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

• Inorganic

– Weathering of rocks

– Sand, silt, clay

• Organic

– Death, decay

• Air and waterBedrock

TopsoilHumus

Leaf Litter

A

B

C

DIn

cre

asin

g O

rgan

ic C

on

ten

t Incre

asin

g m

inera

l con

ten

t

O

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 Humusdecomposition

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

Nutrient cycling

Nutrients in environment

decomposers

consumers

producers

photosynthesis

feed

ing

decomposition

decomposition

Fossil fuels

Coal, oil, gas, peat

Combustion (burning)

Carbon dioxide

In the air (CO2)photosynthesis

respiration

Carbon compounds in plants

Carbon compounds in animals

decay

feeding

The carbon cycle

The Nitrogen Cycle

Energy and Ecosystems

• 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 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

Nitrogen Cycle

Nitrogen in atmosphere (N2)

Plants

Decomposers (aerobic and

anaerobic bacteria and fungi)

Denitrifying bacteria

Nitrifying bacteria

Nitrites

(NO2-)

Nitrification

Nitrifying bacteria

Nitrates (NO3

-)

Ammonium(NH4

+)Nitrogen-fixing soil bacteria

ammonification

Nitrogen-fixing bacteria in root nodules of legumes

animalsassimilation

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

Weathering of phosphate from rocksrunoff

Phosphate in solution

Chemical precipitation

Detritus settling to bottom

sedimentationdecomposers

animals

plants

rain

Phosphate in soil

leaching

The Phosphorous cycle