Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Ecology Practical report
06 March 2015

15:48

Materials and Methods

Three plants of each species (Iris pseudacorus, Kalachoë daigremontiana, and Vicia faba) wer
from the control group, which had been watered daily, and three plants of each species were
the group which had been exposed to drought conditions
...
These discs were then
give the "fresh weight" (Wf)
...


After 45 minutes had elapsed, the discs were gently blotted and reweighed
...

Relative water content was calculated with

Ecology
Practical
...
36, 39

Vegetation and Ecosystems Page 1

e selected
e selected from
l
...


minutes
...
eu
• Now the focus is on detecting life

Detecting terrestrial life from space
• Remote sensing
○ Satellites can monitor how vegetation reflects the sun's radiation
• Vegetation spectral signature
○ Leaves absorb most visible light, especially blue and red
○ 50% of near-IR is reflected
○ Different photosynthetic organisms gve different red-edge signatures
○ It's possible that extra-terrestrial life could give a red-edge signature
 ET plants could be purple
 Bacteriorhodopsin = purple alternative to chlorophyll

History of atmospheric oxygen
• 3
...
45bya
○ Very low oxygen
○ Earliest imprints of life
○ Earliest biosphere
 Anaerobes
○ Probably used volcanic hydrogen, hydrogen sulphid, or iron, to reduce CO2
• 2
...
85bya
○ Oxygen appears in atmosphere
○ Advent of oxygen evolving cyanobacteria
• 1
...
85bya
○ Oxygen stable
○ Age of cyanobacteria
○ 'vegetation'
 Algal mats
• 850-542mya
○ Oxygen increases
○ Soft-bodied ediacaran animals
 Venozoans
 Mat encrusters and mat scratches
□ Did not burrow
• 400mya
○ Terrestrial vegetation
○ Major impact on O2
• 359-299mya
○ Vast carboniferous forests
○ Giant arthropods
 Meganeuran dragonfly
Carbon fixation
○
• 251mya
○ Mesozoic
○ Permian/triassic mass extinction
○ Palaeozoic forests decline
GREAT DYING
Vegetation and Ecosystems Page 6

○ GREAT DYING
○ Low oxygen
○ Efficient archosaur respiration
 Air sacs
□ Pterosaurs
□ Theropods
 Flow-through lungs
□ Crocodiles
 Both
□ Birds
 More efficient than mammalian

Carbon Dioxide
• 30 billion tonnes of CO2 per year from fossil fuels
• Phytoplankton and vegetation remove around 75% anthropogenic CO2
○ 34% tropical forest
○ 33% grassland and shrublands
○ 15% temperate and boreal forests
○ 12% croplands
• Global warming
○ We're all fucking idiots
○ GHG
○ CO2 is very stable
○ Arctic ice at 2nd lowest level

Vegetation and Ecosystems Page 7

Climate Change
29 January 2015

12:48

• Carbon cycle disrupted by fossil fuel burning
• More carbon dioxide
○ GHG
• Mauna Loa observatory
○ Few local sources of CO2
○ Shown definite and large increase

•
•
•
•

FACE
Free Air CO2 Enrichment system
• Effects of increased CO2 on plants
• Plants incapable of clearing the amount of carbon dioxide being produced

Plants will grow in different places
Different animals
Changes to habitats
Different global distributions of habitats
• Different crops
• Changed growing seasons
• Questionable food security

• Flooding of coats
• Erosion of shoreline
• Increased estuary salinity

Vegetation and Ecosystems Page 8

•
•
•
•
•
•

Increased human mortality
Heat stress
Respiratory diseases
More communicable diseases
Increased mortality and injury
Malaria
○ 20-30oC optimal for Anopheles

A Simple Ecosystem - Tundra
03 February 2015

12:31

• Simple but globally important
• 1/3 of global soil carbon
Tundra is a type of plant community
• Occurs in extreme conditions
○ Very dry
○ Very cold
• Dwarf shrub and herb vegetation
○ No trees

