Ecology - Productivity Summary

Ecosystem Processes

  • Ecosystem processes include carbon sequestration, water purification, soil contaminant reduction, decomposition, productivity, and nutrient cycling.
  • Ecosystems provide cultural heritage, food, fiber, fuel, construction materials, pharmaceuticals, and genetic resources.
  • They regulate climate, provide habitats, regulate floods, and form the foundation for human infrastructure.

Productivity

  • Productivity is the rate of output per unit of input or the rate of new biomass production.
  • Photosynthesis and respiration drive the global carbon cycle.
    • Photosynthesis uses atmospheric CO2 (terrestrial) or dissolved carbonates (aquatic).
    • Respiration releases carbon back to the atmosphere and hydrosphere.
  • Primary Productivity:
    • Gross Primary Productivity (GPP): Total energy fixation by photosynthesis.
    • Autotrophic Respiration (Ra): Energy lost by respiration.
    • Net Primary Productivity (NPP): GPP−RaGPP - Ra, represents new biomass available for heterotrophic organisms.

NPP for Major Biomes (Pg C year-1)

  • Marine: Tropical and subtropical oceans (13.0), Temperate oceans (16.3), Polar oceans (6.4), Coastal (10.7), Salt marsh/estuaries/seaweed (1.2), Coral reefs (0.7), Total (48.3).
  • Terrestrial: Tropical rainforests (17.8), Broadleaf deciduous forests (1.5), Mixed broad/needle-leaf forests (3.1), Needle-leaf evergreen forests (3.1), Needle-leaf deciduous forests (1.4), Savannas (16.8), Perennial grasslands (2.4), Broadleaf shrubs with bare soil (1.0), Tundra (0.8), Desert (0.5), Cultivation (8.0), Total (56.4).

Patterns in Primary Productivity

  • Latitudinal, seasonal, and annual trends.
  • Variations related to internal or external sources.
  • Relationship of productivity to biomass.

Latitudinal Trends in Forest Type (g C m-2 year-1)

  • Tropical rainforest: 3249 (Mean)
  • Temperate deciduous: 1122 – 1507 (Range), 1327 (Mean)
  • Temperate coniferous: 992 – 1924 (Range), 1499 (Mean)
  • Cold temperate deciduous: 903 – 1165 (Range), 1034 (Mean)
  • Boreal coniferous: 723 - 1691 (Range), 1019 (Mean)

Source of Organic Matter

  • Autochthonous: produced by photosynthesis within an ecosystem.
  • Allochthonous: imported from elsewhere.

Productivity : Biomass Ratio (kgdry kgstanding-1)

  • Aquatic: 17
  • Non-forest: 0.29
  • Forest: 0.042

Net Ecosystem Productivity (NEP)

  • Net Ecosystem Productivity (NEP): carbon fixed in GPP that leaves the system as inorganic carbon via Ra or Heterotrophic Respiration (Rh).
  • Total Ecosystem Respiration (Re): Ra+RhRa + Rh
  • NEP=GPP–ReNEP = GPP – Re

Factors Limiting Productivity

  • Inefficient use of solar energy.
  • Water and temperature.
  • Drainage and soil texture.
  • Length of growing season.
  • Mineral resources.

Plant Defenses Against Grazers

  • Constitutive defenses: always present.
  • Induced defenses: produced when needed, potentially less costly.

Mineral Resources and Plant Defenses

  • Carbon Nutrient Balance Model (CNBM): chemical defenses vary with nutrient levels.
  • Nitrogen-poor soils: carbon-based defenses.
  • Increased nutrient levels: decreased carbon-based defenses, increased growth.

Chemical Defenses

  • Quantitative inhibitors: affect the amount of material herbivores process, require more time to mature for consumers, more energy for movement, and they are generalized feeding inhibitors (control decomposition rate).
  • Qualitative inhibitors: toxins that protect with dilute concentrations; herbivores evolve detoxifying mechanisms, leading to constant evolutionary movement.

Quantitative vs. Qualitative Defenses

  • Quantitative defenses: stable, produced once.
  • Qualitative defenses: less expensive, not chemically stable, need continuous replacement.

Factors Limiting Terrestrial Productivity

  • Amount of radiation, water shortage, mineral nutrient shortage, lethal temperatures, insufficient soil depth, incomplete canopy cover, low photosynthetic efficiency.

Factors Limiting Aquatic Productivity

  • Availability of light and nutrients (nitrogen, phosphorus; iron in oceans).
  • Limitations in streams, lakes, and oceans; productivity varies with depth.

Secondary production

  • NSP=GSP−RNSP=GSP-R
  • (Food eaten - Energy in faeces) - Respiration
  • Secondary Productivity: rate of production of biomass by heterotrophs.

Primary and secondary productivity

  • Productivity of herbivores less than plants. Not all plant biomass is consumed, assimilated, or converted to biomass.