World Soil Day Dec 5: A barren medium or wriggling with life?

Posted 4 December 2014

To mark World Soil Day on Friday December 5, Harper Adams University postgraduate researcher Alexander McCormack explains why soils are important and in particular, the organisms that live within it.

“Soil is often viewed by many as a ‘lifeless’ substance, regarded as merely a matrix in which plants are grown. However, in reality, it is a diverse and complex habitat, containing organisms from all the kingdoms of life; ranging from simple single-celled bacteria to multi-cellular plants, fungi and other organisms.

In one gram of soil, as many as 10 to 100 million bacteria and fungi may be found, along with 10 thousand to one million protozoa (simple animals), and many thousands of nematode worm species.

These organisms all occur together making the soil a similarly rich habitat to that of a tropical rainforest. Similarly, there are also different trophic levels, often beginning with plants and algae which harvest energy from the sun. From this point the food webs expand, including a number of diverse groups of organisms, with many of these being both prey and predator to each other.

One such group, is the phylum Nematoda to which nematode worms belong. Within this group we find a whole food web in itself, from bacterial and fungal eating Rhabditida and plant parasitic Tylenchida, to the exclusively predatory Mononchida. This situation is similar to the rainforest where we might have small plant eating mammals, being predated by large predators such as a Jaguar, so too do large predatory nematodes prey on smaller ones.

The comparison doesn’t just stop there. Although nematodes are often viewed as being all the same, they are hugely variable in both their nature and their appearance.

Nematode mouth parts and their shape are often used as a means of identifying different species, and often offer clues to their role within an eco-system. Those which eat fungi, bacteria or other simple celled organisms, often have simple mouth parts consisting of an open hollow mouth with which to suck in bacteria cells or fungal hyphae.

Herbivores however require more complex mouth parts due to the tough nature of plant cells, which possess a thick lignin wall.  Here, the mouth part has become modified to form a stylet, which is shaped like a hollow needle. Using this it is able to puncture plant cells to access the inner contents off which it feeds, or alternatively move deeper into the plant tissue where it lives as a parasite.

However, one of the more interesting and frightening mouth parts is possessed by the predatory species of nematodes. Here, similar to large predatory mammals such as big cats, these nematode possess an array of large teeth within their mouth parts with which they are able to slice open smaller nematode species in order to devour their inner contents. In fact, many of these toothier nematode resemble the character from Ridley Scott’s Alien, than simple worms with teeth.

Nematodes are just one example to illustrate that soil is not a ‘lifeless’ matrix of ground up rock, but a thriving and living ecosystem comprised of an array of other micro and macro flora and fauna. To this end, it is important that we continue to explore the role of soil and it inhabitants; and more crucially, preserve it for future generations by preventing its degradation."