Nutrient Cycles

• There are 2 types of decomposers that will break down organic material

  1. Detritivores
  2. Saprobionts
• Detritivores


  Animals such as worms and woodlice that digest detritus (leaves, faeces).

  They break tissue down to increase the surface area for action by saprobionts.
• Saprobionts


  Organisms that secrete enzymes for extracellular digestion by creating small soluble molecules that diffuse into the saprophyte (another name for a saprobiont)
• Mycorrhizae


  Mycorrhizae are associations between certain types of fungi and the roots of plants. Fungi act like an extension of the plants root system and increase the SA for absorption of water and minerals.

  
  

  PLants benefit from improved water and inorganic ion uptake and fungi benefit from receiving organic compounds from the plant. e.g. sugars + amino acids (Mutualistic relationship)

  
• Soil fertilisers can either be:

  1. Organic - farmyard manure
  2. Inorganic - manufactured fertilisers that contain nitrates and phosphates
• Advantages to inorganic fertilisers

  • Nutrients are concentrated and can be applied in small amounts
  • Nutrients are released rapidly into soil
• Disadvantages to inorganic fertilisers

  • Readily leached from the soil
  • Can cause eutrophication in lakes and ponds
  • Expensive
• Advantages to organic fertilisers

  • Add structure to the soil
  • Provides useful means of disposing farm waste
• Disadvantages to organic fertilisers

  • Offensive smells
  • Difficult to spread
  • Nutrient release is slow
• Effects of nitrogen-containing fertilisers

  • Reduced species diversity
  • Leaching
  • Eutrophication
• Reduced species diversity

  Inorganic fertilisers favour the growth of grasses, nettles and other rapidly growing species which will out-compete other plant species. Meadows are species rich and have low nitrogen levels in the soil so will not survive if levels increase.
• Leaching


  Rainwater dissolves soluble nutrients and carries them deep into soils and out of reach of plant roots, eventually running into waterways. High nitrate ion levels in drinking water may be harmful to humans.
• Eutrophication


  Nutrients running into waterways increases the concentration levels on aquatic ecosystems. Main causes are fertilisers leaching off farm fields into surrounding water.
• Stages of Eutrophication

  1. Mineral ions from excess fertiliser leach from farmland into waterways

  2. Rapid growth of algae at the surface of the water (algal bloom)

  3. Blocks sunlight so aquatic plants below the surface die as they can no longer photosynthesise

  4. Algae start to die when competition for nutrients becomes too intense

  5. Decomposing bacteria feed on the dead organic matter and increase in number

  6. Bacteria use up the dissolved oxygen in the water through aerobic respiration

  7. Amount of dissolved oxygen in the water rapidly decreases, so aquatic organisms such as fish and insects may be unable to survive
• Nitrogen cycle

  
• Phosphorus cycle