• The whole area has kilometres deep permanent permafrost

Biodiversity
• Snow geese in summer
○ Migrate south in winter
• Even in summer the max
...
In top layers of soil, due to leaf litter
○ Enclosure experiment
 Fertiliser added to enclosed area, lemmings still there
 Outside left as control
 Control: 0
...
E
...
Pollutants
...
g
...
g
...
America
 Dutch Elm Disease
□ Introduced to UK through contaminated logs
• Temperature
○ Affect distribution of many species
○ Lovage Ligusticum scotium
 Grows on cold sea cliffs
 Global warming eradicating it from southern areas
○ Other plants require high temperatures
 Olive trees
 Small-leaved lime
 Navelwort
○ Some species able to acclimatise to changes in temperature
• Water
○ Deserts and lack of water
○ May be natural or a human phenomenon
○ Too much water can be an issue for other species
• Light
○ Some species only grow in shade/intense light
• Physical structure of soil
○ The distribution of pocket gophers in Colorado is affected by soil
○ They are only tolerant of deep soils of fine sands
• Chemical structure
○ Soils derived from acid vs basic rocks
 Different chemical characters
○ Soils are complex systems
 Biotic and abiotic properties

Explaining distribution
• Animals more complicated than plants as they move and may change their distribution more
easily
• Can be affected by changes in behaviour
• These changes can be brought about by environmental factors
• Chipping Sparrow (N
...
85bya
Invasion of proterozoic continent
• 1
...
2bya
○ Endosymbiosis
Phylogenetics
• Molecular studies
• 2 main lineages of green eukaryotes
○ Green seaweeds and unicellular algae
○ Freshwater green algae
Evolution of Land Plants from Freshwater Algae
• Freshwater to land ecological gradient not as great at the marine

Earliest Evidence for Terrestrial Plants
• Fossil spores from Ordovician
• Can see tetrad products of meiosis
• Dispersal in unfavourable environments

Charophyte Life Cycle
• Haploid gametophyte produces gametes
• Diploid zygote undergoes meiosis to give haploid gametophyte
Land Plant Cycle
• Includes sporophytes (diploid)

Earliest Plant Mega Fossils
• Cookesonia
• Mid-silurian/early devonian
○ 428-398mya
• Fossilised early devonian ecosystem
○ 410mya
○ Fungal mycorrhizae
○ Lichen
○ Ancient arthropods
○ detritivores

Vegetation and Ecosystems Page 35

Spore Producing Vegetation
04 March 2015

12:24

Most primitive living plants
• Bryophytes
○ Mosses
 15000 sp
...

○ Fossil record poor
○ Earliest 390mya
○ Lack lignified vascularisation
○ Mosses, liverworts
Water Relations in Mosses
• Endohydric mosses
○ Take water up through rhizoids
○ Internal water transport via non-lignified cells
• Ectohydric mosses
○ Water uptake and movement via plant surface

Moss Life Cycle

Vegetation and Ecosystems Page 36

Ancient Vascular Plants
• Lycophytes
○ 1,200 species
○ From Devonian
○ Living clubmosses
○ Dominated carboniferous forests
• Pterophyta
○ Devonian
○ Living ferns and horsetails
○ Modern horsetails
○ Bracken
 Most distributed fern
 Pioneer species
□ Spread by underground stem
 Fronds die in winter and grow in spring
○ Fern life cycle

Vegetation and Ecosystems Page 37



Vegetation and Ecosystems Page 38

Vegetation of the Dinosaur Era
09 March 2015

17:12

Carboniferous
• Giant horsetails
• Evolution of reproductive packages as environment became more challenging
○ Seeds
○ Amniotic egg
Seeds
• New ecological opportunities
• Stored nutrients enabled seedling roots to reach for water
• Inhospitable dry mountainous forest in late paleozoic
The Ovule
• Less vulnerable than free spores
Pollen
• Sperm
• Protected
• Pollen tube delivers sperm to ovum

Pteridosperms
• Seed ferns
• Ovules on leaves
• Arthropod pollination?
○ Co-evolution?

