In this work “The diversity of fungi in potting soil”. The effective microbiological standard method was used to isolate fungi from four different potted soil samples from four different sites in Owerri, Imo State.
An appropriate result was obtained after the inoculation and the incubation in which some fungal growth were observed in macroscopic which are; Aspergillus spp, Geotrichum spp, Penicillium spp., Mucor spp., Trichosporon spp.
In conclusion, some fungi are very harmful i.e. they can cause food spoilage, they can also cause disease to plants, animals and even man.
In recommendation, potting soils are good inhabitation of fungi and also good sites for the isolation of various fungi which are useful for both agricultural and industrial purpose and they also provide mankind with very useful pharmaceutical products like antibiotics.
Soil can be defined as the organic and inorganic materials on the surface of the earth that provide medium for plant growth. Soil develops slowly over time and is composed of many different materials (C.H Robinson, & Beckett, J.; 1997). Inorganic materials, or those materials that are not living which include weathered rocks and minerals. The rocks are broken down into smaller pieces through chemical process known as weathering. As the rocks are broken down, they mix with organic materials, which are those materials that originate from living organisms. (I.A Torsvik et al.,). For example, plants and animals die and decompose, releasing nutrients back into the soil.
1.1.1 TYPES OF SOIL
There are three basic types of soil: sand, silt and clay. But, most soils are composed of a combination of the different types. How they mix will determine the texture of the soil i.e how the soil looks and feels.
Sand is actually particles of weathered rock. Sand is fairly coarse and loose to enable water drain through it easily. While this soil is good for drainage, it is not good to grow plants with because it will neither hold water nor hold nutrients.
Silt is another type of soil that is fine and can hold water better than sand.
Clay is a very fine grained soil. Its parties are even smaller than that of silt, so there is very little space between the fine grains for air or water to circulate. Therefore, clay does not drain well or provide space for plant roots to flourish.
Now, we can consider loamy as the fourth type of soil because it is the combination of sand, silt and clay.
1.1.2 SOIL STRUCTURE AND TEXTURE
The knowledge we acquired in the study of the types of soil told us about the soil texture, which really comes down to the size of the particles and how much of each particles is present.
The soil structure is based on the arrangement of individual particles of sand, silt and clay. When these individual soil particles bound together, they form soil aggregated. (I.A Torsvik et al).
1.2 IMPORTANCE OF SOIL
Soil is very important in the following aspects:
Soil has vital nutrients for plants. As a result, it is used in agriculture to nourish plants. The roots of a plant receive nutrients from the soil to help it grow. (Molin; 1997)
Clay soil can be used in making ceramics, or pottery. When water is added to clay soil, it can be used to create the ceramics. Once formed, allow it to dry and it will retain its shape. Some types of ceramics that can be created with clay soil are vase, cup, bowl etc. (Molin; 1997).
Soil is an important part of the building process. Soil compaction increases the density of the soil, the purpose is to improve the load support. If not done, structural failure can result. Soil can also be used as building materials such as red bricks (Molin; 1997).
1.3 MICROOGANISMS IN SOIL
Soils are the naturally physical covering of the earth’s surfaces and represent the interface of three material states. Solids (geological and dead biological materials), liquids (water), and gases (air in soil pores).(Dighton J., H.E Jones, et al; 1997).
Soil microbes, bacteria, archaea, and fungi play diverse roles in these ecosystem services. The rest metabolic diversity of soil microbes means their activities in the soil and functions of soil ecosystems as well as the ability of soils to provide services to mankind (Wall, A., 1999).
Bacteria and archaea are the smallest independently living. Single-celled organisms on earth. Typical cells range from 0.5 to 1.0um in diameter. Bacteria and archaea may occur as cocci, rods, or spirals. Bacteria are extremely metabolically diverse and can be divided into four groups, based on their source of carbon and their source of energy.
Photoautotrophs: like cyanobacteria photosynthesis, obtaining energy from sunlight and carbon by fixing carbon di oxide.
Photo heterotrophs: they derive energy from photosynthesis if provided with an election donor (hydrogen or an organic compound) for reductive assimilation of carbon dioxide.
