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
Soil

Conserving Soil Biodiversity

Black, fluffy soil with dead plant roots

Like aquatic and terrestrial organisms, soil organisms are threatened by a series of environmental issues. The major threat that they face is habitat loss, which results from land conversion, pollution, climate change and invasive species. Agricultural activities such as “tillage” alter composition of bacterial communities and reduce diversity of soil fungi and larger animals. Construction of roads, buildings and street pavement damage the soil structure and destroy  soil organism’s habitat.

Habitat degradation occurs when the soil is polluted. Pollutants such as heavy metal and excess nutrients change the soil environment chemically, usually in an abrupt and profuse manner. This makes the soil condition unfavourable for many existing soil microorganisms. As a result, only a few pollution-tolerant species survive and dominate the community. The overall microbial diversity and activity decrease. 

The alteration of environmental parameters as a result of climate change also affects soil organisms. Increased concentration of atmospheric CO2 triggers responses of soil fungal communities. Such responses are reflected in the amount of living plants in the area. Quantity and frequency of rainfall and changes of temperature also impact underground animals such as insects. However, the impacts vary by taxon (unit used by scientists to classify organisms) and ecosystem as some are more resistant to environmental changes while some are more vulnerable.  

The intrusion of invasive species such as exotic plants brings changes to the soil environment as well as underground microbial communities.

Their roots release a new combination of chemicals e.g. sugars and enzymes into the soil. The type and amount of chemicals are different from the ones released by original plant communities. This affects the activity and population size of microbial community at the rhizosphere i.e. portion of soil surrounding roots of living plant as its biological and chemical properties are influenced by the roots. The invasive plants also impact the soil organisms by interfering with nutrient cycling e.g. the legume plants, or changing the amount of litter and root inputs. 

Conservation measures to support soil biodiversity include managing natural areas, restoring degraded ecosystems, adopting sustainable farming practices and adapting urban areas for both nature and people. Identifying undisturbed land and protecting it are important to sustain soil biodiversity as the habitat quality of soil organisms is maintained. Other than that, both artificial and natural revegetation of disturbed land help soil microbes and fauna to re-establish. 

Dry leaves are used for mulching and composting. They help to retain soil moisture, regulate soil temperature and suppress weed growth.

Sustainable farming practices are also important in conserving soil biodiversity. Reduced tillage, crop rotation, planting of cover crop and retention of litter are some useful measures to improve soil quality as well as support soil biodiversity. Allocating spaces for greenery and wildlife in urban planning, establishing green roofs and rain gardens, reduced soil compaction and using mulch as groundcover are some of the ways that encourage soil biodiversity in urban areas.

References: 

Alizabeth M. Bach, K. S. (2020). Soil Biodiversity Integrates Solutions for a Sustainable Future. Sustainability, 2662. 

Nihorimbere, V., Ongena, M., Smargiassi, M., & Thonart, P. (2011). Beneficial Effect of the Rhizosphere Microbial Community for Plant Growth and Health. BASE, 327-337. Retrieved from https://popups.uliege.be/1780-4507/index.php?id=7578