Soil Biodiversity

Soil organisms constitute more than 25% of discovered biodiversity on earth. However, much of them remain unexplored and receive little attention compared to aboveground organisms.

Though less visible, these organisms are responsible for various ecosystem functions such as:

• nutrient cycling
• pollution remediation
• disease control
• water infiltration
• supporting agro-ecosystems etc. 

The ecological processes in soil are mainly driven by interactions between soil microorganisms and plants, especially their underground roots. The soil microbes (microscopic organism), mainly bacteria and fungi, break down dead organic matter e.g. fallen leaves and release minerals and carbon compounds into the soil. These nutrients will be reused by plants for development. Some microbes establish mutualistic relationships with plants. For example, the mycorrhizal fungi transport water and minerals to the plant, while they receive carbon in return. 

The soil microbes also suppress plant diseases by competing with disease-causing organisms, colonising or consuming them.

Soil microorganisms are important in maintaining soil structure and retaining water.

The sugar-rich secretion of bacteria or threadlike filaments of fungi bind soil particles into small aggregates which are physically and chemically stable.

The microbes are eaten by larger soil organisms i.e. the protozoa and nematodes. These small animals are then eaten by their predators such as insects, centipedes, spiders and scorpions. This underground food web is connected to aboveground food web as soil-dwelling animals become the food source of animals that live on the ground such as birds, snakes and frogs. 

Aside from organisms in the grazing food chain, there are animals that feed on dead plant materials. Unlike decomposer, these animals need to orally ingest the organic matter and digest it inside their bodies. Some examples of these detritus-feeders are woodlices, beetles and termites. 

Apart from that, the earthworms which feed on leaf litter and soil are known as ecosystem engineers as they produce nutrient-rich castings and create pores in soil. The castings are important for soil aggregate formation and plant growth, while the pores in soil facilitate water movement, increase water infiltration and alleviate flooding.  

Reference:

1. Ingham, E. R. (n.d.). Soil Bacteria. Retrieved from USDA Natural Resources Conservation Service Web site: https://www.nrcs.usda.gov/wps/portal/nrcs/detailfull/soils/health/biology/?cid=nrcs142p2_053862 
2. Biologydictionary.net Editors. (2017, November 05). Difference between Detritivores and Decomposers. Retrieved from https://biologydictionary.net/difference-detritivores-decomposers/