Categories
Soil

Soil Biodiversity

Bacteria, insects and earthworms break down organic materials e.g. fruit peels and dry leaves in the composting bin. Same goes to the real soil
Bacteria, insects and earthworms break down organic materials e.g. fruit peels and dry leaves in the composting bin. Same goes to the real soil

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. 

A pleasing fungus beetle feeds on fungus and decomposing matter.

Cave cricket lives in leaf litter.

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/

Categories
ecosystem

Saving the Underground Farmers: Soil Ecosystems

Have you ever noticed the earth that you step on?

It is where we get materials essential to our survival. It is soil that supports the growth of plants, the producers of the food chain and the sources of fibre, fodder, and fuel.

At first look, it seems static and lifeless. In fact, soil hosts millions of life forms including bacteria, fungi, insects and other invertebrates, that all interact and perform complex activities. Some of these consume other life forms, others compete for space and resources, and certain organisms form collaborative relationships to access resources.

image of earthworm and soil
Earthworms are important members of the underground soil community affecting physical structure of soil

Underground life forms collectively form the soil biota and continuously re-construct the soil environment. These underground farmers are important to ensure healthy development of a plant, as the roots of the plant are a part of the soil ecosystem.  

The Mutualistic Relationships between Plants, Soil Microbes and Fungi

The underground parts of plants carry out nutrient and water uptake from the soil. The root system of a plant is involved in plant-microbe interaction whereby the plant provides carbons and shelter to the microscopic soil organisms (microbes). The microbes in turn supply minerals and trace elements in a modified form that can be used by the plant.

An example of such interaction is that of legume plants (peas, beans) and nitrogen-fixing bacteria. The bacteria in the soil convert nitrogen from the air into a form that legume roots can absorb from the soil.

Plants also develop symbiotic associations with soil fungi, that is, the relationship benefits both the plants and the fungi. These fungi reside near to or within the root cells of the plants.

Soil fungi use the organic nutrients and sugars that are produced by the plants. In return, they benefit plants by improving the plants’ ability to absorb nutrients and water, and their resistance to unfavourable conditions like pollution and diseases.  

The Alteration of Soil Structure and Composition

Over recent decades, large-scale industrial farming and land conversion have resulted in great change of soil structure and composition. The clearing of trees, shrubs and grasses, the digging and overturning of topsoil using machinery, as well as application of chemical insecticides, herbicides and fertilisers have had disastrous impacts on the underground food web.

The soil environment has become less conducive for the organisms to survive. The soil microbial communities lose connection with plant roots that provide carbons and shelter, and in turn the plants’ capacity for taking up water and nutrients declines. The soil ecosystem is losing its viability and robustness. 

Promoting healthy soil ecosystems

In order to revive the fertility of soil, we need to bring back the carbon to the soil. This is important for ensuring food security and sustainability of agricultural activities.  Here are two ways we can do this:

  • Plant different varieties of plants–each plant variety releases a unique set of biological compounds to the surrounding of its root system, and signals different underground microbe community and fungi. The greater the plant variety, the greater the variety in soil microorganisms which improves soil water-retention capacity and nutrient availability.
    Besides soil improvement, more plant varieties result in a greater variety of insects, including predatory insects that feed on pests. The predators help control pest numbers and thus reduce physical damage to the crop plants. 
Soil ecosystem consists of life forms that live within the soil but it also provides food to above-ground organisms
Image credit: USDA (CC-0)
  • Limit the use of chemical fertilizers—The application of NPK fertiliser has to be reduced, so that soil microbial communities have the chance to thrive and re-connect with the plant roots. Instead of relying on chemical input, plants have to derive these essential elements from the underground microbial communities and in return, channel their carbons to the soil. The increase of soil carbon would boost the soil communities, improve nitrogen uptake and also help maintain the structure of soil.  The removal of excess fertiliser reduces the formation of nitrous oxide (a greenhouse gas) in waterlogged or compacted soil.

Summary

If we understand soil and the life it teems with, we can grow healthier plants and do so in a sustainable manner. We can avoid the excessive chemical and water use that is a growing concern.

Plant growth is influenced by the health of the soil and it also influences life around it and beneath it. Having more plants of different varieties helps conserve underground ecosystems. As the soil carbon (provided by plants) increases, the soil microbial community is revived, and the underground farmers can improve the structure and composition of the soil to support more plants.

Reference:

Jones, C. (2018). Light Farming: Restoring carbon, organic nitrogen and biodiversity to agricultural soils . Retrieved from Amazing Carbon Web site: http://amazingcarbon.com/JONES-LightFarmingFINAL(2018).pdf