Soil, not a dirty word, but very, very strange.

It must be a week for soil.

Clown Fish
Scott asked Jill if she was going to decompose the rest of her dinner.

Image: Mike McRae

First I saw this science by email report.

The world under your feet contains a thriving microscopic safari which we know very little about. Scientists only know a fraction of the species of fungi and bacteria that live in soil, and understand even less about what they do. However one thing is certain – they play a key role in how huge quantities of carbon are locked away from the atmosphere and buried.

In considering how carbon is captured and stored by the community of dirty microbes, US researchers have learned we should instead be investigating the role of another common element, nitrogen.

Our atmosphere is made up mostly of nitrogen (N2) gas. Living things need this nitrogen to build proteins and nucleic acids, but it needs to be in a more reactive form than the gas. Bacteria in the soil and the roots of some plants can ‘fix’ N2 and turn it into NH3, or ammonia, which is much easier for the plants to use. Farmers often add extra ammonia as a fertiliser to help their crops grow.

Unfortunately, it hasn’t been clear how adding large amounts of ammonia to the soil affects its diverse range of microorganisms. The researchers analysed soil samples containing different concentrations of reactive nitrogen and measured the numbers of ‘actinobacteria’, a group of bacteria that breaks down plant matter. There appeared to be no difference between their numbers in the experimental and control samples, indicating the nitrogen in fertilisers probably had little impact on the bacteria in the soil.

However when the researchers examined the total variety of DNA sequences in different conditions, they found less in the samples high in reactive nitrogen. Since the scientists don’t know precisely what (or even how many) species of microorganisms are living in the soil, measuring the variety of genes helps them estimate the biodiversity for comparison between the samples. In this case, certain unknown species of microbes may have been unable to tolerate increased amounts of nitrogen being added to their environment.

Given that there was also found to be a difference in the amount of decomposed plant matter between the samples, groups of microbes other than actinobacteria also seemed to be involved in breaking down organic material, impacting on the soil’s carbon cycle.

Understanding how something as tiny as bacteria can impact on something as massive as the world’s climate is crucial in helping scientists predict how our behaviour might impact on the health of our world’s ecosystems.

And then an invite to watch the documentary, “DIRT”.


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