Research Highlights

Mapping the world's soil-living worms

doi:10.1038/nindia.2019.101 Published online 5 August 2019

Map of sample locations and abundance data.

© Hoogen, J. et al.

Earth scientists have created global maps of nematodes, a type of microscopic worm that inhabit the top layer of soil from the frigid Arctic and the Arabian Desert to the Himalayas1. They have found that the worm populations are denser in the cold regions than in the deserts.

The total biomass of these worms is actually three times greater than previously estimated and represents more than 80 per cent of the total human biomass on Earth. Such data will be useful for understanding the overwhelming abundance of life in soil and its influence on the global ecosystem.

To shed light on the abundance of these worms, an international research team, including a scientist from the Aligarh Muslim University, India, produced the maps by analysing soil samples from various locations.

The resulting maps show that all the worms have a biomass of 0.3 gigatonnes. Almost 40 per cent of these creatures exist in boreal forests and the tundra, 25 per cent in temperate regions, and the rest in tropical and sub-tropical regions.

The worms’ densities, the researchers say, fluctuate in line with varying concentrations of soil organic carbon (SOC) and other factors such as soil texture, pH levels, temperature and rainfall.

SOC is used as a nutrient by bacteria and fungi, on which the nematodes feed. So, higher SOC helps increase the nematode populations by enhancing the amount of bacteria and fungi.

These worms exhale carbon that is roughly equivalent to 15 per cent of the carbon emissions from fossil fuel use, or around 2.2 per cent of the total carbon emissions from soils. This indicates that the worms play a vital role in global soil carbon cycling, the researchers add.


References

1. Hoogen, J. et al. Soil nematode abundance and functional group composition at a global scale. Nature (2019) doi: 10.1038/s41586-019-1418-6