Where there’s muck, there’s brass | Rothamsted Research
https://www.rothamsted.ac.uk/news/where-there%E2%80%99s-muck-there%E2%80%99s-brass
Soil as an extended composite phenotype of the microbial metagenome
https://www.nature.com/articles/s41598-020-67631-0
“Despite carbon’s critical role, the mechanisms underlying carbon dynamics and the link to soil water were poorly understood,” said Neal. “Society struggles with the concept of what soil is and how it can be managed effectively because it is such a complex combination of biological, chemical and physical processes.
“We took inspiration from a theory proposed by Richard Dawkins in the 1980s that many structures we encounter are in fact products of organisms’ genes – Dawkins used the examples of bird nests and beaver dams. This view helped us understand soil as a product of microbial genes, incorporating organic materials from plants and other inputs to create all-important structure.
“We have shown for the first time a dynamic interaction between soil structure and microbial activity - fuelled by carbon - which regulates water storage and gaseous flow rates in soil with real consequences for how microbes respire.”
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In healthy soils, relatively low nitrogen levels limit microbes’ ability to utilise carbon compounds, so they excrete them as polymers which act as a kind of ‘glue’ - creating a porous, interconnected structure in the soil which allows water, air, and nutrients to circulate.
Writing in the journal Scientific Reports, the researchers reveal that the Victorian-era switch from manure to ammonia and phosphorous based fertilizers has caused microbes to metabolise more carbon, excrete less polymers and fundamentally alter the properties of farmland soils when compared to their original grassland state.
Lead researcher Professor Andrew Neal said: “We noticed that as carbon is lost from soil, the pores within it become smaller and less connected. This results in fundamental changes in the flow of water, nutrients and oxygen through soil and forces several significant changes to microbial behaviour and metabolism. Low carbon, poorly connected soils are much less efficient at supporting growth and recycling nutrients.”
A lack of oxygen in soil results in microbes having to turn to nitrogen and sulphur compounds for their energy – inefficient processes, he says, which result in increased emissions of the greenhouse gas nitrous oxide among other issues.
The closed soil structure also means microbes need to expend more energy on activities such as searching out and degrading less easily accessible organic matter for nutrients.
Conversely, in carbon-rich soil there is an extensive network of pores which allow for greater circulation of air, nutrients and retention of water.
“Manure is high in carbon and nitrogen, whereas ammonia-based fertilisers are devoid of carbon. Decades of such inputs - and soil processes typically act over decades - have changed the way soil microbes get their energy and nutrients, and how they respire.”
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long term addition of nitrogen and phosphorous fertilizers has caused microbes to burn more of these carbon compounds for energy, an activity that has increased emissions of CO2.
Ploughing has also increased the availability of this soil carbon to microbes, further decreasing its levels in the soil.
As carbon stocks decline, less EPS is produced, and the soil loses the beneficial porous structure