Nutrient Circulation

1. Nutrient Circulation • Waste is in the form of • dead organisms: animals/ plants/ leaves • faeces • urine • All can contain nutrients and/or energy • If the nutrients are not made available again, the ecosystem will decline • Open ocean productivity is low • Any dead organisms are removed from the ecosystem • sink to ocean floor • Failure to recycle nutrients, reduces future growth within an ecosystem. • Farmers need to replace harvested nutrients with fertiliser

2. Nutrient Circulation • During degradation wastes are decomposed to release inorganic ions • This is called - Mineralisation • Can be absorbed by plants and used for growth • Circulation depends on activities of 2 groups • Detritivores • Decomposers

3. Detritivores • Detritivores = detritus eating invertebrates e.g Earthworms, woodlice • Turn large pieces of organic waste into small pieces (gain energy & nutrients for growth in doing so) • Make humus (important soil constituent –for aeration, water retention/ drainage) • Because they in turn enter food chains by being eaten by other animals (e.g birds), they recycle the nutrients (and energy) back into the ecosystem. • Also increase the surface area of the detritus, so that decomposers can act more quickly

4. Decomposers • These are bacteria and fungi • Saprophytic (obtain nutrients and energy directly from dead or decaying matter) • A range of microbes found within soil • Can secrete enzymes which degrade molecules e.g cellulase • External digestion, forming a soluble soup easily absorbed • Vital in e.g Nitrogen cycle, carbon cycle • Decomposers live freely in soil or can be found in detritivore digestive tracts

5. Rate of Decomposition • Type of detritus (coniferous litter is slower than deciduous) • Type and abundance of decomposers • Abiotic factors • temperature • moisture (humus) • aeration (humus) • nutrient availability (nitrogen)

6. Nutrient Cycling • Animals gain nutrients from food • birds, some animals go to salt licks • Plants/ microbes gain nutrients from soil • Macronutrients • required in large amounts • e.g N, P, S • Micronutrients • required in smaller amounts • e.g Se, Mo, Mn • All nutrients need to be soluble before they can be absorbed • Lack of water can lead to nutrients not being available

7. Biogeochemical Cycles • Minerals can be part of living world (biota) or non living environment (abiota) • e.g. nitrogen as protein or atmospheric gas • chemically transformed by e.g. lightning • or biologically fixed by e.g. Rhizobium • Soluble so often removed by leaching • Three cycles: • Carbon cycle • Nitrogen Cycle • Phosphorous cycle

9. Nitrogen Cycle fixation ammonification assimilation Ammonium denitrification nitrification nitrification nitrite

10. Nitrogen Cycle Ammonium nitrite converted into plant protein, nucleic acids etc. converted into animal protein, nucleic acids etc. Rhizobium sp. Fungi & bacteria uptake by plant roots of soluble nitrates Thiobacillus denitrificans, Pseudomonas, Clostridium Nitrosomonas Nitrococcus, Nitrobacter

11. Carbon cycle

12. Phosphorous Cycle

13. Phosphorous Cycle • Phosphorous essential to cell biochemistry • Phosphorous minerals are rel. insoluble • Continuously weathered from rocks • Solubility pH dependent • Plants obtain phosphorous from soil • Phosphorous absorption often aided by mycorrhizal associations (mutualism) • Animals obtain phosphorous from plants • Phosphorous availability often limits growth • Hence use of NPK fertilisers • Algal blooms induced by detergent effluent

15. Nitrogen Cycle • 5 major processes: • Fixation • converting atmospheric nitrogen into soluble nitrate • rhizobium bacteria (free or in nodules), lightning • Assimilation • uptake of nitrate into plant roots, incorporation into nitrogen containing molecules (protein/ nucleic acid) • In the cycle this is animal’s source of nitrogen • Ammonification • breakdown of dead/ waste materials to give ammonia • bacteria & fungi (saprotrophic) • Nitrification • conversion of ammonia into nitrates • 2 step process • ammonia to nitrite (nitrosomonas; nitroso species) • nitrite to nitrate (nitrococcus, nitrobacter; nitro species) • Denitrification • fixed nitrate lost by bacterial reduction to gaseous oxides of nitrogen (pseudomonas, clostridium) or nitrogen gas (thiobacillus dentirificans)