Recycling within ecosystems

Decomposers - essential for nutrient recycling - convert complex organic compounds into simpler organic compounds.

  • Organism dies = break down tissues, releasing nutrients into soil

Nitrogen fixation

  • Nitrogen gas → nitrogen containing compounds

  • Azotobacter and Rhizobium bacteria contain nitrogenase enzyme to convert nitrogen and oxygen into ammonia

  • Azotobacter (free living bacteria)

    • Produce ammonia from nitrogen gas.

    • Make amino acids

    • Release them when they die

  • Rhizobium (mutualistic bacteria)

    • Live in root nodules in peas and beans - mutualistic (both benefit from each other) symbiotic (involving interaction between two different organisms living in close physical association) relationship

    • Obtain carbohydrates from plant and plant gets amino acids from bacteria

Ammonification

  • Production of ammonia from organic compounds e.g. urea, proteins, nucleic acids

  • Saprobiotic (organisms that digest their food externally and then absorb the products) microorganisms (bacteria and fungi) feed on these to release ammonia into the soil

Nitrification 1

  • Some microorganisms get energy from reactions involving inorganic ions (e.g. nitrosomonas bacteria)

  • Ammonium ions → nitrite ions (NO2-)

Nitrification 2

  • Nitrite ions → nitrate ions (NO3-)

  • This requires oxygen - occurs in soil with air pockets

    • e.g. aerated, well drained soil

  • Nitrobacter bacteria do this

Denitrification

  • Occurs when soils become waterlogged - short of O2

  • Anaerobic bacteria (Pseudomonas denitrificans) carry out denitrification

  • Soil nitrates → nitrogen in the atmosphere

  • Reduced nitrogen compounds available to plants - for land to be productive it must be kept well aerated