Soil microflora (0)

Estonian University of Life Sciences
Report on
Soil Microflora
By Katrin Vares
Tartu 2013

Contents

Introduction 3
Definition , composition and importance of microflora 3
Factors influencing soil microflora 4
Natural conditions 4
Cultural practices 5
Conclusion 6
Bibliography 6
Definitions 7
Factors incluencing soil microflora 8

Introduction

The purpose of this report is to define soil microflora and establish the importance of it. Since the microorganisms clearly play an important role in preserving the balance of life, the next objective is to look into factors that influence this balance. Natural conditions and cultural impact could be considered as the variables that correlate the most with the activity and composition of microflora, hence some of the natural and cultural factors will be looked into a little more in detail.

Definition, composition and importance of microflora

Saunders Comprehensive Veterinary Dictionary (2007) cited by the online medical dictionary (2013) defines living microorganisms as that small that they can be seen only with a microscope and that maintain a more or less constant presence in a particular area that includes bacteria , viruses, protozoa and fungi. Soil microflora more specifically, consists the following microorganisms ( Bhatt et al. 2013):

Bacteria

Heterotrophic bacteria, eg. symbiotic and non - symbiotic N2 fixers, ammonifier, cellulose decomposers , denitrifiers

Autrotrophic bacteria, eg. nitrosomonas, nitrobacter, sulphur oxidizers, etc;

Fungus;

Viruses

Actinomycetes and stretomyces;

Algae eg. BGA, yellow gree algae, golden brown algae.
The soil microflora largely depends on the type of soil, temperature, moisture, plant growth , nutrients, pH, and many other factors which may vary between locations but also within a single plot and over very small distances ( OECD , 2007). Nevertheless of the quantity of microflora, biomass of all microorganisms living in soil play an important role in the functioning of entire soil ecosystems because their enormous biochemical activity (Barabasz et al. 2002).
Soil microflora cycles carbon , nitrogen, phosphorus , and sulfur , plays a role in soil structure formation , decomposition of organic matter , toxin removal, promoting plant growth, and in changes in vegetation (Canbolat at al. 2005 and Martin et al. 2012). Therefore , soil microflora plays a major role in preservation and the balance of life. Because of active role of soil micro-population, the diminution in microbial activity is always alarming (Barabasz et al. 2002).

Factors influencing soil microflora

Soil microorganisms depend on soil for their nutrition, growth and activity. Based on My Agriculture Information Bank (2013) the major soil factors which influence the microbial population, distribution and their activity in the soil are:

Natural conditions ( including soil fertility, pH, aeritation, temperature, moisture, organic matter, food and energy supply, microbial association and interactions)

Cultural practices
These factors play a great role in determining not only the number and type of organism but also their activities . Variations in any one or more of these factors may lead to the changes in the activity of the organisms which ultimately affect the soil fertility level.

Natural conditions

Extreme environments such as high-altitude and highlatitude ecosystems are very sensitive to environmental changes. Global warming is hypothesised to alter both above - and below ground processes affecting the soil ecosystem ( Asher et al. 2012). As an example, Asher et al. (2012) further proved in their research on humus creation that thermal conditions (due to differences in altitude and exposure ) and consequently the climate influence soil microflora considerably. Humus being defined as an organic residue in the soil resulting from decomposition of plant and animal residues in soil, or it is the highly complex organic residual matter in soil which is not readily degraded by microorganism (Kausadikari).
There are several other variables that impact the soil microflora. For instance , a study by Canbolat et al. (2007) showed that root length, root and shoot weight of plants were decreased by soil compaction, which suggests that microfloral activity in compact soil is lower .

Cultural practices

The mankind has and will have a major influence on changing the microflora of soils. There are countless activites that have and minor effect , but change the soil composition in the long term as a whole . Although, some activites like agriculture, waste management and forestry carried out to satisfy the needs of the people have major impact on in areas of action .
Sidorenko and Buzoleva (2007) stated that soil microbiocenosis is one of the most complicated biological communities. Various interrelationships occur between bacteria in the process of their activity, including those at the metabolic level. These interralationships can will bias the balanced system. For instance, Halasz et al. (2011) researched clearly showed that soils, degradation and transformation of natural and xenobiotics depends on the activities of soil enzymes and the number and activities of soil micro organisms. Deposited waste of dumps as an ecological factor changes the chemical composition, microflora and enzyme activity of soils.
Agriculture and fertilisation of soil is another mojor game changer for the microflora of soil. Canbolat et al. (2007) state in their research that microbial biomass appeared to increase with both mineral fertilization and bacterial inoculation, whereas the microbial community structure ( total culturable bacteria and fungi) changed consistently according to the treatments applied. As another example, Lipsa (2011) claimes that his results show that the compost applied on maize fields has in general, a positive influence on soil microflora structure and biological activity, which can be compared with the mineral elements influence. Furthermore, with the same research on maiz, he states that the highest number of microorganisms/g soil was recorded in the variant fertilized with N150P75K75, while not saying that the influence was positive.

