Soil

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Abiotic Environment 2
Soil
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• The Physical Environment Soils
•  
• Soil may be defined as a natural product formed
  from weathered rock by the action of climate and
  living organisms.
• Soil is a system consisting of mineral, gaseous,
  and aqueous components that occur on the land
  surface and occupy space.
• Soils are composed of both inorganic
  constituents and organic by products.

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• The Physical Environment Soils
•  
• Soil serves as a site for
• nutrient storage and delivery,
• nutrient transformation,
• water storage,
• waste deposition and processing,
• root anchorage for plants,
• burrowing and nesting, escape, etc.
• Soils and soil formation are related to
  variation in topography, climate and vegetation.

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• The soil profile consist of up to six layers or
  horizons
• O horizon- the surface layer, formed and forming
  above the mineral layer and composed of fresh or
  partially decomposed organic material that has
  not been mixed into mineral soil.
• A horizon-the upper layer of mineral soil with a
  high content of organic matter. It
  is characterized by the accumulation of organic
  matter and by the loss of some clay, inorganic
  minerals, and soluble matter.

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Leaching
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E horizon-the zone of maximum leaching
(eluviation). Its chemistry and
structure have been altered by the downward
movement of suspended and dissolved material
through weathering and leaching.
It is also characterized by the development of
granular, platelike, or crumblike structure. B
horizon-the zone of illuviation or collection of
leached material. It accumulates
silicates, clay, iron, aluminum, and humus
(organic material) from the E horizon.
It develops a characteristic blocky, columnar, or
prismatic structure.
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E Horizon
B Horizon
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• C horizon-this horizon contains weathered
  material, either like or unlike the material from
  which the soil is presumed to have developed.
  Some active weathering takes place, but it is
  little affected by soil formation.
• R horizon-unweathered bedrock below the C
  horizon.
• The O and A horizons support the greatest
  biological activity.

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Soil Profile a vertical cut through a soil
body or pedon
Pedon A 3D section of soil large enough to
study all the horizons and chemical properties of
a soil (1-100 m3)
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Properties of soils

• The important properties of soil are
• color,
• texture,
• moisture, and
• chemistry.
• These properties infer much about the
• - environmental conditions under which the soil
  is developing,
• water availability to plants,
• nutrient availability to plants, and
• soil quality as habitat for plants and animals.

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Properties of soils

• Texture is determined by the proportion by weight
  of particle size classes
• rock fragments (2.0 mm )
• sand (0.05 - 2.0 mm)
• silt (0.002 - 0.05 mm)
• clay (less than 0.002 mm)
• Also pore (gap) space in an idea soil 50
  if particle, 50 pore space
• Texture affects
• permeability and water storage capacity which
  affects oxygen status,
• which, in turn, affects soil color.

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Soil color
Bright colors aerated well drained
grey soils iron
white soils carbonates
Red yellow soils iron oxides
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Soil texture
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Soil structure

• Soil particles are held
• together in aggregates or peds.
• The arrangement of peds soil structure
• Soil aggregates can be granular, crumblike,
  platelike, angular blocky, prismatic, collumnar
  (see next slide)
• This structure is influenced by
• texture
• vegetation
• soil organisms
• soil chemistry

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Soil depth

• Soil depth varies from place to place depending
  on
• slope
• weathering
• parent material
• vegetation

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Soils under grasslands several meters
deep Under forests shallow A
horizon c. 15 cm B horizon c. 60 cm deep
Soils at the bottom of slopes deep Soil on
level ground deep Soils on alluvial
plains deep Soils on ridgetops shallow Soils
on steep slopes shallow Shallow soils have
lower fertility and water holding capacity.
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Soil moisture

• The amount of water per unit volume that a soil
  can hold is one of its most important
  characteristics.
• Field capacity is the maximum amount of water
  that a soil can retain after drainage by gravity.
  
