Soil Processes and Accumulation Quiz

OM Accumulation

• Leaching: Removal of materials in solution from the soil by percolating water
• Calcification: Accumulation of carbonates, usually in desert areas, leaving a white powdery appearance
• Decalcification: The eluviation of carbonates
• Salinization: Accumulation of salts
• Desalinization: Leaching of soluble salts
• Alkalization: Accumulation of sodium
• Dealkalization: Removal of sodium
• Melanization: Darkening of light-colored minerals by the admixture of organic matter
• Leucinization: Paling of soil horizons due to the disappearance of dark organic materials
• Gleization: Reduction of iron under anaerobic, waterlogged conditions, with the production of bluish-greenish gray matrix color
• Pedoturbation: Biological and/or physical churning and cycling of soil materials
• Podzolization: Translocation of organic materials and sesquioxides from the upper soil horizon to the B horizon, creating a spodic horizon
• Desilication (Laterization): Removal of silica leading to the concentration of iron as ferric oxides under oxidizing conditions, forming laterite, an iron-rich subsoil layer in highly weathered humid tropical soils

Soil Orders

• Entisol: Young soils with little development
• Inceptisol: Slightly developed soils
• Alfisol: Moderately weathered soils with a good balance of nutrients
• Ultisol: Highly weathered soils with low fertility
• Oxisols: Extremely weathered soils found in tropical climates
• Spodosol: Soils with a spodic horizon, formed by podzolization
• Histosol: Soils with a high organic matter content (at least 20% mineral matter)
• Mollisols: Soils with a thick, dark topsoil, found in grasslands
• Vertisol: Swelling and shrinking clay soils, often found in rice fields
• Andisols: Soils formed from volcanic ash
• Aridisols: Desert soils with low fertility, typically dry
• Gelisols: Soils found in permafrost regions

Hans Jenny Equation: Soil = f(Cl O R P T)

• Forest vegetation and soil covary
• Global level: Influenced by climate
• Regional and local level: Influenced by parent material and topography
• Investigated with aerial photograph (stereoscope)

Boreal Forest

• High latitude, northern hemisphere
• Upper elevations of mountains
• Dominated by species from Genera Picea, Abies, and Pinus, with hardwood species of Populus, Betula and Alnus

Mineral Soil

• Decomposed by actinomycetes (break down cellulose and resistant materials)
• Leaching: Movement/removal of water-soluble sugars, polyphenols, and organic acids, resulting in increased palatability
• Fragmentation: Converting OM to smaller pieces by soil fauna, increasing surface area for bacteria and fungi colonization, speeding up decomposition

Forest Floor Decomposition

• Complex web of interactions among soil fauna and microorganisms
• Stages:
  • Pathogen invasion: Occurs while leaves/needles are still on the tree, disrupting cell integrity
  • Microbial conversion: Cellulose and carbohydrates are converted to CO2 and H2O, involving bacteria (heterotrophic, autotrophic, aerobic, anaerobic) and fungi (actinomycetes)
  • Condensation/humidification: Concentration of resistant organics, leading to high molecular weight carbon compounds, affecting soil physical, chemical, and biological properties, thereby forming humus

Factors Affecting Rate of Decomposition

• Substrate: High amounts of lignin and polyphenols = slow rate
• Temperature: Affects organism activity
• Moisture content: Affects organism activity through aeration and moisture supply

Tree Roots and their Significance

• Interface between soil and plants
• Influence soil properties
• Alter morphology and micromorphology
• Stabilize soil/slope: Prevent landslides and provide support
• Microtopography: Creates root disks, affecting soil morphology
• Concentration of OM: Annual production of fine roots exceeds leaf litter production
• Nutrient uptake and recycling: The nutrient pumping theory
• Formation of large continuous macropores: Increasing infiltration and soil by-pass contact
• Weathering: Accelerated decomposition through root exudates

Characterizing Root System

• Depth of rooting system: Typically shallow, uncommon to penetrate below 0.2 m depth
• Components of root system:
  • Structural roots: Large roots for stability and support
  • Fine roots: 1-2 mm in diameter, responsible for water and nutrient uptake
• Allometric Equation: Shows a general relationship between weight of individual tree components or between above and belowground biomass
• Interaction of tree roots and other plants: Competition for water, nutrients, light, and space

Mycorrhiza

• Symbiotic association between specific root-inhabiting fungi and fine feeder roots of plants
• Types: Ectomycorrhizae, Endomycorrhizae
• Naming: Based on the host plant

Benefits of Mycorrhizae to Plants

• Increase absorptive surface of roots
• Increase tolerance to stress (water, nutrients, disease)
• Increase access to unavailable ions (bound P)
• Deter infection by other fungi
• Increase access to organic N sources
• May negatively affect growth when soil is high in P

Benefits of Mycorrhizae to Fungi:

• Most must form mycorrhizal association to complete their life cycle
• Depend on photosynthate (carbohydrates and some vitamins) from plant host

Factors Affecting Mycorrhizal Development:

• Soil type, pH, chemical composition
• Climate, temperature, and moisture
• Plant species and their genetic diversity