Paleozoic - Mesozoic Boundary
• End-Permian mass extinction
○ The great dying
• 96% marine, 70% terrestrial species killed
• 7 million year coal gap

• "disaster taxa" at start of Mesozoic
○ Lystrosaurus
 Beaked, at plants
○ Weedy Lycophytes began to grow
Late Triassic and Jurassic Vegetation
• Conifers
• Cycad
• Gingkgo
• Gymnosperms
• Living descendants
• Non-flowering seed plants
○ Wind dispersed
• Mega-herbivores
○ Sauropods
Boreal Forests
• Circumpolar conifers below Arctic Circle
Vegetation and Ecosystems Page 39

• Circumpolar conifers below Arctic Circle
• 1/3 world's forests
• 3 billion songbirds in Alaska/Canada alone

Cycad Pollen and Pollinators
• Plants male or female
• Weevil pollinated
○ Largest animal family
• Modern biodiversity
○ 305 species - subtropical
○ 38% on red lists, 12% near threatened status

Vegetation and Ecosystems Page 40

Flowers and Pollinators
11 March 2015

12:46

Cycad Pollinators
• Cycads do not have flowers
• Male or female
• Weevils are pollinators
○ Most abundant arthropods
Angiosperm Radiation
• Mid-cretaceous
• ~80mya
• >75% of plants
Evolution of Pollinator Insects
• Cretaceous radiations
• Co-evolution with flowers
Angiosperm Innovations
• Bisexual flowers
○ More efficient with animals
• Enclosure of ovules in carpels
○ Reduced self-pollination
Rewards for Pollinators
• Pollen - 40% each of sugars and protein
• Nectar - sugars specifically for pollinators
• Nectaries at base - pollinators brush anthers and stigma
Angiosperm Life Cycle
• Alternation of sporophyte and gametophyte generations
• Microscopic gametophytes in ovule and pollen
• Double fertilisation
○ One sperm and 2 haploid nuclei
 Triploid endosperm
○ 1 sperm fertilises egg --> diploid zygote
Animal Pollinators
• Insects
○ 2/3 of angiosperms
○ Bees most common
○ Floral attractors for bees
 Scented
 Tubular
 Landing platform
 Zygomorphic
 Not red
○ Beetles and lepidoptera prefer actinomorphic flowers
○ Butterflies
 Yellow, pink, purple
 Tubular
 Clustered
 Scented
• Birds
Nectarivorous birds worldwide
Vegetation and Ecosystems Page 41

○ Nectarivorous birds worldwide
○ Adapted tongues or bills
○ Ruby Throated Hummingbird
 19 Eastern USA plants
 Migrate to coincide with flowering
• Animals
○ Fruit bats - 173 species
○ Other mammals
 Honey possum
Wind Pollinated Flowers
• 10% angiosperms
• Grasses and forest trees
○ Too numerous?
• Lots of small, light, pollen
• Non-showy, often no petals
• Trees
○ Unisexual tree flowers reduce self-pollination
○ Trees flower early - fewer impeding leaves

Vegetation and Ecosystems Page 42

Angiosperm Biodiversity
12 March 2015

12:04

Taxonomic Ranks of the Daisy
Species Bellis perennis 1 member
Genus Bellis 15 members
• Initial capital for genus name
• Italics
Family Asteraceae 23,000 members
• Plant family names end in aceae
Order Asterales 27,500 members

19 major plant families
• Ranunculaceae*
• Chenopodiaceae
• Cryophyllaceae*
• Brassicaceae
• Rosaceae
• Fabaceae*
• Onagraceae
• Geraniaceae
• Apiaceae
• Boraginaceae
• Lamiaceae
• Scrophulariaeae
• Astericeae*
• Juncaceae
• Cyperaceae
• Poaceae*
• Liliaceae*
• Orchidaceae
*in practical
Ranunculaceae
• Relictual flora features
○ Many separate carpels and stamens
○ Ovaries can consist of fuse carpels

•

Caryophyllaceae
Vegetation and Ecosystems Page 43

Caryophyllaceae
• Some derived floral features
○ Fewer carpels and stames
○ Carpels fused in ovary

•

Fabaceae
• Derived floral features
○ Zygomorphic petals
 Bees?

