Nutrient Cycles

Nitogen Fixation:

• Atmospheric nitrogen gas converted into N-containing compounds
• Can be through N2 -> NH3 or NH4+    N2 -lightening--> NO3- (nitrate) and industrial use (Haber Process)

Ammonification:

• Breaks down organic nitrogen into ammonia or ammonium compounds. e.g. nucleic acids/amino acids
• Broken down by saprobiotic organisms (decomposers)

Nitrification:

• Carried out by nitrifying bacteria (needs aerated conditions)
• Oxidation reaction

Denitrification:

• Nitrates in soil are converted into nitrogen gas by denitrifying bacteria - occurs under anaerobic conditions (e.g. waterlogged soil)

• Phosphate ions are released from rock on land (by chemical weathering) and washed into soils
• They are absorbed by plant roots by active transport
• Used to produce ATP and nucleic acid to plant cells

Saprobionts:

• Known as true decomposers
• Secret a range of enzymes and can hydrolyse multiple different biological molecules

Organisms which secrete digestive enzymes onto the dead remains of other organisms:

• They then digest te biological molecules in these dead remains
• They then absorb some of the products of this digestion (ammonium, phosphate ions etc.)

Mycorrhizae:

• Receive sugars and amino acids (increases water uptake)
• Absorbs water and more minerals
• Fungi made up of long strands called hyphae that connect to plant roots (fungi obtain organic compounds, such as glucose, from the plant)
• All increases the total surface area for absorption of water and minerals

Eutrophication:

• 1 - Nitrates are leached from fertilised fields that stimulates the growth of algae in rivers and ponds
• 2 - Algae blocks light from reaching the plants below
• 3 - Plants die due to insufficient photosynthesis able to take place
• 4 - Bacteria feed on dead plant matter 
• 5 - Increased bacteria reduces the oxygen concentration in the water
• 6 - fish ie due to insufficient levels of dissolved oxygen

higher nitrae concentration results in an increased growth of algae due to an increase in DNA and cell division

Leaching - Water soluble compounds in soil washed away and often washed into nearby rivers and ponds. If nitrogen fertiliser is leached into water ways it can cause eutrophication

Natural:

Advantages - *Cheap *Improves soil structure *Can contain valuable macronutrients *Less soluble, inorganic ions released more slowely (prevents leaching)

Disadvantages - *Less concentrated (more is needed) *Smelly *Can contain unwanted substances such as weeds, seeds and fungal spores

Artificial:

Advantages - *Concentrated source of macronutrients can be appled in small amounts *Lacks strong smell *Easier to evenly spread

Disadvantages - *Lacks micro-nutrients *Expensive *Leads to eutrophication as nitrate and ammonium ions are very soluble so can leach out