Tree of life Microbial Diversity Nutritional diversity Soil - - PowerPoint PPT Presentation

Tree of life

Microbial Diversity

Nutritional diversity

Soil bacteria

Schizomycetes

• Orders

– Pseudomonas – Eubacteria – Actinomycetes

• “Bacteria”
• 107-109 /g soil
• 106 /ml water

Myxobacteria

• Genus

– Myxococcus – Chondrococcus – Archangium – Polyangium – Cytophaga – Sporocytophaga

• “Swarm”
• consume insoluble
• rganics
• Intercellular

“communication”

Soil archaebacteria

Soil fungus

Eukaryotes + Prokaryote

Introduction

• What are soils?
• What are the general processes involved?
• How to microorganisms (and plants) contribute?

Rock weathering & decay

• Primary material must be broken down to

smaller pieces

– Increased surface area/volume ratio – Increased binding of nutrients – Release/binding of metals – Niche formation / chemical gradients

Soil texture

• Sand v. clay
• Porosity and retention

– Microorganisms – Air (aeration) – Moisture – Surface Area

• Influences?

Minerals

Microbial processes

Epilithic lichens

• Mechanism

– Physical (rhizine penetration) – Chemical (lichen-organic acids) – Crustose cover undergoes differential wetting and drying (and heat transfer)

• Results

– Grain detachment – Detachment by fractional heating

Microbial processes

Epilithic free living algae

• Mechanisms

– Photosynthesis / alkalinisation of rock surfaces – Extracellular polymeric substances (EPS)

• Results

– Dissolution of rock – Protective surface biofilm

Microbial processes

Chasmolithic and endolithic cyanobacteria, algae, chemo-

• rganotrophic bacteria and fungi
• Mechanisms

– Physical (swelling) – Chemical (acids, polysaccharides) through EPS – Differential heating due to pigments (melanins) – Turgor pressure

• Results

– Exfoliation, chipping, pitting – Increased porosity – Surface parallel cracking

Microbial processes

• Ideas of biological attack

– Photosynthesis (alkalinisation) by algae and lichens – Chemolithotrophic organisms (e.g…)

• Sulfate oxidising bacteria (sulfuric acid)
• Ammonia oxidising bacteria (nitric acid)

– Heterotrophic bacteria

• Consumption of organics
• Production of CO2 (CO2 + H2O = H2CO3)

Organics

Organics - terminology

Organic matter

Mineralisation

• Complete breakdown into

inorganic components

– Carbon dioxide – Nitrate / ammonia – Sulfate – Phosphate

• Fate

– Re-mobilised by biota – Redox changes – Gas transformation – Leach through pores – Sorb on to particles

Partial decomposition

• Formation of complex
• rganic radicals
• Polymerisation  humus
• Humus

– Small % of soil – (+) water capacity – (+) aggregation – (+) negative charge – (+) soil fertility

Organic matter

• Plant litter  most organic matter
• Some exceptions

– Lichens – Cyanobacteria – Fungi

• Some other bacteria that produce biomass from CO2

(inorganic C)

• Assimilated (biomass) / partly mineralised

Plant compounds

Storage materials (intracellular)

• Proteins
• Starch
• Sugars
• Chlorophyll
• Pigments

Plant compounds

Structural materials

• Cellulose
• Hemicelluloses

(polysaccharides that surround fibres)

• Lignins (stabilisers)
• Tannins (chemical defenses)

Plant materials

Storage materials (intracellular)

• Easily broken down and

assimilated.

Other compounds

Microbial compounds Black carbon

Humification

Humification

• Factors affecting decomposition

– Water potential – Oxygen supply – Temperature – Nutrients – pH

Humification

• Complex process

– Plant products  degradable products  monomers  microbial biomass – Plant products  un-degradable (incl. slow) products  re-assembled –  oxidized to humic precursors (humic and fulveric acids) –  complexation with clays and metal hydroxides

• Truthfully, very little is known of the process (esp. “rapid

re-synthesis of microbial biomass to polysaccharide and proteinaceous moeities in the humic fractions)”

Organic matter and humus

• Affects coexistence of plants, animals and microbes
• Regulate nutrient flux to microbes
• Hormonal role to plants
• (+) cation exchange capacity
• Buffer pH
• (+) water capacity
• Dark colour helps warm soil

Soil aggregation

AZ Master Gardener, ag.arizona.edu

Soil aggregation

• Benefits of aggregate abundance and stability

– Plant growth – Resistance to erosion – Soil organic matter turnover – Organism (incl. mesofauna and microfauna) abundance, activity and diversity

Microbial metabolites

• Polysaccharides

– Root exudates - carbohydrates – Bacterial EPS – polysaccharides, proteins, nucleic acids

• Glomalin

– Abruscular mycorrhyzal fungi – Recalcitrant – Insoluble to water

• Lipids

Biofilms

Microbial methods to improve soil aggregation

• Rhisophere microbial communities
• Organic residues
• Inoculation with microorganism
• Calcite-forming bacteria (bio-cementation)