Circulation of Nutrients Environmental Biology Unit 2 Advanced Higher Biology

Learning Objectives Describe how organic matter is decomposed by the soil fauna Understand the importance of nutrient cycling Describe the nitrogen and phosphorous cycle

Nutrient cycling Decomposition Provides elements for metabolic processes Constructing organic molecules Decomposition Provides mineral and nutrients for metabolism

Soil Composition A B C D Dynamic medium Inorganic Organic Weathering of rocks Sand, silt, clay Organic Death, decay Air and water Bedrock Topsoil Humus Leaf Litter A B C D O Increasing mineral content Increasing Organic Content

Soil Types

Soil Horizons

Soil Fauna Effect the quality of soil Fungi Bacteria Invertebrates In soil Associated with the rhizosphere Invertebrates Earthworms, woodlice, nematodes, spiders etc

Decomposers and Detritivores Bacteria and fungi Absorb organic nutrients from dead organisms and waste from living organisms, converting them into inorganic molecules Detritivores Organisms living in or on the soil that feed and gain nutrients from detritus.

Litter Humus Decomposition Breakdown of dead organic matter with release of inorganic nutrients into surrounding soil (mineralisation) Litter decomposition Humus

Rate of decomposition Factors Type of organic matter present Number and types of decomposers and detritivores Environmental conditions Temperature O2 content moisture

Comparison of soils Tropical rainforest Temperate forests

Nutrients in environment Nutrient cycling Nutrients in environment photosynthesis decomposition decomposers producers feeding decomposition consumers

The carbon cycle Carbon dioxide In the air (CO2) photosynthesis respiration Combustion (burning) feeding Carbon compounds in plants Carbon compounds in animals Fossil fuels Coal, oil, gas, peat decay

The Nitrogen Cycle

Energy and Ecosystems Producers Consumers Decomposers Energy losses Community Populations Habitat Ecological niche Food chains Food webs Producers Consumers Decomposers Energy losses Pyramids Number Biomass energy

The Nitrogen Cycle Most nutrient cycles have two components Geochemical Biological Cycling of Nitrogen Nitrogen fixation Assimilation Ammonification Nitrification denitrification

Nitrogen Fixation Nitrogen gas converted to nitrogen- containing compounds. Three ways – all require energy Lightning nitrogen + oxygen  oxides of nitrogen Industrial processes Haber process – combine hydrogen and nitrogen to form ammonia Fixation by micro-organisms

Fixation by microorganisms Free-living nitrogen fixers Bacteria reduce nitrogen to ammonia Used to manufacture amino acids Nitrogen rich compounds released when die and decay. Mutualistic nitrogen fixers E.g. Rhizobium Live in root nodules of leguminous plants Nitrogenase converts N2 to NH4+ using H+ and ATP Requires anaerobic conditions (leghaemoglobin) Plant uses ammonium ions to make amino acids

Assimilation Nitrogen assimilated in the form of ammonium ions Nitrate ions reduced to nitrite ions and then ammonium ions. Animals assimilate nitrogen in the form of protein

Ammonification Production of ammonium-containing compounds E.g urea, protein, nucleic acids and vitamins Decomposers feed on these releasing ammonia

Nitrification Two stages Oxidation of ammonium ions to nitrites Nitrosomonas Oxidation of nitrites to nitrates Nitrobacter

Denitrification Anaerobic denitrifying bacteria Reduce soil nitrates into nitrogen gas NO3-  NO2-  N2O  N2

(aerobic and anaerobic bacteria and fungi) Nitrogen Cycle Nitrogen in atmosphere (N2) assimilation Nitrogen-fixing bacteria in root nodules of legumes Plants Denitrifying bacteria animals Nitrates (NO3-) Decomposers (aerobic and anaerobic bacteria and fungi) Nitrifying bacteria ammonification Nitrification Nitrites (NO2-) Ammonium (NH4+) Nitrifying bacteria Nitrogen-fixing soil bacteria

Nitrogen Cycle

The Phosphorous Cycle

Localised phosphate cycle Phosphate added to the soil by the weathering of rocks Producers absorb the soil phosphate Phosphorous transferred to consumers in organic form Animal excretion and decomposition returns phosphorous to the soil.

The Phosphorous cycle Geological uplifting rain Weathering of phosphate from rocks plants runoff Phosphate in soil Phosphate in solution animals leaching Chemical precipitation Detritus settling to bottom decomposers sedimentation

The Phosphorous cycle