• Wilting point is the water content at suction
  pressure 1.5 MPa (megapascals) or 15
  atmospheres - water at
  this point cannot be extracted by plants and they
  begin to wilt.
• The difference
• AVAILABLE WATER CAPACITY

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Soil moisture

• The available water capacity (amount of water
  retained by the soil between field capacity and
  wilting point) an estimate of the amount of
  water available for uptake by plants.
• Both field capacity and wilting point of a soil
  are influenced by
• soil texture
• organic content
• stoniness
• soil structure

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Soil texture affects soil water holding capacity
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Drainage

• Seven drainage classes
• Very excessively drained - plant roots just in
  upper layer of soil lack of water below
• Excessively drained - plant roots restricted to
  upper layer of soil because of water deficiency
• Well-drained - plant roots can grow to a depth
  of 90 cm without restriction due to excess water

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• Moderately well drained - plant roots can grow to
  a depth of 50 cm
• Somewhat poorly drained - plant roots are
  restricted by too much water beyond a depth of 36
  cm
• Poorly drained - wet most of the time typical
  vegetation alders, willows, and sedges
• Very poorly drained - water stands on or near
  the surface most of the year.

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Soil chemistry

• Clay is typically made up of silica (Si and O)

• Silica forms a tetrahedral shape - which can
  join via another oxygen to other silica
  tetrahedrons and form orderly sheets (Si2O5)n

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Soil chemistry

• Aluminum also bonds with oxygen to make an
  octahedron - which also forms sheets

• Silica sheets and aluminum oxide sheets form
  platelike micelles

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Soil chemistry

• An important feature of the micelles is that one
  element can substitute for another around the
  charged exterior of the micelle without changing
  structure (called isomorphous substitution).
• e.g. a Si4 can substitute for an Al3
• But as the incoming Al is only 3 vs the outgoing
  Si ions 4
• The miscelle unit gains a net 1- charge
• As a result, unit cells may have negative charges
  that must be balanced by positively charged ions
  (cations)

In turn Al3 could be exchanged for a Mg2 also
giving a net 1- charge
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Soil chemistry
These exchangeable cations are loosely held on
the surface of the micelles
and can be replaced easily by other cations.
The edges and sides of the micelles are
negatively charged and act as highly charged
negative ions (anions).
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Soil chemistry
As they are negatively charged, miscelles can
thus attract positive ions (cations), polar
water molecules and charged/polar
organic substances.
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• The total number of negatively charged exchange
  sites on these units that can attract positively
  charged cations
  cation exchange capacity (CEC).
• Negatively charge sites attract positively
  charged nutrient ions and helps prevent soil
  loosing these nutrient ions by leaching

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• The percentage of sites occupied by basic
  cations i.e.
• calcium
• magnesium
• sodium,
• potassium,
• percent base saturation.
• Acidic soils have a low percent base saturation
• -they have a high number of sites occupied by
  exchangeable hydrogen (H) ions instead of the
  above cations.

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Soils with a high CEC and high base saturation
are usually fertile (can retain lots of
nutrients) Unless they are saline (high Na
and Cl-) or contain toxic heavy metals.
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Soil formation

• Soil genesis - the breakdown of parent rock
  material into smaller particles - includes
  physical, chemical, and biological degradation of
  rock material,
• Whereas soil formation the development of soil
  with distinctive characteristics e.g. horizons.

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Soil formation

• The appearance of a soil at any point in time is
  dependent on many interactions between a variety
  of variables, such as
• climate
• parent rock material
• biological activity
• elapsed time
• (well developed soils can take 2,000 20,000
  years to form)
• (but soils can form in as little as 30 years)
• The deposition and decomposition of organic
  matter
• and the role of soil micro- and macro-organisms
• are especially important in the development of
  the O and A horizons.

