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Circulation of Nutrients
Environmental Biology
Unit 2
Advanced Higher Biology
Learning Objectives
• Describe how organic matter is decomposed by the soil fauna
• Understand the importance of nutrient cycling
• Describe the nitrogen and phosphorous cycle
• Nutrient cycling
– Provides elements for
• metabolic processes
• Constructing organic molecules
• Decomposition
– Provides mineral and nutrients for metabolism
Soil Composition
• Dynamic medium
• Inorganic
– Weathering of rocks
– Sand, silt, clay
• Organic
– Death, decay
• Air and waterBedrock
TopsoilHumus
Leaf Litter
A
B
C
DIn
cre
asin
g O
rgan
ic C
on
ten
t Incre
asin
g m
inera
l con
ten
t
O
Soil Types
Soil Horizons
Soil Fauna
• Effect the quality of soil
– Fungi
– Bacteria
• In soil• Associated with the rhizosphere
– Invertebrates
• Earthworms, woodlice, nematodes, spiders etc
Decomposers and Detritivores
• Decomposers
– Bacteria and fungi
– Absorb organic nutrients from dead organisms and waste from living organisms, converting them into inorganic molecules
• Detritivores
– Organisms living in or on the soil that feed and gain nutrients from detritus.
Decomposition
• Breakdown of dead organic matter with release of inorganic nutrients into surrounding soil (mineralisation)
Litter Humusdecomposition
Rate of decomposition
• Factors
– Type of organic matter present
– Number and types of decomposers and detritivores
– Environmental conditions
• Temperature
• O2 content
• moisture
Comparison of soils
• Tropical rainforest • Temperate forests
Nutrient cycling
Nutrients in environment
decomposers
consumers
producers
photosynthesis
feed
ing
decomposition
decomposition
Fossil fuels
Coal, oil, gas, peat
Combustion (burning)
Carbon dioxide
In the air (CO2)photosynthesis
respiration
Carbon compounds in plants
Carbon compounds in animals
decay
feeding
The carbon cycle
The Nitrogen Cycle
Energy and Ecosystems
• Ecosystems
• Community
• Populations
• Habitat
• Ecological niche
• Food chains
• Food webs
• Producers • Consumers• Decomposers• Energy losses• Pyramids
• Number• Biomass• energy
The Nitrogen Cycle
• Most nutrient cycles have two components
– Geochemical– Biological
• Cycling of Nitrogen
– Nitrogen fixation– Assimilation– Ammonification– Nitrification– denitrification
Nitrogen Fixation
• Nitrogen gas converted to nitrogen-containing compounds.
• Three ways – all require energy
– Lightning
• nitrogen + oxygen oxides of nitrogen– Industrial processes
• Haber process – combine hydrogen and nitrogen to form ammonia
– Fixation by micro-organisms
Fixation by microorganisms
• Free-living nitrogen fixers
– Bacteria reduce nitrogen to ammonia– Used to manufacture amino acids– Nitrogen rich compounds released when die and decay.
• Mutualistic nitrogen fixers
– E.g. Rhizobium– Live in root nodules of leguminous plants– Nitrogenase converts N2 to NH4
+ using H+ and ATP– Requires anaerobic conditions (leghaemoglobin)– Plant uses ammonium ions to make amino acids
Assimilation
• Nitrogen assimilated in the form of ammonium ions
• Nitrate ions reduced to nitrite ions and then ammonium ions.
• Animals assimilate nitrogen in the form of protein
Ammonification
• Production of ammonium-containing compounds
– E.g urea, protein, nucleic acids and vitamins
• Decomposers feed on these releasing ammonia
Nitrification
• Two stages
– Oxidation of ammonium ions to nitrites
• Nitrosomonas
– Oxidation of nitrites to nitrates
• Nitrobacter
Denitrification
• Anaerobic denitrifying bacteria
• Reduce soil nitrates into nitrogen gas
NO3- NO2
- N2O N2
Nitrogen Cycle
Nitrogen in atmosphere (N2)
Plants
Decomposers (aerobic and
anaerobic bacteria and fungi)
Denitrifying bacteria
Nitrifying bacteria
Nitrites
(NO2-)
Nitrification
Nitrifying bacteria
Nitrates (NO3
-)
Ammonium(NH4
+)Nitrogen-fixing soil bacteria
ammonification
Nitrogen-fixing bacteria in root nodules of legumes
animalsassimilation
Nitrogen Cycle
The Phosphorous Cycle
Localised phosphate cycle
• Phosphate added to the soil by the weathering of rocks
• Producers absorb the soil phosphate
• Phosphorous transferred to consumers in organic form
• Animal excretion and decomposition returns phosphorous to the soil.
The Phosphorous cycle
Geological uplifting
Weathering of phosphate from rocksrunoff
Phosphate in solution
Chemical precipitation
Detritus settling to bottom
sedimentationdecomposers
animals
plants
rain
Phosphate in soil
leaching
The Phosphorous cycle