719

Project closed

EC signature date 8 October 2020

Start date 1 February 2021

End date 30 June 2026

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 451 171,00

EU contribution

€ 1 451 171,00

Coordinated by

KOBENHAVNS UNIVERSITET
Denmark

Periodic Reporting for period 3 - SYMBIONIX (Quantifying and upscaling nitrogen fixation in pristine ecosystems: Uncovering the climatic, ecological, and molecular control mechanisms)

Reporting period: 2024-02-01 to 2025-07-31

Summary of the context and overall objectives of the project

Plant productivity in boreal forests and tropical cloud forests is limited by the generally low availability of soil nutrients, primarily nitrogen (N), and these ecosystems are also the most vulnerable systems to climate change. Mosses account for a large fraction of ecosystem productivity in these habitats; and most of them are colonized by N2-fixing cyanobacteria, thereby providing plant-available N to the ecosystem. Despite this key role, critical knowledge gaps exist. For instance, the climatic controls of moss-associated N2 fixation are severely understudied, limiting our capability to predict climate change effects on this fundamental ecosystem function. Further, it is unknown whether mosses and associated N2 fixers share a mutualistic (both partners benefit) or parasitic (one partner benefits at the expense of the other) relationship. Yet, the balance of this association is crucial for maintaining ecosystem productivity. Current ecosystem models do not incorporate moss-associated N2 fixation, and thereby, significantly underestimate ecosystem productivity. In SYMBIONIX, we will combine field, laboratory and modelling approaches to fill these knowledge gaps in four interlinked Research Tracks (RT) by addressing four objectives:

RT1 Climatic Controls: To identify the climatic controls of N2 fixation in mosses from contrasting ecosystems: boreal forests and tropical cloud forests.
RT2 Molecular Controls: To ascertain the molecular traits defining the degree of mutualism or parasitism in moss-cyanobacteria associations using comparative transcriptomics.
RT3 Cellular Controls: To determine the nutrient exchange between moss and cyanobacteria using nanoSIMS (nano scale secondary ion mass spectrometry).
RT4 Synthesis: To model ecosystem N input via N2 fixation in boreal forests and tropical cloud forests.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Since the grant began, my team and I have published 4 papers directly derived from work in SYMBIONIX (including one invitation for a Tansley Insight article in New Phytologist; one based on undergraduate research in my group etc.), and I have supervised and/or am supervising 4 PhD students, 1 postdoc, 3 MSc, 9 BSc students and 3 research project students.

We have performed 3 successful field expeditions – 2 to tropical cloud forests in Costa Rica and 1 to tundra sites in Northern Sweden (August 2021 to Northern Sweden, November 2021 and January 2023 to Costa Rica). We have set up long-term nutrient addition experiments in two forest types in Costa Rica (primary forest and natural regrowth) and have collected samples along steep elevation gradients along the highest mountain in Costa Rica, Chirripo, 3800m. At the arctic sites, we have collected samples from long-term nutrient addition experiments as well as from warming experiments.

Key papers for RT 1 have been published (in Plants, Acta Oecologia, New Phytologist, including press release) highlighting the importance of micronutrients for moss-associated nitrogen fixation in tropical forests, while temperatures are key for nitrogen fixation in arctic settings assessed in large scale field and laboratory settings.

We have optimized protocols to be able to grow moss and cyanobacteria independent of each other, which is a pre-requisite for the transcriptomic work (research track 2). We have completed the first transcriptomic experiment which is currently under review for publication in a scientific journal, and we completed a more expansive experiment (data being currently analysed) which will be key to fulfil objectives for RT2.

The team has participated in different international conferences including as keynotes at e.g. the Congress of the European Society for Evolutionary Biology, Prague, 2022; and has disseminated results with e.g. a popular talk for the Botanical Society in Lund, Sweden, 2022, and we featured in Trends in Microbiology’s initiative to highlight voices of early career researchers (“ECR in Focus”), 2022.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Boreal as well as tropical ecosystems are amongst the most vulnerable systems to climate change, which threatens a wide range of critical ecosystem services provided by these ecosystems as repositories of carbon and endangered species. This renders immediate assessments of climate change effects on these systems necessary and urgent. The results of SYMBIONIX will enable us to define the role of moss-cyanobacteria associations for the N cycle in a future climate, with fundamental implications for ecosystem productivity.
Progress in ecosystem research is often hampered by our lack of understanding of how limiting factors vary markedly across scales. SYMBIONIX offers the novel opportunity to combine biogeochemistry with ecology across scales, providing a break-through in ecosystem research. Here, I will uniquely interlink a key ecosystem function (RT1) to its molecular (RT2) and ecological underpinnings (RT3). A synthesis of these RT’s will be accomplished via the parameterization and validation of current global circulation models (RT4). By assessing the molecular traits of moss-cyanobacteria associations, and functionally verifying these molecular mechanisms with the nutrient transfer between moss and colonizing cyanobacteria, my research group will undertake the first comprehensive attempt to place them along the mutualism-parasitism continuum. Further, by assessing the effects of abiotic factors (N availability) on the nutrient trade between moss and cyanobacteria, I can reveal how the balance between the partners is affected by N availability. This will also enable us to predict how the degree of mutualism or parasitism between moss and cyanobacteria will be affected by increased N input to pristine ecosystems. A decoupling of nutrient exchange mutualisms via increased N input may affect the entire ecosystem N budget and consequently, ecosystem productivity.
Current ecosystem circulation models do not incorporate moss-associated N2 fixation, thereby misrepresenting ecosystem N inputs. Consequently, my group will offer a significant revision of major global circulation models. By being incorporated into an Earth system model that will participate in the international endeavour to inform the next IPCC Assessment, the fundamental science insights generated from this project will have a direct pathway of impact. Thus, the results of this project will have relevance for international policy advice on climate change. Furthermore, by modelling the resource optimization of moss-associated N2 fixation, my research team can estimate where and under which conditions N2 fixation in mosses occurs. This will facilitate focussed search in unexplored systems, which could lead to the discovery of N2 fixation in ecosystem types and areas that have been thought to lack any N2 fixation capabilities to date.
Our research is one of the first identifying the controls of moss-associated nitrogen fixation in tropical cloud forests. These forests are sensitive to climate change and our results will help estimate changes to nutrient cycling in a future climate. We will further identify the bacterial communities on the moss and compare those to the ones found in arctic and boreal mosses. This will shed light on habitat specific adaptations and associations. Further, we will be able to show how sensitive different moss-cyanobacteria associations are towards climate change.

Example of a field plot covered with mosses in a tropical cloud forest in Costa Rica

Mosses in a tropical cloud forest in Costa Rica