Chemoautotrophs: they use reduced inorganic substrates to fix carbon dioxide and as a source of energy.
Chemo heterotrophs: they require pre-formed organic molecules as their source of both carbon and energy.
Fungi are extremely diverse and their unique life-history strategies allow them to serve a wide variety of ecological roles, for example decomposers, mutualists, endophytes of plants, pathogens, and even predators (Wall, A.; 1999). Fungal hyphae are foundational components of soil food webs because they are forage for grazing soil biota. Fungalsporocarps are also important foods for larger animals. While fungi perform a vast diversity of functions, some functional groups of fungi have particular importance in soil ecosystems: the saprotrophs, the mycorrhizas (lindahl, R.; 2001). The saprotrophic fungi produce a wide range enzymes, including amylases, protease, lipases, and phosphatases. These enzymes are produced by hyphae at the front of the mycelium as it grows through its substrate. Saprotrophic fungi increase the biomass and diversity of soils and play a critical role in decomposition.
The mycorrhizal fungi form mutual beneficial symbiotic associations with living plant roots. The symbiosis is based on the exchange of resources: the plant receives soil nutrients from the fungus and the plant provides sugar as a source of carbon to the fungus.
1.4 AIMS AND OBJECTIVES OF THE STUDY
The present study was carried out to:
- To isolate and enumerate the different species of fungi found in potting soil.
- To determine the fungal load of potting soil.
- To assess and compare the composition, abundance and diversity of fungi in selected potting soil samples.
- To compare the diversity of fungi in potting soil and in control soil.
1.5 LITERATURE REVIEW
1.5.1 DIVERSITY OF FUNGI
Microorganisms are frequently present in soil, manure and decaying plant tissues (Alexander, 1997). Agriculture soil is a dynamic medium in which a large number of pathogenic and non-pathogenic fungal floras live in close association. Microbes in the soil are the key to carbon and nitrogen recycling. Microorganisms produce some useful compounds, which are beneficial to soil health, plant growth and play an important role in nutritional chains that are important part of the biological balance in the life in our plant (Paul and Clerk; 1966, Kummerer, 2004).
Some fungi are very harmful causing food spoilage and diseases to plants, animals and humans with different significant economic losses and produce mycotoxins in certain products (Manoch, 1998). There are about 75,000 species of soil fungi in the world (Finlay, 2007) but in Thailand, soil fungi, identified until 1998, numbered only 89 genera and 95 species (Manoch, 2004). Many studies of soil fungi in Thailand in the past emphasized species diversity in soil ample collected from various agricultural areas and forest types (Manoch, 1993, 1998: Kosol, 1999; Manoch etal., 2000; Dethoup et al., 2007). However, relatively few studies have made efforts to compare quantitatively the fungal diversity among different habitats.
On the other hand, some fungi play a vital role as major decomposers in the soil ecosystem. They also provide mankind with very useful pharmaceutical products such as antibiotics and other valuable substances including organic acids, enzymes, pigments and secondary metabolites used in food industry and fermentation. In addition, many soil fungi are biological control agents for plant pathogens and insect pests.
There have been also very few studies on the relationships of soil fungal diversity with environmental factors. Wongseenin, (1971) reported that the soil fungal population and diversity were higher in the dry evergreen forest than in the dry dipterocarp forest on the Sakaerat Environmental research station, Nakhon Ratchasima province. These higher numbers corresponded with the higher moisture content, organic matter content, mineral levels and acidity of soil in the former type than in the latter (current) one.
Wongvuti, Y. (1993) compared the number of microorganisms (fungi and bacteria) in disturbed natural forest and in undisturbed forest following selection cutting in Kanchanaburi province and found out that two years after the cutting, there was no difference in the numbers of microorganisms between the two sites, because there had not been enough time for disturbance to change the environments of the microorganisms.
However, three years after the cutting, the number of microorganisms in the disturbed site showed a decreasing trend, as the soil that had a higher PH and lower organic matter and mineral P than the undisturbed natural forest soil. Since forest soil microbial biomass is dominated by fungi (Houston et al. 1998), studying fungal diversity in relation to soil properties may provide useful information on soil fungal diversity management of the areas.
