Circulation of Nutrients Environmental Biology Unit 2 Advanced

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 – Provides elements for • metabolic processes • Constructing organic molecules • Decomposition – Provides mineral and nutrients for metabolism

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

Soil Types

Soil Horizons

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

Decomposers and Detritivores • Decomposers – 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.

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 • O 2 content • moisture

Comparison of soils • Tropical rainforest • Temperate forests

Nutrient cycling Nutrients in environment ph oto sy nth es decomposition producers decomposers g n di de e fe co mp os itio n consumers is

The carbon cycle Carbon dioxide In the air (CO 2) photosynthesis respiration Combustion (burning) Fossil fuels Coal, oil, gas, peat feeding Carbon compounds in plants Carbon compounds in animals decay

The Nitrogen Cycle

Energy and Ecosystems • 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 N 2 to NH 4+ 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 NO 3 - NO 2 - N 2 O N 2

Nitrogen Cycle Nitrogen in atmosphere (N 2) Nitrogen-fixing bacteria in root nodules of legumes assimilation animals Plants Nitrates (NO 3 -) Decomposers (aerobic and anaerobic bacteria and fungi) ammonification Nitrogen-fixing soil bacteria Ammonium (NH 4+) Denitrifying bacteria Nitrification Nitrifying bacteria Nitrites (NO 2 -)

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 plants animals runoff Weathering of phosphate from rocks Phosphate in soil Phosphate in solution leaching Chemical precipitation Detritus settling to bottom decomposers sedimentation

The Phosphorous cycle