Soil Biota IISoil Biota II

Reading AssignmentReading Assignment

Soil Microbiology: Soil Microbiology: An exploratoryAn exploratoryApproachApproach

Chapter 4, 5,6 & 7Chapter 4, 5,6 & 7

The ChromistaThe Chromista

» Algae are oxygen evolving photosynthetic eukaryotes using H2O as an electron donor.

» Have a wide variety of shapes and both sexual and asexual reproductive forms.

» Morphologically algae may be either unicellular or filamentous.

Range in size from1 micron in microscopic species to over 30 m in marine species e.g. seaweeds.

The ChromistaThe Chromista

They are abundant in habitats in which moisture is adequate and light is accessible.

Most common and widespread plants.

The Chromista-Major GroupsThe Chromista-Major Groups

Major groups of Algae a.. Chlorophyta (greens)

b.. Bacillorophyta (diatoms)

c. Xanthophyta (yellow greens)

The Chromista-Major GroupsThe Chromista-Major Groups

a. Greens (Chlorophyta)

» Mainly unicellular

» Contain chlorophyll a and b

» Have a cellulose cell wall

» Store carbon reserves as starch

» Usually the predominant group in temperate climates.

The Chromista-Major GroupsThe Chromista-Major Groups

In soils they are usually unicellular Members of this group dominate algal flora

in acid soils. Good targets for predators like protozoa

earthworm and mice. Algae found on new rock surface i.e.

colonize first these surfaces leading to a climax community of some sort.

The Chromista-ClassificationThe Chromista-Classification

Examples: Chlorella Chlorococcus Dactylococcus Ulothrix

The Chromista-ClassificationThe Chromista-Classification

b. Diatoms (Bacillorophyta)»Unicellular »Contain Chlorophyll a and c»Cell wall made of overlapping

components made of silica.»Found in freshwater, marine and soil

The Chromista-ClassificationThe Chromista-Classification

Generally less frequent in acid soils, fare best in neutral and slightly alkaline environments.

Prominent members include Fragilaria and Navicula

The Chromista-ClassificationThe Chromista-Classification

b. Yellow (Xanthophyta) e.g. Botrydiopsis and Heterothrix» Relatively rare but their isolation is not

difficult.» Contain Chlorophyll a and c, and

carotenes, and xanthophyll» Have pectin in cell wall, a few have silica» Store carbon reserves as oil.» Reproduce by fusion of cells

The Chromista-EcologyThe Chromista-Ecology

1. Primary Colonizers in hot and cold desert ecosystems

2. Contribute to primary productivity, forms organic matter and improves

soil structure. 3. Forms association with other

organisms e.g. Lichens (with fungi) 4. Bottom of food chain.

The Chromista-EcologyThe Chromista-Ecology

5. More numerous than protozoa and macrofuana but less numerous than prokaryotes.

» Contribute to between 7 and 300 kg of biomass per hectare

6. Euthrophication in aquatic environments

7. Dinoflagellate produce toxin harmful to humans but harmless to shellfish.

The Chromista-ImportanceThe Chromista-Importance

1. Diatomaceous earth formed from siliceous cell walls of diatoms. Used in detergents, polishes, decolorizers, and deodorizers.

2. Alginates (salts of alginic acid) are produced principally by brown algae and are used as thickening , stabilizing or emulsifying in foods and beverages.

3. Kelps are used a fertilizers and food for livestock

The Chromista-ImportanceThe Chromista-Importance

4. Red algae are used regionally in Asia as human food and worldwide for the

production of agar.» Agar is widely used as additive in

pharmaceuticals, cosmetic and food.» In the laboratory agar is used for culturing

microorganisms (U.S. demand estimated about 106 kg per year).

3. Participate in decomposition of complex organic matter.

» The organic matter transformations brought about by filamentous fungi in well aerated environments often may be more prominent than the reactions catalyzed by bacteria.

4. They utilize proteinaceous substances and are therefore active in the

formation of ammonium and simple nitrogen.

» Under certain conditions fungi may compete with higher plants for nitrate and ammonium and lead to a decrease in soluble nitrogen content of soil.

5. They participate in the formation of humus from fresh organic matter. Species involved include Alternaria, Aspergillus.

6. Several soil borne fungi are pathogenic. Only very small portion of the fungi growing or surviving in soil is

concerned with plant disease.

Function and EcologyFunction and Ecology

» Species involved are generally classified in the genera Fusarium, Phytopthora, Pythium, Sclerotium etc.

7. They also form unique association with higher plants in the structure known as

mycorrhiza or fungus rot. 8. Fungi also form association with algae

known as lichens.