Soil Microbiology Ambarish Bhuyan Assistant Professor Botany Department MDKG College, Dibrugarh
INTRODUCTION Nature of soils Soil arises from the weathering of rocks Soil also produced through the actions of microorganisms
Topsoil Subsoil Organics, nutrients Decrease with depth Numbers of microorganisms Decrease with depth but still present in bedrock Bedrock
Soil Microbiology Environmental factors affecting microbial abundance in soils Moisture content Moist soils support microbial growth better than dry soils Oxygen ph Moist soils are lower in oxygen than dry soil Highly acidic and highly basic soils favor fungi
Temperature Most soil organisms are mesophiles Nutrient availability Microbial community size determined by how much organic material is available
Microbial populations in soils Bacteria Archaea Virus Fungi Algae and protozoa Microbes perform a number of functions Cycle elements and convert them to usable form Degrade dead organisms Produce compounds with potential human uses
Role of Microorganisms in Biogeochemical Cycles Biogeochemical cycles Processes by which organisms convert elements from one form to another Elements often converted between oxidized and reduced forms Involve the recycling of elements by organisms
Biogeochemical cycling entails three processes Production Inorganic compounds converted into organic compounds Consumption Organisms feed on producers and other consumers Decomposition Organic compounds in dead organisms converted into inorganic compounds
NITROGEN CYCLE
Proteins and waste products Microbial decomposition Amino acids Amino acids ( NH 2 ) Microbial ammonification Ammonia (NH 3 ) Ammonium ion (NH 4+ ) Nitrosomonas Nitrite ion (NO 2 ) Nitrite ion (NO 2 ) Nitrobacter Nitrate ion (NO 3 ) Nitrate ion (NO 3 ) Pseudomonas N 2 N 2 Nitrogen fixation Ammonia (NH 3 )
Root Root hairs Nodules Rhizobia attach to root hair. Bacteroids Enlarged root cells form a nodule. Infection thread Rhizobia Bacteria change into bacteroids; packed root cells enlarge. An infection thread is formed, through which bacteria enter root cells.
Mycorrhiza Mutualistic symbiosis (non-pathogenic association) between soil-borne fungi and roots of plants. Greek: mykes (mushroom) and rhiza (root) (Frank, 1885)
Types of mycorrhiza Ectomycorrhiza The fungus grows intercellularly (never intracellularly) in the cortex of plant s root Endomycorrhiza The fungus grows inter- and intracellularly and forms specific fungal structures within the cortical cells. Vesicular Arbuscular Mycorrhiza (Arbuscular Mycorrhiza) Ericoid Mycorrhiza Orchid Mycorrhiza
Importance of Mycorrhiza Increase the soil volume explore for nutrient upatake Enhance the efficiency of nutrient absorption from the soil solution Improved uptake of soil phosphorus Mycorrhizal plants are more resistant to many root diseases Mycorrhizal plants are often more drought tolerant
References Dubey R.C. and Maheshwari D.K. A Textbook of Microbiology ; Second revised edition; S.Chand publication. Black J.G. Microbiology ; Seventh Edition; Wiley publication. Sharma P.D. Microbiology and Plant Pathology, second edition; Rastogi Publication. Vashishta B.R. And Sinha A.K. Botany for degree students- fungi, revised edition; S.Chand publication
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AGARICUS PRESENTED BY- Ambarish Bhuyan Assistant Professor Botany Department MDKG College
Contents 1. Agaricus: A brief introduction 2. Systematic Position 3. Vegetative method of reproduction 4. Asexual method of reproduction. 5. Sexual method of reproduction. 6. Fairy rings 7. Economic importance 8. Food value.
Agaricus is a saprophytic fungus, commonly grows on damp wood, decomposing organic matters like humus, horse dung, etc.
SYSTEMATIC POSITION OF AGARICUS Kingdom Mycota Division Eumycota Subdivision Basidiomycotina Class Hymenomycetes Order Agaricales Family Agaricaceae Genus - Agaricus
VEGETATIVE METHOD OF REPRODUCTION IN AGARICUS: Dikaryotic Mycelium Fruit Bodies Spawn ( Mushroom seed) Small blocks Through artificial division
Asexual Reproduction method in Agaricus : Terminal or intercalary chlamydospores are developed on dikaryotic mycelium which on germination produce dikaryotic mycelium.
Sexual reproduction in Agaricus : 1 2 3 Plasmogamy Karyogamy Meiosis
Fig: A-B. Stages of Plasmogamy C-G Growth of mycelium by clamp connection
Fig: Development of Basidiocarp
Fig: A simple fruit body
Fig: Basidiocarp development by dikaryotic mycelia
Life cycle of Agaricus :
FAIRY RINGS
Economic importance Agaricus bisporus and A. campestris are common edible species. A. sylvaticus and A. placomyces are highly poisonous A. xanthodermus causes gastrointestinal disturbances.
Food Value Richest source of vegetable proteins Contain all essential amino acids in much higher amount than even egg Contains mineral nutrients such as Na, K, Ca, P and Fe. Contain folic acid Contains vitamins like B, C, D and K
References Sharma P.D. Microbiology and Plant Pathology, second edition; Rastogi Publication. Vashishta B.R. And Sinha A.K. Botany for degree students- fungi, revised edition; S.Chand publication
THANK YOU