Conclusion

The topic of soil microflora is wide and it is rather hard to grasp the essental information without going into detail. Nevertheless, the report has identified the microorganisms in the biomass as being different types of bacteria, fungus, viruses and types of algae. These microorganisms are interdependent at many times and the amount of them can be influences by many variable that range from climatial to mankind.

Bibliography

Ascher, J., Sartori, G., Graefe, U., Thornton, B., Ceccherini, M. T., Pietramellara, G., & Egli, M. (2012). Are humus forms , mesofauna and microflora in subalpine forest soils sensitive to thermal conditions? Biology and Fertility of Soils, 48(6), 709–725. doi:10.1007/s00374-012-0670-9
Barabasz, W., Albińska, D., Jaśkowska, M., Lipiec, J., 2002 - Biological effects of mineral nitrogen fertilization on soil microorganisms, Polish Journal of Environmental Studies , vol. 11, No. 3, p. 193-198.
Canbolat, M. Y., Bilen, S., Çakmakçı, R., Şahin, F., & Aydın, A. (2005). Effect of plant growth-promoting bacteria and soil compaction on barley seedling growth, nutrient uptake, soil properties and rhizosphere microflora. Biology and Fertility of Soils, 42(4), 350–357. doi:10.1007/s00374-005-0034-9
Halász, J. L., Kotroczo, Z., Krausz, E., Tóth, M. D., & Balázsy, S. (2011). EFFECT OF POLLUTION IN THE FLORA , MICROFLORA AND SOIL ENzYME ACTIVITIES NEAR TO THE UPPER -TISzA, 21(4), 803–811.
Kausadikar, H. K., & Ssac, A. O. F. (n.d.). Definition of Soil Microbiology & soil in view of Microbiology Rajan Bhatt, Krishi Vigyan Kendra , Kapurthala (Punjab). http://www.scribd.com/doc/27429437/Soil-Microbiology
Lipşa, F. D. (n.d.). INVESTIGATIONS ON THE INFLUENCE OF FERTILIZATION AND MAIZE ( ZEA MAYS L .) ROOT EXUDATES ON SOIL MICROFLORA.
Martin, G., Guggiari, M., Bravo, D., Zopfi, J., Cailleau, G., Aragno, M., Job, D., et al. (2012). Fungi, bacteria and soil pH: the oxalate-carbonate pathway as a model for metabolic interaction. Environmental microbiology, 14(11), 2960–70. doi:10. 1111 /j.1462- 2920 .2012.02862.x
My Agriculture Information Bank. Retreived 13 March 2013. http://agriinfo.in/?page=topic&superid=5&topicid=152
OECD.2007. Consensus Document on Safety Information on Transgenic Plants Expressing Bacillus thuringiensis - Derived Insect Control Protein . ENV/JM/ MONO (2007) 14. Series on Harmonisation of Regulatory Oversight in Biotechnology. http://www.agbios.com/docroot/articles/07-214-001.pdf
Saunders Comprehensive Veterinary Dictionary (2007). Retrieved March 13 2013 from http://medical-dictionary.thefreedictionary.com/microflora .
Sidorenko, M. L., & Buzoleva, L. S. (2008). Character of interactions of saprophytic soil microflora via gaseous metabolites. Microbiology, 77(2), 235–239. doi:10.1134/S0026261708020185