•

Astraceae (last of dicots)
• Many derived features
○ Compound flowers of individual 'florets'

Vegetation and Ecosystems Page 44

○

Poaceae
• Many derived features
○ Composed of florets
○ Parts enclosed in 'bracts'

•

Liliaceae
• Many derived floral features
○ Monocot floral parts tend to be multiples of 3 (4/5 in eudicots)

•

Monocots
Embryos

Eudicots

1 cotyledon

2 cotyledons

Leaf venation Usually parallel

Usually netlike

Stems

Scattered vascular tissue

Usually arranged in ring

Roots

Usually fibrous

Usually around taproot

Pollen

Grain with 1 opening

Usually 3 openings

Flowers

Organs usually in multiples of 3 Organs usually in multiples of five

New Classification
Vegetation and Ecosystems Page 45

New Classification

Vegetation and Ecosystems Page 46

Ecological Adaptations of Photosynthesis
30 April 2015

12:21

• Most plants are C3
○ 3-carbon product of Rubisco CO2 fixation
• Rubisco has an alternative reaction
○ 2-carbon and 3-carbon products of O2 fixation
Stomata
• Stomata close on a hot, dry day
• Leaf [CO2] falls
• Photorespiration
• Rubisco reacts with O2, not CO2
• 2C compound metabolised
• 2C compound metabolised
• Can drain 50% of carbon from Calvin cycle
• 2 solution
○ Accumulate CO2 at night so stomata not needed on hot, dry days -> CAM photosynthesis
○ Circumvent problem of Rubisco reaction with C4 photosynthesis
CAM Pathway
• Uses PEP carboxylase - Higher CO2 affinity than Rubisco
• Night - stomata open
○ PEP carboxylase fixes CO2to 4-C organic acid
• Day - Stomata close
○ CO2 released to Calvin cycle
• Crassulacean Acid Metabolism discovered in succulent Crassulaceae
○ Convergent evolution - 40 families
○ Acid or saline habitats
C4 Pathway
• PEP carboxylase fixes CO2 in mesophyll to 4C compound
• 4C compound diffuses to bundle sheath via plasmodesmata
• CO2 released into Calvin Cycle
C3 and C4 plant distributions
• 15,000 C4 species - commonly grasses
• Warm, high light environments
○ Savannah and steppe grasslands
• C4 plants = 20-30% CO2 fixation

Rise of C4 grasslands
• 5-8 mya
• C4 vs C3 seen in herbivore tooth enamel
○ Enzymes discriminate C13
• High CO2 and low O2 during plant colonisation
○ No need for specificity of Rubisco
 Inefficient Rubisco was fine
○ Grasslands appeared mid-tertiary

Vegetation and Ecosystems Page 47

Seeds and Fruit
16 March 2015

11:55

Ecological and Evolutionary Importance
• Angiosperm seeds mostly animal dspersed
• Birds main frugivores
• Major factor in primate and fruit bat evolution
Small and large frugivores
• 4% of angipserms attract ants by feleshy structures attached to seeds
• Elephants disperse many toprical plants
Other dispersal mechanisms
• Falls or scatter
• Wind
• Water
From flower to seed and fruit

• Different pericarps
○ Dry
 Pod
 Grain
 Nut (hard, thick)
 Samara (wings)
 Capsules (lots in one
...
g
...
7 million hectares in Portugal and the Mediterranean
□ Iberian Lynx, Deer, and Eagle
□ Threatened by modern screw-caps replacing corks
Vegetation and Ecosystems Page 50

□ Threatened by modern screw-caps replacing corks
Monocot Stems
• Scattered vascular bundles
• Arborescent monocots
○ Not trees
○ Lack true secondary thickening
○ Fibres strengthen scattered vascular bundles

