SOIL MICROBIOLOGY and microflora in soil

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1. SOIL MICROBIOLOGY IMPORTANCE OF MICROFLORA OF SOIL Roselin Angel A ( 24PBO111 )

2. CONTENTS INTRODUCTION SOIL AS NATURAL MEDIUM DISTRIBUTION OF MICROBES IN SOIL SOIL MICROORGANISMS MICROFLORA IN SOIL ROL E OF MICROFLORA IN SOIL

3. INTRODUCTION Soil microbiology is a study of various microbes present in the soil , their function and their impact on the soil. Sergei Winogradsky is considered as Father of Soil Microbiology. Soil contains various microorganisms such as bacteria, fungi, virus, blue-green algae, actinomycetes, protozoa, and nematodes. Soil microorganism are present in high numbers and have a range of metabolic activities and also play a vital role in nutrient cycling.

4. Soil as a natural medium Soil acts as a medium that supports the growth of wide range of microorganisms. Soil contains nutrients, organic matter, and ions like Na+, K+, Mg++, Ca++, Fe ++, S-, Po4-, No3-,etc,. Soil is not a static medium, it is a constantly changing medium. One gram of soil contains : As many as one billion bacteria Hundred million actinomycetes One million fungi 100 nematodes

5. Distribution of microbes in soil Microorganism constitute <0.5% of the soil mass, yet the have major impact on soil properties. The distribution of microorganism in soil differ from one area of soil to another. The rhizosphere harbors more microorganism than other parts of the soil. Because plant root release a variety of compounds that support higher microbial populations.

6. Microorganisms found not only in surface soil but also in subsurface soil at depths ranging from 100s to 1000sof meters below the ground.
Generally, the number of microorganisms declines with increasing depth in the soil profile, primarily due to decreases in soil organic matter content

7. Soil microorganisms Microorganisms in soil can be grouped on the basis of their size, species type and function. The major group of microorganisms in the soil are : Bacteria Actinomycetes Fungi Algae Protozoa Nematodes

8. Bacteria Bacteria are prokaryotic, unicellular microorganism. Size range from 0.5 to 1 micrometre. Various shapes of bacteria including rod, spherical, spiral and filamentous forms are present. Bacterial bio mass found in soil ranges from 300 to 300 kg/ha. Bacteria present abundantly in the rhizosphere region which host large number of gram negative and denitrifying bacteria. Bacteria do not occur freely in the soil solution but are closely attached to the soil particles are embedded in organic matter.

9. Bacteria in soil Some of the bacteria present in the soil includes Bacillus, Arthrobacter , Clostridium, Corynebacterium , Nitrosomonas , Nitrobacter , Pseudomonas, Rhizobium , etc ,

10. Actinomycetes Actinomycetes commonly called as ray fungi. They are filamentous, gram positive bacteria more abundant in alkaline soil. Actinomycetes are mostly anaerobic that form either colonies for extensive mycelia Size ranges between 0.5 to 1.5 micrometer . Optimum Ph ranges from 6.5 – 8.0 The earthy odour of newly wetted soil due to the presences of actinomycetes. Examples: actinomyces, streptomyces, micromonospora , nocardia, actinoplanes , thermoactinomyces , etc.

11. Actinomycetes

12. Fungi Fungi are eukaryotic organisms, which can be unicellular, but often multicelluar . Fungus usually grow as long threads or strands called hyphae .network called mycelia which penetrates soli giving crumb nature. Biomass of fungi ranges from 500 to 5000 kg/ha. Majority of soil fungi grow in acidic soils with aerobic condition. Fungi may be parasitic, saprophytic and symbiotic. Some of the soil fungi includes, mucor, penicillium, aspergillus, fusarium ,phytopthora, verticillium, Pythium, rhizoctonia etc.

13. ALGAE Algae are photosynthetic, eukaryotic organisms. Algae are photosynthetic organisms. Generally found on the surface of moist soils.so they are found near upper layer or just below the surface layer of soil. Examples of soil algae: green algae ( Chlamydomonas, chlorella, cladophora , coccomyxa ) , yellow green algae ( heteroccocus , heterothrix , botrydiopsis ) diatoms( navicular,pinnularia , Fragilaria), blue green algae ( nostoc , Oscillatoria,anabaena )

14. Algae

15. PROTOZOA Protozoa are unicellular, eukaryotic microorganisms. Larger than bacteria, varying from few microns to few millimeters . They are motile heterotrophs obtain food by ingesting bacteria, yeasts, algae and organic matter. Some form symbiotic relationship. Flagellate and amoeba type of protozoa are usually abundant in soil. Protozoans may exist as vegetative or cyst form.. Examples: cercomonas , spiromonas , Chlamydomonas, euglena, biomyxa,lecythium,trinema , colpidium , vorticella, gastrostyla .

16. Protozoa

17. Nematodes Nematodes are small, microscopic worm like microorganisms. Nematodes derives it nutrition for their growth and reproduction from the cell contents of protozoa , bacteria, fungi. Some of the soil nematode include pleuritricha , heteromita,colpoda etc

18. Microbial flora of soil Soil microflora refers to group of soil microorganisms , which primarily constitute the portion of the soil organic matter and some colloidal portion of soil humus. Soil microflora includes microbes like fungi, bacteria, actinomycetes, algae, protozoa etc. Soil microflora contributes to the biological property of soil. The physical and chemical factors like Ph , temperature, available moisture, and nutrients influence the growth and activity of soil microflora.

19. Importance of soil microflora in soil Soil microflora has a significant role in promoting soil and plant health. The microorganisms present in the soil interacting with the biotic components of ecosystem , including plants, animals and humans. The soil microflora plays a vital role by participating in various soil transformation processes like weathering of rocks, breakdown of organic matter, and nutrient recycling. Therefore soil microorganisms represent a large fraction of global biodiversity. Various role of microbes in the soil are as follows,

20. Role Of Bacteria In Soil Decomposition of organic matter. Conversion of soil constituents into material useful for plant life. produce polysaccharides or glycoproteins which act as cementing agents and improve soil structure. Biogeochemical cycling of elements like carbon, nitrogen, phosphorus,iron , sulphur, manganese. Act as indicators of soil.

21. Role of fungi Improves the water holding capacity of soil Saprophytic fungi participate in formation of humus by degrading plant and animal remains. Produces a wide range of antibiotics Certain fungi produce growth promoting substances for host plant( fusarium produces gibberellic acid). Help to trap nematodes ( Arthrobotrys conoides ) Forms symbiotic association roots of higher plants – Mycorrhizae Lichens are symbiotic associations of fungi and algae .act as important soil colonizers.

22. Mycorrhizal association

23. Role of Algae They generate organic matter by photosynthesis Maintaining the soil fertility. Helps in fixing nitrogen in soil . Used as biofertilizers BGA play a key role in transformation of rock into soil. They have ability to corrode and weather rocks. Preventing soil erosion.

24. Role of Actinomycetes Plays a vital role in degrading more resistant organic substances. Important in agricultural soils as they increase the soil fertility through nutrient cycling. Form associations with non – leguminous plants and fixes Nitrogen. Produces antibiotics (streptomycin)

25. Role of protozoa Act as bacterial consumers. Thus regulate the bacterial population in soil contributing to biological equilibrium. Enhances the nutrient cycle and energy flow between microbes, plants and animals. Act as bioindicators.

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