Circulation of Nutrients

Provides:

decomposition releases minerals and nutrients for metabolic processes

essential elements for processes like photosynthesis, building amino acid and nucleic acids etc

Decomposition

•Dead or waste organic matter converted to inorganic nutrients

•Un-decomposed material is litter

•fully decomposed material is humus

•physical and biological process

•detritovores - detritus eating invertebrates

•microbial decomposers - bacteria/fungi

•fixed, lost and transformed nutrients

environmental conditions e.g. temp, moisture, aeration, nutrient availability

Mineralisation – release of minerals essential for life

type / abundance of decomposers

type of detritus

Decomposition rates influenced by:

Detritus converted to humus (small pieces ofmaterial more easily broken down by microbes

Nutrient Cycling

nutrients required by living organisms

trace elements, zinc, magnesium, iron, etc.micro

nitrogen, carbon, phosphorus, (sulphur)macro

nutrients can be macro or micro

from ingested materialanimals

from soilplants

Nutrient Cycling

nutrients in biogeochemical cycles

chemically transformed by biological or environmental processes

taken up or lost by absorption or leaching

fixed in biotic and abiotic components

Nitrogen cycle (80% stable)

converted by redox reactions to useful compounds

5 main steps

1. Biological nitrogen fixation

• gaseous nitrogen converted to ammonia

• Rhizobium bacteria (free living or symbiotic in nodules in legumes)

• prokaryotic bacteria or cyanobacteria

1. Biological nitrogen fixation

• anaerobic conditions, needs energy

• enzyme nitrogenase.

• leghaemoglobin in nodule bacteria fixes oxygen giving anaerobic conditions

2. Nitrificationammonia converted to nitrates by soil involves

many bacterial groups

Nitrosomonas/Nitrococcus convert ammonia to nitrites

Nitrobacter oxidises nitrites to nitrates (energy release)

3. Assimilation

Initial uptake of ammonia/nitrates by primary producersto make protein/nucleic acids.Consumers eating at various trophic levels

4. Ammonification

Decomposition to produce ammonia by bacteriain soil and aquatic ecosystems

5. Denitrification

Nitrates converted to nitrogen gas by free livinganaerobic denitrifyng bacteria(agrobacterium and psuedomonas)

Loss of soluble nutrients

Loss of soluble nitrates by leaching and run-off

Water saturation creating anaerobic conditionsreduces nitrification

Limits to nitrogen in environment

Tropical rainforest decomposition is rapid but soilquality is poor due to scarcity of humus and litter,leaching removes nutrients quickly

Temperate forest decomposition slower, soil qualityis good as litter and humus in plentiful supply

Crop rotation and addition of fertilizers

Carbon cycle

Phosphorus cycle

Phosphorus

animals excrete, organisms die and decomposition returns phosphorus to soil

animals consume phosphorus and assimilate it

plants take up phosphates and assimilate it

occurs as phosphates in soils from weathered rocks

local cycling of phosphate bound by humus and soil particles

nucleic acids, phospholipids, ATP, minerals in bones and teeth

Eutrophication

Results from too much phosphorus or nitrogen in aquatic ecosystems

plants and algae grow rapidly and die

decomposition of plant material uses lots of oxygen from water

other organisms e.g. fish unable to survive low oxygen levels