Vegetation and Ecosystems Page 51

Plants and Terrestrial Resources
16 April 2015

12:46

• Water moves up trees via xylem vessels
○ Cohesion and adhesion
○ Transpirational pull
Roots
• Absorbative interface with soil
• Root hairs increase SA
○ Single cells elongated
• Mycorrhizae
○ Symbiotic fungi
○ 80% of plant species
○ Enhance capture from soil
Mineral Deficiencies
• Plants need >16 minerals
• Leaf discolouration diagnoses deficiencies
• Human micronutrient (vitamin and mineral) malnutrition in >50% of global population
Adaptations to Drought
• Waterproof leaf surface
○ Thick cuticle
• Minimal leaf surface
○ Needles
• Succulent leaves/stems
• Rolled leaves

Vegetation and Ecosystems Page 52

Marine and Freshwater Vegetation
16 April 2015

12:48

• Plants originated in the sea
○ Some have returned
• 98% of water saline
• 1% brackish
• 1% fresh
Seagrasses
• Angiosperms
• Saline "meadows"
• Light - photosynthetic O2 passed along aerenchyma
• Dark - anaerobic respiration
• Diet for dugongs and sea turtles
• Habitat for seahorses, fish larvae and juveniles
• Rapid loss
○ Rivalling rainforests and reefs
Mangroves
• Salt tolerant trees
• Tropical-subtropical tidal mud zones
• 16 families - convergent evolution
• Red mangrove
○ Central America
○ Aerial roots with lenticels and aerenchyma for O2 exchange
• Black and grey mangroves
○ Upward roots with lenticels and aerenchyma
○ Low tide exposure
• Ecosystems
○ Invertebrates colonise submerged roots
○ Crab, fish, and prawn nurseries
• Salt tolerance
○ Salt exclusion
○ Salt excretion
○ Slat glands in leaf epidermis
Halophytes
• Strandline
○ Terrestrial plants at top of beach
 Tolerate salt spray and transient seawater
○ E
...
Sea rocket, sea sandwort, sea holly
• Saltmarsh
○ Intertidal land - brackish water
○ Salt-tolerant terrestrial vegetation
○ Pioneer species
○ E
...
Cordgrass, glassroot, sea aster
• Crops
○ Evaporating irrigation water can salinise soils
○ Affects up to half of irrigation schemes
○ Irrigated land provide 1/3 of world food
○ Halophyte mechanisms of agricultural interest
Freshwater Hydrophytes
• Free floating - Float on or under water
Vegetation and Ecosystems Page 53

• Free floating - Float on or under water
○ Duckweed
○ Water fern
○ Bladderwort
• Emergent - aerial foliage, submerged roots
○ Iris pseudacoccus
 Tolerates anoxia by dormancy of metabolism and growth
 Fleshy rhizome aids drought survival
○ Reedmace
• Attached floating leaf - Floating foliage, submerged roots
○ Water lily
○ Pondweed
• Gas exchange strategies
○ Aerenchyma conduct O2 to submerged plants
○ CO2 utilisation efficiency enhanced by carbon fixation pathways similar to CAM
photosynthesis in xerophytes
• Rice
○ Important food source
 2
...
5 to 1
...
from sources to sinks
 Loading at sources
 Water follows by osmosis from source cells and xylem
○ Unloading
 At sink
 Water follows by osmosis
 Phloem sap flows from high to low pressure
 Faster than diffusion
• Signal molecules
○ In phloem
○ Day length sensor in leaves - FT protein (Florigen)
 FT protein moves in phloem to buds, causing flowering
○ Future virus induced flowering biotech?
 Virus expressing FT

Vegetation and Ecosystems Page 56

Plant Mineral Nutrients and Uptake
22 April 2015

11:03

Oilseed Rape
• Produces 10
...
Managed Systems
• Natural
○ Very few remain
○ Closed system
○ Recycling of nutrients
○ Very limited net removal or additions
○ E
...
Great Plains
• Managed
○ Agriculture, forestry, amenities
○ Not closed system
○ Removal of nutrients in plant parts
Require additions of nutrients
Vegetation and Ecosystems Page 57

○ Require additions of nutrients
Soil
•
•
•
•
•

Inorganic component
Organic matter - 5%
Water - 25%
Solid mineral salts - 45%
Air - 25%