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Factor in Soil formation Climate
Climate effects the nature and intensity of
weathering It also effects the type of
vegetation, which in turn can alter the soils
exposure to the effects of weather Climate
effects the amount of moisture entering
(precipitation) and leaving soils (evaporation)
and the nature of the precipitation (rain or
snow) Movement of water through the soil also
causes leaching which removed minerals in
solution effecting the soil
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Factor in Soil formation Parent material
Parent materials can be transported by a variety
of processes and deposited ontop of bedrock The
parent material regardless of how transported)
comes from rocks (igneus, metamorphic or
sedimentary) The chemical composition of these
rocks determine the chemical composition of soil
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Factor in Soil formation Topography
Topography effects the intensity of radiating
energy meeting the soil (e.g. N and S facing
slopes) Also the amount of water entering the
soil (i.e. runs off a steep slope) Steep slopes
are also effected by surface erosion and soil
creep (downslide of soil material)
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• Types of parent material
• Residual (In place)
• Igneous (Cooling of magna)
• Sedimentary rock (Deposition and compaction)
• Metamorphic (Changed igneous and sedimentary)
• Transported (Carried by wind, water, ice,
  gravity)
• Glacial ice
• Till (unsorted material carried in, ahead of, or
  under glaciers)
• Outwash (Water-deposited from glacial melt)
• Water deposition
• Alluvium (Eroded soil material carried and
  deposited by rivers and streams)
• Wind deposition
• Aeolian (Shifting sand)
• Loess (Nonstratified silt mixed with scattered
  particles of sand and clay)
• Gravity
• Colluvium (Erosional deposits on hillsides)
• Organic soils (Derived from plant material)

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Factor in Soil formation Biota
Vegetation provides organic material and effects
nutrient content of the soil Organic acids
produced by vegetation hastens weathering
(discussed later) Animals ingest plant material
and feces add organic material and
nutrients Earthworms and other burrowing
organisms effect soil structure Bacteria and
fungi break down organic mater Bacteria greatly
effect the nitrate content of the soil
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Factor in Soil formation Time
Rock weathering, erosion, mineralization etc. all
takes time Soils can form in 30 years but
2,000- 20,000 are often needed for a well
developed soil Soils develop more slowly in arid
conditions than humid ones If parent materials
are heavy in texture - soil develops more slowly
- less downwards water movement Flood plain
soils age little replenished regularly, and so
often are fertile (unleached)
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• Because of differences in parent materials,
  vegetation, topography, and climate, there is a
  great deal of both spatial and temporal variation
  among soils.
• On a local scale, if spatial variation relates to
  topography toposequence
• Differences in soils of different ages (but from
  the same parent material) chronosequences

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The Role of Biota
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• There is a reciprocal relationship between the
  soil flora and fauna and organic debris (litter)
  on and in the soil.
• The type and quality of the litter determine the
  composition of the biological community.
• that in turn influence the development of
  distinctive O horizon types called
• mull (dry acidic habitats matted
• moder
• mor.

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• mull forms in mixed deciduous forests, with
  moist soil and a good calcium supply.
• there is a thin layer of litter on the surface
  but lots of organic material in soil.
• organic material binds to soil particles
• low acid more bacteria (aids decomposition and
  increases nitrates)
• high biomass and biodiversity

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mor forms in dry acidic habitats matted or
compacted organic deposit resting on mineral soil
(a sharp break between O and A horizons) high
acid more fungi fungal content depresses
animal activity also less bacteria and less
nitrates
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moder midway between mull and mor plant
residues are turned into anthropod
(e.g. insect, annelid) droppings form small
organic fragments in heavy rain the droppings
act as a binding substance and a dense a dense
litter mat mor organic mater has less minerals
and less bound to soil particles than mull also
less nirates than mull
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ROLE OF BIOTA
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Types of humus (organic matter) formation in
temperate forests
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• Weathering
• Weathering involves the physical disintegration
  and the chemical decomposition of parent
  materials.
• Physical weathering - Physical disintegration
  breaks down parent material.
• Chemical weathering - Chemical decomposition -
  releases soluble materials and synthesizes new
  minerals.

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Soil development processes

• The interaction of vegetation and climate over
  broad regions results in four major soil
  development processes
• additions (of organic or inorganic
  material to any level of the soil)
• losses (of material from the soil
  leaching or erosion)
• translocation (of material up or sideways
  from one point to another)
• transformation (of mineral or organic
  substances, or the rearrangement of
  structural materials into peds)

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SOIL DEVELOPMENT PROCESSES Additions, Losses
and Translocations
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Soil developmentother processes
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Physiological Ecology 1
Adaptation
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• The Organism in its Environment Adaptation
• Adaptation is any heritable
• behavioral,
• morphological, or
• physiological trait
• that maintains or increases the fitness of an
  organism under a given set of environmental
  conditions.

