Mucus ‘glue’ helps soil store carbon, research finds

Sticky substances released by living microbes can make an important contribution to carbon storage on soil minerals, according to new research.

Microbes are known to build up carbon storage in soil – helping regulate the global carbon cycle and climate – though previous studies have mainly focused on the remains of dead microbial cells in this process.

However, new research led by the Huazhong Agricultural University in collaboration with the University of Leeds – with the Royal Horticultural Society as a research partner – indicates that living microbes also make a major contribution by releasing sticky, mucus-like substances made of sugars, proteins and other compounds.

Researchers used an isotope tracing method to quantify the production of extracellular polymeric substances, mucus-like mixtures of sugars, proteins, and other biopolymers released by microbes, which was applied across cropland soils in China. They found that microbes produced these substances at rates comparable to the production of cellular material.

Further isotope labelling experiments showed that carbon from these substances could become attached to soil minerals, at levels comparable to, and in some soils greater than, carbon from microbial cells. These results suggest that this previously overlooked “microbial glue” pathway could be an important part of how carbon becomes stored in soils and therefore influence our understanding of the global carbon cycle.

Building a picture of how healthy soils function

Professor Caroline Peacock, from the School of Earth, Environment and Sustainability, said: "We tend to think of microbes contributing to soil carbon after they die, but this work shows that they can also help build soil carbon while they are alive.

“The sticky, mucus-like substances they release can become incorporated into mineral-associated carbon just as much as, and in some soils more than, material from microbial cells. This reveals a previously overlooked route by which microbes can help lock carbon into soils.”

The findings are also significant for those working on agricultural soils and carbon management, as understanding these processes is essential for predicting how soils will respond to environmental change.

Marc Redmile Gordon, Soil and Climate Change Scientist at the RHS, said: “Microbes are fundamental to healthy, functioning soils. This research provides new evidence that the ‘microbial glues’ produced by living microorganisms can contribute substantially to the formation of carbon associated with soil minerals.

Understanding these processes helps us build a much clearer picture of how healthy soils function and how carbon moves through and is retained in soils and ultimately helps the RHS research the gardening practices that promote this process.

Dr Peng Cai, Professor of Environmental Soil Science and Biogeochemistry at Huazhong Agricultural University, said: “These results identify the extracellular pathway as an important and previously underappreciated mechanism contributing to the mineral-associated carbon pool and provide mechanistic insights into how microbiomes shape the fate of soil carbon under global change.”

Read the paper in Nature Geoscience here. 

Main image: Rice field in China by Marianne Bos, Unsplash