Supply of mineral nutrients
• Both inorganic and organic soil components contribute to the supply of minerals
• Inorganic
○ Nutrient elements derived from weathering of primary minerals
○ Mineral component also attracts and retains nutrient elements
• Organic
○ Nutrient elements released from breakdown of the organic components

Vegetation and Ecosystems Page 58

Soil Organic Matter
23 April 2015

12:10

• Inanimate organic component
• Biologically active component
• UK arable soils: 1-3% organic matter
• UK grassland: 8-20%
• Major source of minerals
○ Biologically active component breaks down the rest
• 10-15% identifiable
○ Polysaccharides
○ Polypeptides
○ Polyphenols
○ Simple organic compounds
○ Functional groups
 COOH
 Phenolic hydroxyl groups
 Amino grous
Inanimate Soil Organic Matter
• Majority of complex nature
• Structure largely undefined
• Contribute to soil CEC (capacity to attract and retain cations)
• Very stable
○ 1/2 life of more than 25 years
Biologically Active SOM
• Soil Bacteria
○ 1micrometre in diameter
○ Up to 1 billion/g
○ 2
...

 Chemoautotrophic
 Aerobic or anaerobic
○ Actinomycetes
 Filamentous strings of bacteria, resembling fungi
 Heterotrophic
 Range of substrates
 Typically anaerobic
 Give soil it's "earthy" smell
 Many produce antibiotics
□ Reduce competition
• Soil Fungi
○ Microscopic hyphae
 Up to a metre long
○ Yeasts grow as single cells
Some have specialised fruiting bodies
Vegetation and Ecosystems Page 59

•

•

•

•

•

○ Some have specialised fruiting bodies
○ Can break down resistant material
 Lignin, cellulose
○ Up to 50% of soil biomass
○ Groups
 Heterotrophs
□ Break down lignin and cellulose to simple compounds
 Mycorrhizae
□ Symbiotic with plants
 Pathogens
□ Infect and feed off plant roots
Soil Algae
○ Phyto-autotrophic - photosynthetic pigment
○ Some heterotrophs
○ Confined to soil surface
○ Important in colonising raw mineral surfaces in symbiosis with fungi - as lichens
Soil Protozoa
○ Large, single celled organisms - 5-50micrometres
○ Feed mainly on bacteria, sometime fungi and other protozoa
○ Largest consumes 10,000s of bacteria each day
○ Biomass only 1% of microorganisms
○ Amoebae, flagellates, ciliates
○ 1 million/g in arable soils
○ Exist in water films around soil particles
 Closely associated with organic matter and rhizosphere
○ Useful for rapid cycling of nutrients from their bacterial prey
○ Tissue higher C:N ratio (10:1) than their pre bacteria and fungi (5:1)
○ Release excess N2 as NH4
Soil nematodes
○ Non-segmented smooth worms
○ Typically 50micrometres in diameter, 1mm in length
○ Wide variety of types
 Bacterial and fungal feeders
 Predators
 Root feeders
○ Promote nutrient recycling
○ Can move further than fungi or bacteria - aid in distribution
○ Concentrated where prey live
○ 100/g in arable crop fields
○ 50-500/g in grassland
Earthworms
○ Decomposers - eat fungi and bacteria on organic matter
○ 1700kg/ha in pasture
○ Main effects
 Physical breakdown
 Mixing
○ Indirect effects
 Stimulated microbial activity
 Mix and aggregate soil
 Increase H2O infiltration
 Bury organic residues
 Indicate system health
 Create channels for roots
Soil Arthropods
○ Insects of upper soil layers
○ Large variation in size
 Mites to beetles
Vegetation and Ecosystems Page 60

○
○
○
○
○
○

 Mites to beetles
Few in arable soils - too much disturbance
Shredders - chew material
Predators
Herbivores
Fungal feeders
Consequences
 Increased surface area of residues
 Mixing of soil microbes
 Mineralisation
 Soil aggregation
 Porosity - burrowing

