Most soil is made up of bacteria, viruses and fungi. The finding will have an impact on carbon disposal and climate change, according to a DCU research team, writes Aine Bird
SOIL MAY NOT be something you think about often, after all it's just dirt, isn't it? If you believed that, the recent discovery by researchers in Dublin City University that up to 60 per cent of soil consists of living or once-living micro-organisms will come as a surprise.
"Traditionally, it was thought that soil was made up of a mysterious material called humic substances, but we've shown it's mostly made up of microbes," says Dr Brian Kelleher, from the school of chemical sciences in DCU.
It was originally believed that the amount of carbon in soil derived from micro-organisms was between 1 per cent and 5 per cent, but in reality it accounts for at least 50 to 60 per cent, according to a recent research paper published by Kelleher and his collaborators. Micro-organisms in the soil include bacteria, fungi and viruses.
"This means that it changes everything around. If most of the carbon is derived from micro-organisms, we have to look at and study the carbon in soil in a very different way. Previously we were getting lead down other paths where we're less likely to understand the form the carbon is in."
Soil is one of the environment's main carbon stores, holding more carbon than the atmosphere. So what effect could climate change have on all this stored carbon? The work currently being undertaken by Kelleher and his team may go some way to answering this question.
"We're working on natural organic matter including carbon in the soil. There are huge amounts of carbon stored in ocean sediments and soil, the problem is we don't know the chemical characteristics of this carbon," explains Kelleher.
"If in the future there is a one or two degree temperature change, what will happen? There is a possibility that the carbon will be released into the atmosphere. There is also the carbon that is being added through agriculture with fertilisers. It's a mystery how the soil carbon reacts with temperature change and fertilisers," he suggests.
As well as helping predict what effect climate changes could have on carbon in the soil, this research could also benefit agriculture. "People apply fertiliser and hope for the best. Some sticks but a lot can end up in water. We don't know the chemical composition of the carbon in the soil at the moment so we can't formulate fertilisers to stick to them," Dr Kelleher says.
The work is in collaboration with researchers at the University of Toronto, where they are using a technique similar to the medical MRI, called Nuclear Magnetic Resonance (NMR). "NMR allows us to look at the soil organic material at a molecular level and see all the organic matter. We can't say exactly what they are but it gives us something like a fingerprint. This is a relatively new technology in environmental chemistry," Kelleher says.
"If we're underestimating the microbial content in soil, are we also underestimating the microbial carbon sequestering in soil? Traditionally it was thought that carbon sequestering was mainly through photosynthesis in plants," says Kelleher.
Queen's University Belfast will join DCU and Toronto to work on the next phase of the project which will investigate this question. "We will be trying to find out if and what species are taking up CO2 and look at their characteristics. If we can identify the species, maybe agricultural practices which enhance their growth could be used. This could increase CO2 uptake and soil organic carbon which is win-win."
The research paper Microbially Derived Inputs to Soil Organic Matter: Are Current Estimates Too Low? was published in Environmental Science and Technology. Research was funded by Science Foundation Ireland and the Environmental Protection Agency