Nutrient Cycles Flashcards
Nitrogen cycle 4 main stages
Ammonification
Nitrification
Nitrogen fixation
Denitrification
Ammonification
Production of ammonia from organic nitrogen- containing compounds (urea, proteins, nucleic acids, vitamins)
Saprobionts feed on faeces and dead organisms, releasing ammonia which then forms ammonium ions in the soil
Nitrification
Some bacteria obtain their energy from chemical reactions involving inorganic ions.
Oxidation of ammonium ions into nitrate ions so releases energy
Nitrifying bacteria
Aerobic conditions required (soil with many air spaces)
Nitrogen fixation
Nitrogen gas converted into nitrogen containing compounds (ammonium ions)
Carried out by
free living nitrogen fixing bacteria (reduce gaseous nitrogen to ammonia which they then use to manufacture amino acids)
Mutualistic nitrogen fixing bacteria (live in nodules on roots of legumes, obtain carbohydrates from plant and the plant acquires amino acids from plant)
Denitrification
Waterlogged soils, low oxygen concentration
Increase in anaerobic denitrifying bacteria
Convert soil nitrates into gaseous nitrogen
Reduces availability of nitrogen containing compounds for plants
Why do farmers plough fields
Keeps soul structure light and well aerated so plentiful oxygen for nitrifying bacteria
Good drainage
Prevents build up of denitrifying bacteria
Phosphorous cycle- source
phosphate ions in sedimentary rock deposits
Weathering and erosion of rocks- dissolves the ions (available for absorption by plants)
Mycorrhizae
Associations between certain types of fungi and the roots of plants.
Fungi act like extensions of the root system
Increases surface area for absorption of water and mineral ions
Acts like a sponge (holds the water and minerals so plant can better resist drought and take up inorganic ions more readily).
Mutualistic relationship
Fungus receives organic compounds (sugars, amino acids) from plant
Need for fertilisers
Mineral ions in the crops are removed from the ecosystem.
Becomes main limiting factor to plant growth
Productivity reduced
Two types of fertilisers
Natural (organic)- dead and decaying remains of plants and animals as well as animal wastes (manure and bone meal)
Artificial (inorganic)- mined from rocks and deposits and converted to different forms
How fertilisers increase productivity
Nitrogen needed for amino acids, ATP, nucleotides
Where nitrate ions are readily available, plants likely to develop earlier, grow taller and have greater leaf area- greater rate of photosynthesis. Q
Environmental issues with fertilisers (list)
Reduces species diversity
Leaching
Eutrophication
How fertilisers reduce species diversity
Nitrogen rich soils favour rapidly growing species (like grasses)
Out compete other species
Leaching
Rainwater dissolved any soluble nutrients and carry them deep into soil, beyond reach of plant roots and drain to streams
May have harmful effect of humans if lake source of drinking water- prevents efficient oxygen transport in babies, linked to stomach cancer.
Causes eutrophication
Eutrophication
Normally nitrate ion concentration is limiting factor for plant and algae growth in (freshwater) lakes as low concentrations
Due to leaching, concentrations increase so both populations grow
Upper layers or water become densely populated with algae (algal bloom) which absorbs light, preventing it from penetrating to lower depths
Light limiting factor for plants deeper so die
Saprobiont populations increase as decaying matter no longer limiting factor. Increased demand for oxygen so conc oxygen in water reduced and nitrates released from decaying organisms
Fish die
Anaerobic organisms increase in population size which release more nitrates and toxic wastes (H2S) makes water putrid
