Today

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• Today
• Finish energetics (Chapter 6)
• Start nutrient cycles (Chapter 7)

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Exam Wednesday!
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• Detritus (dead stuff)
• Assimilation efficiency of herbivores is only
  30-70
• most plant tissue is not digested by animals and
  ends up as detritus
• Two independent food chains
• herbivores
• most important in plankton communities
• detritivores
• terrestrial communities

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Gross primary production (GPP)
Respiration, maintenance
Decomposition
Net primary production (NPP)
Ingestion by herbivores
Indigestible
Respiration, maintenance
Assimilation
Growth
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Gross primary production (GPP)
Respiration, maintenance
Decomposition
Net primary production (NPP)
Ingestion by herbivores
Indigestible
Ecological Efficiency Biomass (higher
level)/ Biomass (lower level)
Respiration, maintenance
Assimilation
Growth
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Gross primary production (GPP)
Respiration, maintenance
Decomposition
Net primary production (NPP)
Ingestion by herbivores
Indigestible
Respiration, maintenance
Assimilation
Ingestion by predators
Growth
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• Residence time average time that energy spends
  on one trophic level
• (energy stored in biomass)/(net productivity)
• Biomass accumulation ratio residence time based
  on biomass rather than energy
• (biomass)/(rate of biomass production)

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• Nutrient Cycles (Chapter 7)
• General principles
• Water
• Carbon
• Nitrogen

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• With respect to energy, the biosphere is an open
  system
• energy from the sun is constantly being added
• energy is constantly lost to space
• For nutrients, the biosphere is a closed system
• no external source of nutrients
• all nutrients ultimately are recycled

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• A little chemistry
• Inorganic compounds do not include carbon (C)
  and hydrogen (H)
• CO2, NO2, H2S, PO4
• Organic compounds include C and H
• sugars, proteins, amino acids, nucleic acids (DNA
  RNA)

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• 3 types of chemical changes in n nutrient cycles
• Transformations between organic and inorganic
  forms of elements
• Assimilation incorporation of inorganic
  chemicals into organic molecules
• photosynthesis CO2 -gt sugar
• Dissimilation transformation of organic
  chemicals into inorganic forms
• respiration sugar -gt CO2

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• Transformations between different inorganic forms
  of elements
• N2 -gt NH3
• Changes in the energy state of chemicals

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• Each type of molecule has energy stored in its
  chemical bonds
• Breaking bonds frees energy
• Creating new bonds uses energy

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• Oxidized compounds (with oxygen) are usually low
  energy
• Reduced compounds (usually with hydrogen) have
  high energy

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• CH4 O2 ? CO2 energy
• reduced oxidized
• CO2 H2O energy ? C6H12O6
• oxidized
  reduced

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sugar ATP
protein
energy
energy
dissimilation
energy
dissimilation
assimilation
assimilation
assimilation
CO2 CO2 PO4 PO4
NH3
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• Nutrient cycles can be modeled as compartments
  connected by flows

soils (2 GT)
atmosphere (22 GT)
respiration (0.3 GT)
Flux
Pools
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• Water Cycle (units teratons, 1012 tons)

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• Solar energy causes evaporation
• Precipitation returns water to surface
• Water moves from oceans to land
• Water cycles rapidly between surface and
  atmosphere

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• Carbon Cycle
• Photosynthesis/respiration
• carbon assimilation in photosynthesis
  respiration by animals
• most photosynthesis/respiration occurs in oceans
• residence time 31 yrs
• Ocean-atmosphere interchange
• oceans absorb CO2 from air
• this buffers CO2 changes in the atmosphere

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• Precipitation of carbonates in water
• CO2 H2O ? H2CO3 (carbonic acid)
• Ca2 CO32- ? CaCO3

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• CaCO3 precipitates to form limestone, especially
  where plants take up CO2
• Ca is replaced by input from surface waters

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• Naturally, respiration balances assimilation, so
  CO2 levels stay roughly constant
• Burning of fossil fuels adds 6.5 GT, clearing
  forests 1.5 GT each yr
• CO2 levels increase by 3.2 GT each yr
• missing sink?

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Carbon Cycle (units gigatons, 109 tons)
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Nitrogen Cycle (units megatons, 106 tons)
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• Nitrogen (N)
• essential for proteins, DNA/RNA
• 70 of the atmosphere
• atmospheric form (N2) cant be used by plants
• often the limiting resource for plants,
  especially in oceans, deserts
• Nitrogen fixation conversion of N2 to NH3
  (ammonia) by bacteria or lightning

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• Nitrogen-fixing bacteria assimilate N2 and
  transform it into NH3
• some N fixation occurs in free-living soil
  bacteria
• most in roots of nitrogen-fixing plants
• Legumes plants in the pea family (Fabaceae)
• have root nodules inhabited by nitrogen-fixing
  Rhizobium bacteria

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• plants provide bacteria with carbohydrates
• bacteria reduce N2 to NH3, which can be used by
  plants

• Nitrogen fixation is most important in low-N
  environments, early in primary succession

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• Nitrification oxidation of nitrogen by bacteria
• NH3 ? NO2- ? NO3-
• energy-releasing reactions
• nitrates can be used by plants, but they have to
  be reduced (requires energy)
• In low-oxygen settings (oceans, soils,
  sediments), denitrification occurs
• NO3- ? NO2- ? NO ? N2O ? N2
• nitrogen is lost from the systems

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• Ammonification oxidation of carbon in amino
  acids, freeing ammonia

• carried out by all organisms when recycling
  proteins
• important in decomposition

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Phosphorus Cycle (units megatons, 106 tons)
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• Phosphorus
• used in nucleic acids, cell membranes, energy
  storage, bones/teeth
• often limiting in aquatic environments
• Most P occurs as phosphate (PO43-)
• absorbed from soil/water by plants
• bacteria oxidize organic phosphorus in detritus
• In aerobic water, precipitates and is lost as
  sediments

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Sulfur Cycle (units megatons, 106 tons)
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• Sulfur - used in amino acids
• Most organisms acquire S as sulfates (SO42-) and
  assimilate S by reduction
• Bacteria and atmospheric O2 oxidize organic S in
  detritus, creating SO42-
• In anaerobic environments, bacteria use sulfates
  as an energy source and produce S or H2S