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• The Organism in its Environment Adaptation
• Fitness of an individual is measured by the
  proportionate contribution it makes to future
  generations.
• It is not necessarily the number of offspring
  that an individual leaves behind that measures
  fitness
• BUT the number of descendants that influence the
  heritable characteristics (genetic makeup) of the
  population.

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• The differential reproductive success or fitness
  of individual organisms comes about through the
  process of natural selection.
• Under a given set of environmental conditions,
  those individuals most able to cope with the
  environmental situation are selected
  for, and those unable to do so are selected
  against.
• Thus natural selection selects for any heritable
  structural or behavioral characteristic that
  increases fitness.

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• Adaptations have typically arisen because of and
  result in long-term, elevated reproductive
  success for individuals carrying the particular
  trait.
• Therefore, the important criterion for
  reproductive success is the number of descendants
  that are left by an organism rather than the
  number of offspring produced.

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• Adaptation depends of genetic variation and
  genetic variation is essential for selection
  processes to occur.
• The lack of genetic variation restricts the
  ability of populations to respond to
  environmental change through natural selection.

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• Adaptation can also be considered in terms of
  the range of environmental conditions in which an
  organism can function,
• or its tolerance limits.
• Three important laws relate to the maximum and
  minimum environmental limits on organisms

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• Liebigs Law of the Minimum states that the
  growth of an organism is proportional to the
  single most limiting environmental requirement.
• Increases in other environmental factors will not
  result in increased growth until additional
  amounts of the limiting factor are added. This
  law applies only under equilibrium conditions.

???? If the growth of a plant is limited by a
nutrient (e.g. phosphate) its growth is limited
by the amount of phosphate available. But if the
quantity of phosphate increases, the level of
another nutrient might become limiting
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• Blackmans Law of Limiting Factors is an
  extension of Liebigs Law of the Minimum
  - there are both minimum and maximum levels of
  each environmental resource below which or above
  which the response of the organism would be
  limited.

???? A minimum amount of a resource can be bad,
but so can too much of a resource e.g. too much
heat can effect growth as much as too little heat
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• Shelfords Law of Tolerance - organisms are
  constrained by both the maximum and minimum
  extremes of an environmental condition thus
  these extremes represent the limits of tolerance.
  
• The response curve for an individual to
  increasing levels of an environmental resource is
  a bell-shaped curve.

???? The growth/response of an organism best
within a specific range of conditions. As these
conditions get further from the optimum (too high
or too low) so growth deminishes The goldilocks
laws
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• BUT the range of tolerance for an individual is
  not fixed.
• As seasons and conditions change, the
  individuals may acclimate to them and shift their
  tolerance curves to the right or to the left.
• However, all the shifting takes place within the
  adaptive physiological limits of the organism.
• This plastic, relatively short-term response of
  an individual to exposures of different or
  changing environments is acclimatization.

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Acclimatization
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• The variation among species in these basic
  characteristics arise
• - because no single set of characteristics
  enables an organism to function equally well
  under all environmental conditions.
• In other words - the characteristics that
  enables an organism to maximize its fitness under
  one set of environmental conditions
• limits its ability to do equally well under
  differing conditions.
• e.g. adaptations for a desert environment would
  be detrimental for a polar environment

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• Given the overall magnitude of external
  environmental variation, many organisms are
  capable of regulating their internal environments
  to some extent
• mostly by physiological means
• but also by morphological,
• and behavioral mechanisms.
• The maintenance of a relatively constant internal
  environment in a varying external environment is
  called homeostasis

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Homeostasis

• Homeostatic mechanisms control two basic
  responses
• negative feedback - halts or reverses the
  movement away from, and returning it back to, a
  set point (e.g. body temperature
  reducing a fever)
• - The response of the system and the response are
  inversely related (e.g. temp increases, the body
  acts to decrease temperature)
• positive feedback - is a response away from the
  set point where the response of the system is
  directly related to input (i.e. the situation
  escalates heatstroke, growth of cancerous
  cells)

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Plant adaptations
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• All life on Earth is composed of carbon-based
  compounds.
• To produce new tissues, for growth and
  reproduction needs additional carbon.
• Organisms gain this carbon by two methods
• Autotrophic (primary producers) are organisms
  that use inorganic sources of carbon i.e. carbon
  dioxide.
• e.g. plants, algae, and certain bacteria
• they energy derived from solar radiation to turn
  carbon dioxide into organic compounds.