1.5.2 POTTING SOIL
Potting soil is also known as potting mix or potting compost, this potting soil is a medium in which plants, herbs, and vegetables are grown in pots or other durable containers. (Dighton, J., et al; 1997)
Most potting soil seen in a garden center are comprised of three basic ingredients; which are Peat Mass, Pine Bark, and either Perlite or Vermiculite. (To provide air space). (Dighton j., et al; 1997)
Peat Moss comes from the peat bags of the northern United States and Canada: this peat moss provides a great moisture retaining quality with good air space for healthy growing roots. This is sometimes the very best potting mix. However, for most flowering annuals peat moss by its self is too acidic, so it is usually best to go with a blended potting mix that has all the three ingredients in it. When making use of peat moss as your potting mix, be careful not to over water it because peat moss all by itself can stay wet for long period of time after watering.
Note:A bag of straight peat moss that is very dry is said to repel water. In this situation, the best thing to do is soak the peat moss either in a bag, in wheel barrow or bucket. Usually soaking it overnight will get things well saturated and then it can be easier to use. (Filion Cassel, D.K., &Wollum, A.G., 1999)
Once it has been saturated, it will also go back to the state of retaining water with no further issues.
Pine bark comes from paper mills all over the United States and Canada. It acts to provide some moisture and fertilizer retention; and also a bit more air space. All by itself, pine back does not provide enough of anything to really support plant life, but once it is mixed with peat moss.
Pine bark adds a new dimension and helps to extend the “life” of the potting mix by being relatively slow to break down.
Perlite and vermiculite are both volcanic in origin and both are put into potting mix to provide additional air space and to lighten up the potting mix so that it won’t be too dense and heavy. Perlite does not provide any nutritional benefit and can collect fluoride in water containing it. That means the fluoride concentrates for a while and can bum the leaf tips of some house plants like Dracaena and Spider plant.(Chlorophytum).Vermiculite is a bit different in the sense that it holds a lot of moisture and can also hold onto fertilizer for a period of time, helping to keep nutrients around the roots of the plants instead of washing out the bottom of the pot.
In summary, Peat Mossprovides moisture and nutrient retention, Pine bark provides anchorage; some nutrient and moisture retention and air space; Perlite and Vermiculiteprovide most of the air space in the soil. (Filion Cassel, D.K., &Wollum, A.G., 1999)
The diversity of physical characteristic of soil associate with aggregation at small scales means that soil can contain a large diversity of microorganisms in close proximity and the chemical composition of soil is also highlyheterogeneous in both vertical and horizontal dimensions (Dighton et al., 1997, Gallant et al.,). Potting soil is a collective name for various kinds of soil with each of their own composition and specific structure especially plants in pots and flower boxes.
Potting soil is light in weight, unlike the other soils; for example the heavier dark garden soil. Potting soil is a common medium used in gardening because it is convenient to use. In addition, potting soil consists of amendments and nutrients needed for plants to thrive.
The physical properties of potting soil includes water holding capacity, aeration, plasticity, texture, structure, density and colour. While the chemical composition of potting soil refer to its mineralogical composition.
Soil fungi lay pivotal roles in various biogeochemical cycle (BGC) (Motin, 1997;Trever’s, 1998), and are responsible for the cycling of organic compounds. Soil microorganisms also influence above-ground ecosystems by contributing to plants nutrition (George etal., 1995, Timonen et al., 1996), plant health (Srivastavaet al., 1996, Filion et al.,1999, Smith and Goodman, 1999), soil structure (Wright and Upadhyaya, 1998, Dodd et al., 2000), and soil fertility (Yao et al., 2000, O’Donnell et al ., 2001) our knowledge of soil microbial diversity is limited in part by our in ability to study soil microorganisms.
