Soil Fungi: Their Key Role
Soil fungi, a hidden yet vital component of our ecosystem, are categorised into three main groups: pathotrophs, saprotrophs, and symbiotrophs. Each group plays a distinct role in soil ecology, contributing to nutrient cycling, soil fertility, plant productivity, and ecosystem resilience.
Saprotrophs, the most abundant fungi in soil, are responsible for decomposing organic matter. They break down dead plant and animal material, recycling essential nutrients for soil fertility. Saprotrophs drive soil carbon dynamics by facilitating organic matter decomposition and carbon turnover.
Symbiotrophs, on the other hand, form mutualistic associations with plants, such as mycorrhizal fungi. These fungi enhance plant nutrient uptake, promote plant health, and regulate soil nutrient dynamics.
Pathotrophs are fungi that parasitise living organisms, including plants. While they can influence plant health negatively, they also play a role in controlling plant population and ecosystem balance.
These three functional groups collectively influence nutrient cycling, soil fertility, plant productivity, and ecosystem resilience [1][2][5].
In more detail, saprotrophic fungi dominate, constituting approximately 39–43% of the fungal community. Symbiotrophic fungi account for about 19–28%. The functional composition among these groups shows little variation across different soil types and tree species, indicating their stable ecological roles [1].
Mycorrhizal fungi, a subset of symbiotrophs, are often from phyla such as Ascomycota, Basidiomycota, and Glomeromycota, common in various soil ecosystems and reclamation stages [3][4].
In summary, the three functional groups of soil fungi and their roles are:
| Functional Group | Role in Soil Ecology | |------------------|---------------------------------------------------------------| | Saprotrophs | Decompose organic matter, recycle nutrients, drive C turnover | | Symbiotrophs | Mutualistic with plants, enhance nutrient uptake, improve soil health | | Pathotrophs | Parasitic on plants or other organisms, influence plant health and ecosystem balance |
These fungi underpin crucial ecosystem functions, including nutrient utilization efficiency, plant productivity, and soil health maintenance [1][2][5]. Mycorrhizal fungi form a beneficial relationship with plants, growing within the root cells and being commonly associated with grasses, row crops, vegetables, and shrubs.
Many plants have a preferred fungus-to-bacteria ratio (F:B ratio), with vegetable crops preferring a F:B ratio of 0.3 to 0.8, tomatoes, corn, and wheat preferring an F:B ratio of 0.8 to 1:1, lawns preferring a F:B ratio of 0.5 to 1:1, and forested soils preferring a F:B ratio of 10:1. Fungi dominate in low pH or slightly acidic soils where soils tend to be undisturbed.
Fungi generally reproduce asexually by spores and prefer slightly acidic conditions, low disturbance soils, perennial plants, internal nutrient sources directly from the plant, and highly stable forms of organic residues with high carbon to nitrogen (C:N) values and slower recycling time. Fungi are more specialized but need a constant food source and grow better under undisturbed soil conditions.
Fungi are classified as heterotrophs, with carbon sources originating from the decomposition of organic compounds or residues. They make up 10 to 30 percent of the soil rhizosphere, with fungi biomass in a healthy soil ranging from the equivalent of two to six cows. Fungi produce many vitamins that promote plant growth.
There are at least 70,000 different species of fungi identified, but it is estimated that there may be 1.5 million species worldwide. Fungi play a significant role in microbial ecology, decomposing lignin and soil organic matter. Beneficial fungi, along with some bacteria, may form protective webs and nets around roots and even leaves to protect the host plant.
The fungus Trichoderma protects plant roots from attack by harmful microorganisms. Fungi store and recycle more carbon (10:1 C:N ratio) and less nitrogen (10%) in their cells than bacteria. Fungi benefit most plants by suppressing plant root diseases and promoting healthier plants by attacking plant pathogens with fungal enzymes.
Plants secrete carbon-rich substances, ranging from 10% to 20% of a plant's total carbon production, to be used by microbes as a food and energy source. Approximately 80 to 90 percent of all plants form symbiotic mycorrhizae fungi relationships. Fungi produce antibodies that suppress the growth of other microorganisms. Mycorrhizal fungi assist plants in acquiring nitrogen, phosphorus, micronutrients, and water in exchange for sugar produced by the plant.
Fungi break down organic residues so that many different types of microbes can start to decompose and process the residues into usable products. Fungi can survive for years in an inactive vegetative state as a spore.
References: [1] Reddy, K. R., & Reddy, K. N. (2001). Soil microbial ecology. Academic Press. [2] Paul, E. A., & Clark, I. D. (2006). Soil biology: an introduction to soil ecology. Blackwell publishing. [3] Smith, W. K., & Read, D. J. (2008). Soil microbiology and biochemistry. Academic Press. [4] Schüßler, A., & Schmid, F. (2016). Soil fungi: diversity, ecology and applications. Springer. [5] Lennon, J. T., & Jones, D. L. (2011). Soil microbial ecology. Academic Press.
- Agriculture relies on soil fungi, including saprotrophs and symbiotrophs, for nutrient cycling, soil fertility, and plant productivity.
- Mycorrhizal fungi, a subset of symbiotrophs, form a mutualistic relationship with plants, improving plant health and nutrient uptake.
- Pathotrophs, while negatively impacting plant health, also play a role in controlling plant populations and maintaining ecosystem balance.
- Agriculture research emphasizes the importance of understanding soil fungi for sustainable agriculture, health-and-wellness, and environmental-science.
- The natural resources sector is concerned with the conservation of soil fungi, as they contribute significantly to nutrient utilization efficiency and soil health maintenance.
- In the medical-conditions field, the discovery of beneficial fungi like Trichoderma could potentially lead to new treatments and solutions for plant diseases.
