Peatmoss and Cyanobacteria: Partnering in Carbon Cycling

The Science 

Cyanobacteria such as Nostoc that are living in Sphagnum (peatmoss) resemble plants more than microbes. Like plants, they get their energy from sunlight. Yet they also rely on peatmoss to survive, and peatmoss in turn relies on them. This interaction plays an important role in keeping peatland ecosystems healthy, yet scientists weren’t sure why or how. Now, a multi-institutional study has peered down to the molecular level of these two ecosystem buddies and discovered that low pH enables the formation of the Sphagnum-Nostoc symbiosis, and that Sphagnum produces trehalose sugar for Nostoc and Nostoc provides nitrogen-rich nucleosides and amino acids for Sphagnum. 

The Impact 

Peatlands provide a dramatic example of how changes in the way species interact can cascade through an ecosystem. While peatlands occupy just 3% of the Earth’s land surface, they store ~25% to 30% of the planet’s soil carbon as dead peat. When peatmoss partners with cyanobacteria in a symbiotic relationship, they also provide a critical nutrient, nitrogen, to the environment. By studying interactions between these partners more closely, scientists can tease out what makes them so compatible and how that relationship can be used to predict the way carbon will move through an ecosystem and influence climate processes. 

Summary 

While peatlands occupy only 3% of the Earth’s land surface, they store nearly a third of the planet’s soil carbon, and it is well known that the relationship between peatmoss and its partner cyanobacteria influences carbon storage. Recently, a multi-institutional team of scientists suspected that pH might play a role in establishing the relationship between peatmoss and cyanobacteria. Working under the Facilities Integrating Collaborations for User Science (FICUS) program, the team grew peatmoss and its partner bacteria together at EMSL, the Environmental Molecular Sciences Laboratory, a Department of Energy (DOE) Office of Science User Facility. They then studied the partners using an advanced imaging technique called matrix-assisted laser desorption/ionization mass spectrometry. This specialized imaging allowed them to look at which chemicals were being passed between the two species and under what environmental conditions. They discovered that only when the pH was acidic did the peatmoss release a carbohydrate called trehalose, which the cyanobacteria gobbled up. In turn, the cyanobacteria produced other chemicals, including amino acids and nitrogen-rich nucleosides, that enriched the peatmoss. The team also discovered something they hadn’t expected: cyanobacteria offer sulfur-rich molecules to the peatmoss as well. All told, insights from this study will help scientists predict the movement of carbon and nitrogen in peatland ecosystems. 

Contacts

• David Weston, Oak Ridge National Laboratory, westondj@ornl.gov  
• Dušan Veličković, Environmental Molecular Sciences Laboratory, dusan.velickovic@pnnl.gov 

Funding 

Experimentation and analyses were supported by the DOE Biological and Environmental Research (BER) Early Career Research Program. Samples were collected at the SPRUCE project through DOE BER. A portion of this research was performed under the Facilities Integrating Collaborations for User Science (FICUS) program and used resources at the DOE Joint Genome Institute (JGI) and EMSL, the Environmental Molecular Sciences Laboratory. EMSL and JGI are both DOE Office of Science User Facilities. Additional funding was provided by the National Science Foundation. 

Publication

A.A. Carrell, et al., “Novel metabolic interactions and environmental conditions mediate the boreal peatmoss-cyanobacteria mutualism.” ISME Journal 16, 1074 (2022). [DOI: 10.1038/s41396-021-01136-0]