Vegetation and Ecosystems Page 61

Soil Physical Properties
27 April 2015

11:05

Weathering
• Physical
○ Freeze-thaw
○ Mechanical breakdown
 Water and ice
• Chemical
○ Carbonic acid
○ Nitric acid
○ Sulphuric acid
• Biological
○ Enzymes acting on minerals or metabolites in soil water
○ In presence of water, biological activity begins
 SOM
○ In arid regions, there's no water for biological or chemical processes
Particle Size Distribution
• <0
...
002-0
...
05-2mm = sand
• Sand and silt
○ Progressive breakdown of parent material
○ Generally quartz in temperate regions
○ "primary minerals"
• Clay
○ Reformed particles from products of weathering
○ Structures different to parent
○ "secondary minerals"
Soil Texture
• Reflects proportions of sand, silt, and clay
• Described by dominant size fraction
• Loam
○ Fairly even mixture of 3 components (40% sand, 40% silt, 20% clay)
○ Generally considered best physical and chemical properties for agriculture
• Clay
○ Strong influence on textural class
○ Only 40% clay makes it dominant
 80% sand or silt required
• Texture influences
○ Structure
○ Water characteristics
○ Workability
○ Strength
○ Drainage
○ Erosion
○ Fertility
○ Nutrient availability
○ Nutrient leaching
○ pH
Clay Minerals
• Structure
Vegetation and Ecosystems Page 62

• Structure
○ Aluminosilicate
 Si
 O
 Al
 Mg
 Fe
• Isomorphic substitution
○ Common in clay mineral formation
○ Metal ions replaced by one of lower valency
○ Overall negative charge
• Properties
○ Permanent negative charge and high surface area
○ Attracts and holds cations from soil solution
○ Quantified as Cation Exchange Capacity (CEC)
• Nutrients
○ Dynamic equilibrium
 Relative concentration between clay surface and in solution remains similar
○ In excess rainfall most ends up in solution
 Remainder held firmly on clay surfaces
○ Depletion by plat roots from solution
 Decrease in surface concentration to maintain equilibrium

Vegetation and Ecosystems Page 63

Soil Nutrient Cycling
29 April 2015

11:01

Soil Nitrogen Cycle
• Largest uptake by plants
• Increased dry mattter
• Soil contains 0
...
3% N
• Vast majority in organic form
• Virtually none in primary minerals
• Microbes responsible for cycling
• Nitrification
○ Nitrosomonas
○ Nitrobacter
○ Nitrobacter takes faster pathway
○ Nitroficication slower than ammonification at lower temperatures
• Denitrification
○ Warm, anaerobic conditions
○ NO3 -> NO2 -> NO -> N2O -> N2
○ 10kg/ha/year
○ N2O is a greenhouse gas
• Nitrate leaching
○ NO3- leaches
○ Risk to human health
○ Salad vegetables, water, processed meat
Soil Phosphorous
• Function
○ Nucleic acids
○ Energy storage
○ Phospholipids
• Cannot be replaced by another element
• 0
...
4% P in plants
• Taken up from soil mostly as dihydrogen phosphate
• In soils
○ Naturally occurring in crust, water, and organisms
○ Low concentration in minerals
○ Main source is sedimentary rock phosphates - phosphorite
 Diminishing resource - 72 years left
○ Most UK soils have P added
 Otherwise deficient
 Crops limited in Australia, S
...
Africa
• Fertilisers
○ 1842, Lawes patent for superphosphate manufacture
 From bones and mined rock phosphates
• Absorbed phosphate
○ Chemical precipitation
 Ca precipitates at high pH
 Al/Fe precipitates at low pH
○ Adsorption to soil surfaces
○ Added phosphate rapidly becomes unusable
• Movement in soil
○ Slow compared to nitrate
○ 5mm/week
○ Importance of mycorrhizal fungi
• Soil P vs
...
N
○ P within parent materials
○ P adsorbed or precipitated
 Low concentration in soil
○ Negligible leaching
○ No gaseous loss
Soil Potassium
• Taken up in large quantities
• Not in organic molecules
• Present as K+ throughout plant
• 1
...
2-50micrometres = micropores (storage)
○ <0
...
5-5
...
5-6
...
5-7
...
5-8
...
5
○ Nitrification inhibited below 5

---