How do Plants, Fungi and Bacteria compare to each other?
What role do they play in the soil ecosystem?
Bacteria
In 1 gram of soil there are as many as 100,000,000,000 bacteria, roughly 6000 different species [30]. This is the equivalent of all the stars in the Milky Way galaxy [31]!
Bacterial morphology: rods (bacilli), spherical (cocci), comma (vibros), spiral (spirilla) and corkscrew (spirochaetes) [33]. Some have pili and/or flagella. Pili help the bacteria adhere to surfaces like host cells. Flagella are used for locomotion [33].
Bacteria in Soil
Bacteria respond to plant signalling compounds in the soil and form a symbiotic partnership with the plant. If the plant is compatible, cortical cell division is initiated and a nodule is produced on the root hair cell of the plant [32]. This induces bacterial infection in to the nodule site and nutrient exchange can be initiated [32]. These sites for bacterial infection are specialised to ensure only beneficial bacteria infect the root of the plant [44].
One major roles played by soil bacteria is nitrogen fixation. Specialist bacteria produce an enzyme called nitrogenase, this is the only enzyme capable of taking atmospheric nitrogen and converting it to ammonia that can be used by the plant [44]. The plant produced low oxygen concentration nodule, as oxygen can interfere with nitrogen fixation [44].
Image Credit: Fungal Friends
Reproduction
Bacteria have a plasmid which contains genetic information. With the use of a pilus, one bacteria will donate the information in the plasmid. This is how antibiotic information is transmitted between bacteria.
Reproduction is through binary fusion. The bacterial nucleoid containing its DNA divides, the bacterial cell elongates and the genetic information will sit at either end of the elongated bacterial cell. This cell will then cleavage and bud off, forming two genetically identical sister cells [33]. Some bacteria can divide like this every 20 minutes. Therefore; after one hour the bacteria will have grown from one cell to a massive 16,777,216 cell colony [33]!
Number of Species
+30,000
Average Size
2 micron
Image Credit: University of Derby
Fungi
There are over 16,000 species of fungi in the UK alone. Many species do not produce mushrooms, the visible fruiting body. Therefore identification can be a challenge. Genetic techniques are now being used to identify fungal species.
Fungi in Soil
Fungi is made up of fungal cells. Long filamentous cells that release enzymes in to the soil to absorb nutrients [8]. These cells are called hyphae. Hyphae combine to form mycelium. When the fungi needs to release spores, many fungi flush the hyphae with water to make them swell. Hyphae form a fruiting body, the shape determined by the species and this erupts from the soil or wood and matures in to a full mushroom. Then releasing spores [34].
Spores can be projected in explosive packets, released in to the wind to be carried or released in to water.
Image Credit: Fungal Friends
Reproduction
Fungi have a number of reproductive strategies, from asexual to 26 different genders. Fungi of the same species will combine when the hyphal tips recognise each other. Yeast bud off a new yeast cell, which is very different from other fungi [34].
Fungal cells have different sexes or mating types. When the fungi is ready to produce spores, the dikaryons (cells with more than one nucleus, unique to fungi) fuse together and form a gamete. These gametes will have different sexes and will not combine with gametes of the same mating type. They continue their usual fungal life cycle until they meet a gamete of the opposite mating type. They do not necessarily produce spores immediately, the trigger for spore production is poor conditions [34].
When this happens hyphae are flushed with water, a mushroom produced and the spores released. In arbuscular mycorrhiza that do not produce mushrooms, how do they do it? They use vectors. Hyphae are eaten in the soil. Then animals and birds eat those insects. The spores stay alive in the guts of the animal for months, and are deposited. Some will also release spores in to the wind, but this is less common [42].
Image Credit: University of Derby
Number of Species
3 Million
Average cell size
5 microns
Plants
There are almost 40,000 species of plant globally. This figure excludes alga, and moss species. The complex and beautiful structures of the above ground plant are what we think of when we think of plants. However, plants have a dense root structure under ground that is essential for their survival.
Plants in Soil
The rhizosphere refers to the interactions between plant root systems and the nutrient rich soil ecosystem. Plant roots release metabolite compounds (organic acids, amino acids, phenols, and alkaloids) in to the soil that shape the soil structure, microorganisms around the roots and plant biodiversity [41].
Roots work symbiotically with both fungi and bacteria in the rhizosphere to gain the nutrients they cannot gain as effectively alone [24].
Image Credit: Fungal Friends
Reproduction
Looking specifically at angiosperms (flowering plants), their reproduction is complex. Plants produce flowers to attract pollinators. The flower has both male and female parts but mechanisms are in place to ensure plants do no pollinate themselves.
The female part is made up of an ovule, ovary, style and stigma.
The male part is made up of filament, anther and microsporangia (stamen).
Angiosperms will either be thrum (longer stamen and a shorter stigma) or pin (longer stigma than stamen). Flowers have many morphological adaptations to ensure they are pollinated and can therefore produce seed.
Seeds are valuable, but also nutrient intensive. Plants will try to ensure their seeds survive by protecting them in ‘fruit’. This fruit provide nutrients for the seed, or the animals who consumes it. The seeds are then moved away from the origin site by the animal, and ‘planted’ in animals manure. Providing the seed a nutrient rich start.
Image Credit: University of Derby
Number of Species
40,000
Average Cell Size
10 microns
Putting it all together
When plants, fungi and bacteria work together, this enables the plant to adapt to environmental changes, gain natural pest resistance and increase plant nutrients [41].
Individually these small cells seem insignificant, but together they are mighty. Having the power to shape ecosystems, the atmosphere and our behaviour.
Image Credit: Kristina Paukshtite