Definitions

Heterotrophic bacteria - bacteria that use organic (carbon-containing) compounds as a source of energy and carbon. This characteristic distinguishes heterotrophic bacteria from chemoautotrophic (chemosynthesizing) and photoautotrophic (photosynthesizing) bacteria, which assimilate CO2 as a source of carbon. The overwhelming number of known species of bacteria, both aerobic and anaerobic , are heterotrophic. Many heterotrophic bacteria utilize sugar, alcohol , and organic acids. However , there are specialized heterotrophic bacteria capable also of decomposing cellulose, lignin, chitin, keratin, hydrocarbons, phenol, and other substances. Heterotrophic bacteria take an active part in the natural recycling of substances.
Autrotrophic bacteria – Autotrophic bacteria make their own food, either by photosynthesis (which uses sunlight, carbon dioxide and water to make food) or by chemosynthesis (which uses carbon dioxide, water and chemicals like ammonia to make food - these bacteria are called nitrogen fixers and include the bacteria found living in legume roots and in ocean vents).
Fungi - is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds ( British English : moulds), as well as the more familiar mushrooms.
Actinomycetes - any member of a heterogeneous group of gram -positive, generally anaerobic bacteria noted for a filamentous and branching growth pattern that results, in most forms, in an extensive colony , or mycelium. The mycelium in some species may break apart to form rod- or coccoid-shaped forms. Many genera also form spores; the sporangia, or spore cases , may be found on aerial hyphae, on the colony surface, or free within the environment. Motility, when present , is conferred by flagella. Many species of actinomycetes occur in soil and are harmless to animals and higher plants, while some are important pathogens, and many others are beneficial sources of antibiotics.
Stretomyces - Over 500 species of Streptomyces bacteria have been described . As with the other Actinobacteria, streptomycetes are Gram-positive, and have genomes with high GC content. Found predominantly in soil and decaying vegetation, most streptomycetes produce spores, and are noted for their distinct "earthy" odor that results from production of a volatile metabolite, geosmin.
Algae - any of numerous groups of chlorophyll-containing, mainly aquatic eukaryotic organisms ranging from microscopic single-celled forms to multicellular forms 100 feet (30 meters) or more long, distinguished from plants by the absence of true roots, stems, and leaves and by a lack of nonreproductive cells in the reproductive structures. Today , algae are used by humans in many ways ; for example, as fertilizers, soil conditioners and livestock feed.[54] Aquatic and microscopic species are cultured in clear tanks or ponds and are either harvested or used to treat effluents pumped through the ponds. Algaculture on a large scale is an important type of aquaculture in some places . Maerl is commonly used as a soil conditioner.

