Mapping world’s soil worms

Multitudes:There are about 57 billion nematodes for every human being on Earth.A. MuralitharanA_MURALITHARAN  

Grab a pinch of soil and you can find over a hundred soil worms or nematodes, says the first global analysis of nematodes. Nematodes are roundworms and their size can vary from a tiny 0.2 millimetre to a few metres.

A team of over 50 researchers collected over 6,500 soil samples from all seven continents of the world and found that there are about 57 billion nematodes for every human being on Earth.

The study was done only on the top 15 cm of soil. Their total biomass comes to around 300 million tonnes which is about 80% of the combined weight of Earth’s humans.

The paper published in Nature adds that these nematodes are responsible for “around 2.2% of the total carbon emission from soils”. Thomas Ward Crowther, one of the corresponding authors of the study from ETH (Swiss Federal Institute of Technology), Zurich adds in a release: “Predicting climate change requires that we understand global carbon and nutrient cycles. We currently have a great understanding of the physics and chemistry of our planet, but we know far less about the biological organisms that drive these cycles. Improving our understanding of these organisms at a global level is critical if we are going to understand and address climate change.”

The most interesting finding of the study is this — at 38% of the total, sub-Arctic regions have the highest abundance of nematodes. The temperate region has the next highest abundance followed by the tropical regions. When asked why the worms preferred the cold regions, Johan van den Hoogen, the first author of the study explained in an email to The Hindu that soil organic matter content was the key driver for nematode abundance. The low temperature and high moisture in the sub-Arctic regions reduce the decomposition rate of organic matter. This leads to accumulation of organic matter and the nematodes happily thrive on them. He is a senior scientist at ETH Zürich, Switzerland

Indian soils

Soils from Western and Eastern Ghats of India and the Himalayas were used for the study. Wasim Ahmad from the Department of Zoology at Aligarh Muslim University was one of the authors of the study and his lab is home to soil samples which have been collected from all parts of India in the past 50 years.

“In India, ever since the 1992 Earth summit, we have started to talk about biodiversity. But the environment ministry has given more emphasis to the ‘above ground biodiversity’, than the ‘below ground biodiversity’. These nematodes play a crucial role in the environment as they are responsible for production of about 19% of ammonia of the soil. They are also important bioindicators of soil ecosystem health,” says Prof. Ahmad.

“Various kinds of bacteria, fungi, arthropods and a wide variety of nematodes inhabit the soil. We can study the environmental changes by looking at a small amount of soil as they can represent the entire food web.” he adds.

Prof. Ahmad is also worried that many nematicides have been indiscriminately used in our agricultural fields, posing a major threat to their survival. He urges the use of biological control methods to save these important organisms.