Lecture 10: Ricklefs 508-514

Nutrient cycling and productivity are sensitive to temperature, moisture, pH, etc., which influence plant nutrient uptake and microorganism detritus decomposition.
Organic detritus accumulates in soil, with unused biomass on top.
Four ways leaf litter breaks down:
1. leaching out soluble minerals and small organic compounds with water
2. detritivore (i.e. millipedes, earthworms, wood lice, other invertebrates) consumption
3. fungi breaking down larger carbohydrates including woody lignin (white rot does that)
4. bacterial decomposition

Mycorrhizae: fungi that work symbiotically with plant roots to extract nutrients and increase production. Mycorrhizae penetrate more soil than roots can do alone and secrete enzymes and acids to break down mineral nutrients in soil.
Two kinds of mycorrhizae:
Arbuscular: penetrate cell walls in roots and form branched structures close to cell membranes
Ectomycorrhizae: cover the exterior of small roots and penetrate root cortex spaces; most often on woody plants

Paths of Nutrient Regeneration

Depolymerization: breakdown of compounds in organic matter into monomers such as amino and nucleic acids
Immobilization: when microorganisms take up nutrients from the pool and incorporate them into their structures
Some microorganisms may then fix the nutrients (i.e. forming NH4), which are then either further converted or taken up by plants, and plants may also sequester the monomers that remain.

Climate can affect the pathways and rates of regeneration—for example, the tropical soils rapidly cycle the nutrients.

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