Factors incluencing soil microflora

1. Cultural practices ( Tillage ):Cultural practices viz. cultivation, crop rotation , application of manures and fertilizers, liming and gypsum application, pesticide/fungicide and weedicide application have their effect on soil organism. Ploughing and tillage operations facilitate aeration in soil and exposure of soil to sunshine and thereby increase the biological activity of organisms, particularly of bacteria. Crop rotation with legume maintains the favorable microbial population balance, particularly of N2 fixing bacteria and thereby improve soil fertility.
Liming of acid soils increases activity of bacteria and actinomycetes and lowers the fungal population. Fertilizers and manures applied to the soil for increased crop production, supply food and nutrition not only to the crops but also to microorganisms in soil and thereby proliferate the activity of microbes.
Foliar or soil application of different chemicals (pesticides, fungicides, nematicides etc.) in agriculture are either degraded by the soil organisms or are liable to leave toxic residues in soil which are hazardous to cause profound reduction in the normal microbial activity in the soil.
2. Soil fertility: Fertility level of the soil has a great influence on the microbial population and their activity in soil. The availability of N, P and K required for plants as well as microbes in soil determines the fertility level of soil. On the other hand soil micro flora has greater influence on the soil fertility level.
3. Soil moisture: It is one of the important factors influencing the microbial population & their activity in soil. Water (soil moisture) is useful to the microorganisms in two ways i.e. it serve as source of nutrients and supplies hydrogen / oxygen to the organisms and it serve as solvent and carrier of other food nutrients to the microorganisms. Microbial activity & population proliferate best in the moisture range of 20% to 60%. Under excess moisture conditions / water logged conditions due to lack of soil aeration (Oxygen) anaerobic microflora become active and the aerobes get suppressed. While in the absence of adequate moisture in soil, some of microbes die out due to tissue dehydration and some of them change their forms into resting stages spores or cysts and tide over adverse conditions. Therefore optimum soil moisture (range 20 to 60 %) must be there for better population and activity of microbes in soil.
4. Soil temperature: Next to moisture, temperature is the most important environmental factor influencing the biological physical & chemical processes and of microbes, microbial activity and population in soil. Though microorganisms can tolerate extreme temperature (such as - 60 ° or + 60 u) conditions, but the optimum temperature range at which soil microorganisms can grow and function actively is rather narrow.
Depending upon the temperature range at which microorganisms can grow and function, are divided into three groups i.e. psychrophiles ( growing at low temperature below 10 °C) Mesophiles (growing well in the temp range of 20 ° C to 45° C) and thermopiles (can tolerate temperature above 45° C and optimum 45-60°C).
Most of the soil microorganisms are mesophilic (25 to 40 °) and optimum temperature for most mesophiles is 37° C. True psychrophiles are almost absent in soil, and thermopiles though present in soil behaves like mesophiles. True thermopiles are more abundant in decaying manure and compost heaps where high temperature prevails.
Seasonal changes in soil temperature affect microbial population and their activity especially in temperate regions . In winter, when temperature is low (below 50° C ), the number and activity of microorganisms falls down, and as the soils warms up in spring , they increases in number as well as activity. In general, population and activities of soil microorganisms are the highest in spring and lowest in winter season .
5. Soil air (Aeration): For the growth of microorganisms better aeration (oxygen and sometimes CO2) in the soil is essential. Microbes consume oxygen from soil air and gives out carbon dioxide. Activities of soil microbes is often measured in terms of the amount of oxygen absorbed or amount of Co2 evolved by the organisms in the soil environment. Under high soil moisture level / water logged conditions, gaseous exchange is hindered and the accumulation of Co4 occurs in soil air which is toxic to microbes. Depending upon oxygen requirements , soil microorganisms are grouped into categories viz aerobic ( require oxygen for like processes), anaerobic (do not require oxygen) and microaerophilic (requiring low concentration / level of oxygen).
6. Light: Direct sunlight is highly injurious to most of the microorganisms except algae. Therefore upper portion of the surface soil a centimeter or less is usually sterile or devoid of microorganisms. Effect of sunlight is due to heating and increase in temperature (More than 45°)
7. Soil Reaction / Soil PH: Soil reaction has a definite influence / effect on quantitative and qualitative composite on of soil microbes. Most of the soil bacteria, blue -green algae, diatoms and protozoa prefer a neutral or slightly alkaline reaction between PH 4.5 and 8.0 and fungi grow in acidic reaction between PH 4.5 and 6.5 while actinomycetes prefer slightly alkaline soil reactions. Soil reactions also influence the type of the bacteria present in soil. For example nitrifying bacteria (Nitrosomonas & Nitrobacter) and diazotrophs like Azotobacter are absent totally or inactive in acid soils, while diazotrophs like Beijerinckia, Derxia, and sulphur oxidizing bacteria like Thiobacillus thiooxidans are active in acidic soils.
8. Soil Organic Matter: The organic matter in soil being the chief source of energy and food for most of the soil organisms, it has great influence on the microbial population. Organic matter influence directly or indirectly on the population and activity of soil microorganisms. It influences the structure and texture of soil and thereby activity of the microorganisms.
9. Food and energy supply: Almost all microorganisms obtain their food and energy from the plant residues or organic matter / substances added to the soil. Energy is required for the metabolic activities of microorganisms. The heterotrophs utilize the energy liberated during the oxidation of complex organic compounds in soil, while autotrophs meet their energy requirement form oxidation of simple inorganic compounds (chemoautotroph) or from solar radiation (Photoautotroph). Thus, the source of food and energy rich material is essential for the microbial activity in soil. The organic matter, therefore serves both as a source of food nutrients as well as energy required by the soil organisms.
10. Nature of Soil: The physical, chemical and physico-chemical nature of soil and its nutrient status influence the microbial population both quantitatively and qualitatively. The chemical nature of soil has considerable effect on microbial population in soil. The soils in good physical condition have better aeration and moisture content which is essential for optimum microbial activity. Similarly nutrients (macro and micro) and organic constituents of humus are responsible for absence or presence of certain type of microorganisms and their activity. For example activity and presence of nitrogen fixing bacteria is greatly influenced by the availability of molybdenum and absence of available phosphate restricts the growth of Azotobacter.
11. Microbial associations / interactions: Microorganisms interact with each other giving rise to antagonistic or symbiotic interactions. The association existing between one organism and another whether of symbiotic or antagonistic influences the population and activity of soil microbes to a great extent. The predatory habit of protozoa and some mycobacteria which feed on bacteria may suppress or eliminate certain bacteria. On the other hand, the activities of some of the microorganisms are beneficial to each other. For instance organic acids liberated by fungi, increase in oxygen by the activity of algae, change in soil reaction etc. favors the activity or bacteria and other organisms in soil.
12. Root Exudates: In the soil where plants are growing the root exudates also affects the distribution, density and activity of soil microorganism. Root exudates and sloughed off material of root surfaces provide an abundant source of energy and nutrients and thus directly or indirectly influence the quality as well as quantity of microorganisms in the rhizosphere region . Root exudates contain sugars, organic acids, amino acids, sterols, vitamins and other growth factors which have the profound effect on soil microbes.