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IMPACT OF SOIL PROPERTIES ON SOIL MICROBIAL ACTIVITIES by Georgia Mori…
IMPACT OF SOIL PROPERTIES ON SOIL MICROBIAL ACTIVITIES
by Georgia Mori (138822)
pH: A measure of the acidity and alkalinity in soils
Soil acidification
Caused by:
Mineralization & oxidation of organic N and S release H+ ions
Decomposition of OM that causes release of CO2 into soil and formation of H2CO3
Increased H+ ions concentration with the released from C, N, S during transformation & cycling
Soil alkalization
Caused by:
Weathering of silicates, aluminosilicates & carbonate and subsequent release of OH- ions
Accumulation of soluble salts in the upper soil profile due to drought
Example of soil microbes and their optimum pH:
alkaline pH, not active < pH 5.5
Nitrosomonas
sp.,
Bacillus megaterium
neutral pH
Thiobacillus thioparus, Escherichia coli
acidic pH at pH 2-4
Thiobacillus thiooxidans, Thiobacillus acidophilus
Redox potential: The measurement of the tendency of an environment to oxidize or reduce substrates
Specific redox potentials of microbial processes:
0.15 to 0.2 V
Denitrification
-0.2 to 0.1 V
Methanogenesis
> 0.2 V
Aerobic carbon oxidation
-0.2 to 0.1 V
Sulfur reduction
Availability of Nutrient
Terminal electron acceptor
Molecular O2 is common electron acceptor in soil & reduce to H2O
Energy sources
Chemoorganotrophs & heterotrophs convert photosynthetically synthesized organic carbon to chemical energy
Chemolithotrophs capable of utilizing reduced minerals and cellular respiration products as energy sources
Macronutrients
Carbon, Nitrogen, Phosphorus, Sulphur
For cellular growth, building block for cellular biomass & cell proliferation
Growth factor
Required in small quantities, may also be used as C, N, energy source
When limited, leads to formation of resting structure (e.g. endospore)
Trace metals
Co required for synthesis of vitamin B12
Mo is required for nitrogen fixation & nitrate metabolism
Metallic ions essential for microbial growth
Moisture: The water held in the soil pore spaces
Soil moisture tension: A measure of how tightly the water clings to the soil particles
-8 to -30 bar
High soil microbe respiration
-50 bar
Soil microbe respiration is negligible
Water availability: The capacity of soil to hold water that is available for plant use
Optimal
Maximal levels of microbial activity
Low
Nearly non-existent levels of microbial activity
Fluctuation can happen due to:
Heavy rain
Daily impact on temperature/evaporation
Seasonal flooding
Temperature: The function of heat flux in the soil & heat exchanges between soil & the atmosphere
Different classes of microbes based on temperature tolerance:
15°C - 45°C
Mesophiles
< 20°C
Psychrophiles
> 45°C
Thermophiles
Soil microbes require temperature between 10°C - 35.6 °C for their activity, lower soil temperature will result in decrease in soil microbial activities
Limiting factor for microbial growth:
Time
Thaw rate
Free water
Aeration: The exchange of oxygen and carbon dioxide between the soil pore spaces and the atmosphere.
Oxygen depletion due to microbial respiration:
Decline in growth yield
Fermentation
Changes of predominant aerobic to anaerobic microbes
Methagenesis & sulfate reduction
Controlled by:
Gaseous diffusion rates
Respiratory activity of soil biota
Soil moisture
Concentrations of metabolizable OM