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• Heterotrophs (secondary producers) gain organic
  sources of carbon by consuming other organisms or
  their by-products.
• Consumers are heterotrophs that feed on other
  organisms, living or dead.
• Decomposers are heterotrophs that feed
  exclusively on dead organic matter or waste
  products.

But first, autotrophs..
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• Plant Adaptations to the Environment
  Photosynthesis and the Light Environment
•  
• Photosynthesis is the process by which energy
  from the sun in the form of radiation in the
  visible spectrum (PAR) is harnessed to drive a
  series of chemical reactions.
• These turn carbon dioxide into carbohydrates
  (simple sugars) and the release of oxygen as a
  by-product.
• The synthesis of various other carbon-based
  compounds (proteins, fatty acids) from these
  initial products occurs in the leaves and other
  parts of the plant.

6 CO2 12 H2O C6H12O6 6
O2 6 H2O
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• Carbon dioxide is taken up into the leaf through
  openings in the leaf surface called stomata
• The diffusion or movement of carbon dioxide from
  the air outside the leaf into the leaf is driven
  by the concentration or diffusion gradient of
  carbon dioxide (high outside vs. low inside the
  leaf)
• Stomatal resistance - a function of both the
  density of stomata and the size of their opening
  - is the most
  important factor restricting flow of carbon
  dioxide into the leaf.

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• The opening of the stomata results in the loss
  of water vapor transpiration.
• This is a cost associated with the uptake of CO2
• The transpiration rate is related to the
  diffusion gradient of water vapor from inside to
  outside the leaf (i.e. less water vapor outside
  the leaf compared to inside increases
  transpiration)
• Since the air inside the leaf is saturated with
  water, the flow will be a function of the amount
  of water vapor (humidity) in the outside air.
• For the leaf to function it must replace this
  water lost through the stomata with water taken
  up through the root system from the soil and
  transported to the leaf.

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• To reduce the loss of water through
  transpiration, the stomata tend to close as the
  diffusion gradient increases
  (i.e. external humidity drops).
• This increased stomatal resistance reduces
  water loss
• -but it also reduces the uptake of carbon
  dioxide.

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• Photosynthesis is a complex sequence of
  metabolic reactions that can be separated into
  two processes
• The light reaction is the initial photochemical
  reaction - light energy is trapped in absorbing
  pigments called chlorophyll (within the
  chloroplast)
• This energy synthesizes adenosine triphosphate
  (ATP) from adenosine diphosphate (ADP)
• also NADPH from nicotinamide adenine dinucleotide
  phosphate (NADP).

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• The dark reaction transforms carbon dioxide into
  carbohydrates and does not require the presence
  of sunlight.
• It does depend, however, on the products of the
  light reactions.

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• There are three different, but related
  photosynthetic pathways
• C3 (Calvin cycle),
• C4
• Crassulacean acid metabolism (CAM).
• These pathways represent important physiological
  adaptations to moisture and temperature stress.

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• C4 plants carry on photosynthesis at higher leaf
  temperatures, higher light intensities, and lower
  carbon dioxide concentration than C3 plants
• - they generally are found in warmer and drier
  climates that C3 plants.
• CAM plants are succulent plants found in
  semiarid deserts they can open their stomata
  and turn carbon dioxide into malic acid at night.
  
• They close their stomata by day and use both
  fixed and respiratory photosynthesis in the
  Calvin cycle.