1.5.3 FUNGAL GROWTH ON POTTING SOIL
Most prepared soils that are bagged and sold at garden centers and home supply stores have been presumed to be prepared months in advance of the actual sale. Normally, these mixed soils are composed, sterilized or at least heat-treated to eliminate any of diseases, weed seeds and other pathogens that could ultimately impact or invade on what you are going to pot and grow in the soil. When you break open the bag and use the mix, you are exposing the sterile soil to a huge assortment of native fungi spores that are ambient in your home or garden. The sterile soil is a perfect home for these fungi since there is no competition for the organic material that makes up the soil mix. These fungi grow fast especially when given the ideal growing conditions (Which seem to be identical to those conditions we want to grow our new spring plants in). Under normal outdoor growing conditions the fungi are usually short lived.
Drying the soil mix out, exposure to sunlight and simply being exposed to other competitive organisms, the mildews disappear through rapid attrition.
Most of the time, the appearance of these mildews that grow on the soil means absolutely nothing to the health of the plants being planted in the soil. Other than an indicator that perhaps the soil is too moist or has too much organic material in it.For the mildew issue to be eliminated, the bag should be opened a few days before used and spread out on a sheet or cloth, exposed to sunlight and the re-bag or put it into a soil bin when it is dry. The soil can be used without worry either fresh out of the bag or “conditional and dried”.
Fungi are microscopic cells that usually grow as long threads or strands called hyphae, which push their way between soil particles.
Hyphae are usually a few micrometer in diameter. Single hyphae can span in length from a few cells to many yards. A few fungi such as yeast are single cells. Hyphae sometimes group into masses called mycelium or thick, cord-like “rhizormorphs” that look like roots. Fungal fruiting structures (mush-rooms) are made of hyphal strands. (Strivastava, et al., 1993)
Fungi in soil are present as Mycelial bits, Rhizomorphor as different spores. Their number varies from a few thousand to a few million per gram of soil. Soil fungi possess filamentous mycelium composed of individual hyphae. The fungal hyphae may be Aseptate(Mastigomycotina and Zygomycotina) or Septate (Ascomycotina, Basidiomycotina and Deuteromycotina). Most commonly encountered genera of fungi in soil are; Aspergillus, Cladosporuim, Chaetomium, Mucor, Penicillium, Verticillium, Rhizopus, Monilia, Pythium, etc. most of these fungal genera belong to a Subdivision Deuteromycotina/Fungalimperteactawhich lacks the sexual mode of reproduction.(Yao, K., D. Halm, et al., 2000)
As these soil fungi are aerobic and heterotrophic, they require abundant supply of oxygen and organic matter in the soil, because acidic environment is not conducive for their existence. Soil fungi can be grouped in to three general functional groups based on how they get their energy. These groups are;
Saprophytic Fungi They concert dead organic materials into fungal biomass, carbon di oxide (CO2), these fungi generally use complex substrates, such as cellulose, and lignin, in woods, and are essential in decomposing the carbon ring structures in some pollutants. Fungi are important for immobilizing or retaining nutrients in the soil.
The Mycorrhizal fungi: They colonize plant roots. In exchange for carbon from plant, Mycorrhizal fungi help to solubilize phosphorus and bring soil nutrients such as (phosphorus, nitrogen, micronutrients and perhaps water) to the plant. One major group of Mycorrhizae is the Ectomycorrhizaethat grows on the surface layer of the roots and is commonly associated with trees. The second major group of Mycorrhizae is the Endo Mycorrhizaein the sense that they grow within the root cells and are associated with grasses, row crops, vegetables and shrubs.
Pathogens and Parasites
They are the third group of fungi in soil. They cause reduced production or death when they colonize roots and other organisms. Many fungi help control diseases. For example, nematode-trapping fungi that parasitize disease-causing nematodes, and fungi that feed on insects may be useful as bio control agents. Many plants depend on fungi to help extract nutrient from soil.
1.5.4 ROLES OF FUNGI IN SOIL
- Fungi play significant role in soils and plant nutrition.
- They play important role in boil aggregation and in the formation of humus.
- They play important role in the degradation/decomposition of cellulose, hemi cellulose, starch, pectin, lignin in the organic matter added to the soil.
- Fungi decomposes lignin is resistant to decomposition by bacteria.
- Fungi serve as food to bacteria.
- Some soil fungi are parasitic and cause number of plant diseases such as wilts, root rots, damping off and seedling blights e.g. Pytlium, Fusarium, Vertialluim etc.
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