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Plant Ecology - Chapter 4

Plant Ecology - Chapter 4. Soils & Minerals . Soil Structure & Texture. Soil structure - physical arrangement of soil particles into aggregates Controls soil porosity. Soil Structure & Texture. Soil texture - proportional distribution of different-sized particles.

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Plant Ecology - Chapter 4

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  1. Plant Ecology - Chapter 4 Soils & Minerals

  2. Soil Structure & Texture • Soil structure - physical arrangement of soil particles into aggregates • Controls soil porosity

  3. Soil Structure & Texture • Soil texture - proportional distribution of different-sized particles

  4. Soil Structure & Texture

  5. Soil Structure & Texture • Loam soils have balance between sand, silt, clay • Equal parts of sand and silt, less clay • Generally most desirable for agriculture

  6. Soil Structure & Texture • Sandy soils - >50% sand particles - coarse texture • Hold water, minerals poorly • Warm quickly, cool quickly

  7. Soil Structure & Texture • Clayey soils - >35% clay • Hold large volume of water • Retain water and minerals well • Also retain pesticides, pollutants

  8. Soil Structure & Texture • Poor infiltration = greater runoff • Poor drainage, poor aeration • Slow to warm and cool

  9. Soil Structure & Texture • Silty soils - >50% silt • Intermediate in characteristics between sandy and clayey soils

  10. Soil Structure & Texture • Sand, silt particles irregular in shape • Clay particles plate-like or rod-shaped • Clay particles have large surface-to-volume ratio

  11. Soil Structure & Texture • Particle size, shape affects porosity • Pore space in sandy soils - 35-50% • Clayey soils - 50-60% - smaller particle size & arrangement (cluster together)

  12. Soil Structure & Texture • Clay particles usually bear strong negative electrochemical charge • Attract cations, such as important nutrients and water molecules

  13. Soil Structure & Texture • H, Ca, Mg, K, Na ions most abundant in soils in humid regions • Arid soils, H ions move to last on list, Na more important • All attract, hold water molecules

  14. Soil Structure & Texture • Cations attracted to clay particles partially available to plants • Exchange between particles, soil water • Ions can be taken up by plants from water, leached, or reattach to other particles

  15. Soil pH • Soil pH in U.S. - 3.5 to 10 • Native vegetation adapted to all pHs, but most ag crops grow best in slightly acidic soils • Changing pH has strong effects on nutrient and toxin availability, soil biota (bacteria, fungi)

  16. Soil pH • Forest trees especially tolerant of acidic soils • Conifers tend to increase acidity of soil (lower pH) via decomposition of needles

  17. Soil pH • Grasslands tend to grow on alkaline soils • Low rainfall results in soils with high pH

  18. Soil Horizons & Profiles • Soils contain layers - horizons • Sequence of horizons produces a soil profile • O, A, B, C, R

  19. Soil Horizons & Profiles • O horizon - organic matter

  20. Soil Horizons & Profiles • A horizon - topsoil • Region of maximum leaching - eluviation

  21. Soil Horizons & Profiles • B horizon - subsoil • Region of maximum deposition - illuviation

  22. Soil Horizons & Profiles • C horizon - undeveloped mineral material

  23. Soil Horizons & Profiles • R horizon - parent material (bedrock)

  24. Soil Development • Residual soils - develop in place by breakdown of bedrock • Ecological succession • 100s to 1000s of years

  25. Soil Development • Transported soils - carried from some other place - wind, water, glaciers

  26. Soil Development • 5 factors determine the kinds of soils that develop in an area • Climate, parent material, time, topography, living organisms

  27. Soil order

  28. Organic Matter, Organisms • Organic matter - humus - contributes, binds nutrients, retains water, acidifies soil (alters nutrient availability) • Organism actions alter porosity, structure

  29. Water in Soils

  30. Water in Soils

  31. Water in Soils

  32. Water in Soils

  33. Water in Soils • Hydraulic lift - deep-rooted plants pull water upward • Moves out into drier, shallow soils • Allows survival of shallow-rooted plants during drought, or in arid environments

  34. Plant Nutrients • Macronutrients and micronutrients • Essential vs. beneficial • Two most important for plants: nitrogen and phosphorus

  35. Nitrogen Fixers • Free-living nitrogen fixers - cyanobacteria • Flooded rice paddies, some surface soils

  36. Nitrogen Fixers • Symbiotic nitrogen fixers • Rhizobium, Bradyrhizobium on legumes - root nodules • Frankia on non-legumes • Cyanobacteria external to some plant roots - loose associations

  37. Phosphorus in Soils • Availability not directly related to amount present in soil • Phosphorus bound in ways that make it unavailable to plants • Bound to clay particles, metal ions, immobilized by microbes

  38. Evergreen vs. Deciduous • Evergreens often characteristic of nutrient-poor soils, soils subject to drought • Deciduous leaves require higher investments in photosynthetic enzymes, other proteins

  39. Mycorrhizae • Symbioses between various fungi, roots of terrestrial plants • Extremely common, widespread • Approach for dealing with phosphorus limitation, other nutrient shortages

  40. Mycorrhizae • Two major groups • Endomycorrhizae • Ectomycorrhizae • Endo- are most common, especially arbuscular mycorrhizae

  41. Mycorrhizae • Arbuscular mycorrhizae - most abundant where phosphorus is limited, in warm, dry climates • Important in tropical ecosystems, and for crop pants - woody and herbaceous • Fungal body grows inside root cells, with hyphae extending outward

  42. Mycorrhizae • Arbuscular mycorrhizae - associations not highly specific - same fungus may have many plant host species, or one host may have several fungal associates

  43. Mycorrhizae • Ectomycorrhizae - woody plants, especially temperate conifers • Hartig net between root cells, mantle network of hyphae outside root

  44. Mycorrhizae • Fungal hyphae increase nutrient uptake from soil • Transfer nutrients to root cells of host plants

  45. Mycorrhizae • Increased uptake, especially of phosphorus, results from higher surface area, and production of enzymes that release phosphorus from clay

  46. Mycorrhizae - more good • Improve metal uptake • Improve water uptake • Break down soil proteins • Protect roots from toxins • Protect plant from fungal, bacterial diseases

  47. Mutualism or Parasitism? • Fungi get carbon, energy from plant host • Plant gets nutrients, other benefits • Either “partner” can function as parasite at times - plant sheds fungus when times are good, or fungus gives little to plant

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