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• Alternative photosynthetic pathways
• C3 (Calvin cycle)
• C4

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• True or dark respiration involves the oxidation
  of carbohydrates (e.g., glucose) to generate
  energy in the form of ATP. Dark respiration
  takes place exclusively in the mitochondria.
• Dark respiration is often partitioned into two
  components
• (1) growth and synthesis and
• (2) maintenance.
• The first depends directly on the rate of
  photosynthesis
• and the second is proportional to the dry weight
  of the living tissue and is temperature
  sensitive.
• (CH2O)6 6 O2 6 CO2 6 H2O
  ATP

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• Total carbon uptake per unit time is a function
  of average rate of net photosynthesis
  (assimilation) per unit leaf area x total leaf
  area.
• Total carbon loss in respiration per unit time is
  a function of the total mass of living tissue.
• Net carbon gain photosynthesis respiration
• The net gain of carbon is allocated to a variety
  of processes.
• Some of the carbon will be used in maintenance
  respiration and the rest to synthesis of new
  tissues in the process of plant growth.

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• How the carbon is allocated will have a major
  influence on the survival, growth and
  reproduction of the plant
• to leaf tissue, to stem tissue, or to root
  tissue.
• Under ideal conditions, allocation to leaf
  tissue will promote the fastest growth by
  increasing photosynthetic surface, rate of carbon
  uptake and loss due to respiration.
• Allocation to nonphotosynthetic tissue increases
  the respiration rate without directly increasing
  the capacity for carbon uptake.
• But allocation of carbon to production of stem
  and root tissue is essential for the acquisition
  of key resources necessary (light, water,
  nutrients) for carbon uptake.

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• Plants respond to increasing light by increasing
  the rate of photosynthesis (rate of net carbon
  dioxide uptake). The response curve has two
  important points
• Light compensation point - the point of light
  quantity or flux where the rate of carbon dioxide
  uptake in photosynthesis exactly offsets the loss
  in respiration (net photosynthesis is zero).
• Light saturation point - the point at which the
  rate of photosynthesis reaches its maximum.
• The corresponding value of net carbon dioxide
  uptake at the light saturation point is called
  the light-saturated rate of net photosynthesis.
• Many C4 plants do not exhibit light saturation.

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• Response of net photosynthesis to variation PAR

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• Leaves grown in the shade typically can continue
  to maintain positive rates of carbon dioxide
  uptake under lower values of PAR.
• Plants grown in shaded conditions produce
  broader, thinner leaves and allocate more of the
  fixed carbon to leaf production and less to
  roots.

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• Species adapted to high-light environments are
  referred to as shade intolerant and are found
  growing in the upper canopy or in the open.
• Species adapted to grow in shaded habitats are
  called shade tolerant and can be found in the
  understory.
• These names refer directly to the observed
  difference in the light compensation points for
  these two types of plants
• - shade tolerant plants can continue net
  photosynthesis and growth at lower light levels
  than shade intolerant plants.

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Plant adaptations to variation in the PAR
environment
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Allocation of carbon in response to variation in
available light
More root production
More leaf production
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Response of seedlings of shade tolerant and
intolerant species growing in low- and high-
light environments
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• The daily periods of light and dark serve as a
  timing mechanism to keep plant activity in tune
  with the daily and seasonal changes in
  environment.
• The signal for these responses is critical
  daylength. When the duration of light or, more
  appropriately, dark, reaches a certain portion of
  the 24-hour day, it reduces or promotes a
  photoperiodic response of an organism to changing
  daylength.
• e.g. reaching critical daylength in spring can
  cause blossoms to bloom (blooming photoperiodic
  response)

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• Critical daylengths vary among species, but
  usually fall between 10 and 14 hours.
• Some organisms are day-neutral and are not
  affected by day length but by some other factor
  such as rainfall or temperature.
• Others are short-day or long-day. A colored
  pigment, phytochrome, is the key to the plants
  ability to detect changes in light and dark and
  measure the seasons.

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Periodicity and plant processes
Short-dayactivity is stimulated by daylengths
shorter than their critical daylength. Long-dayac
tivity is stimulated by daylengths longer than
their critical daylength.
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Timing of the opening of flowers of dogwood and
redbud across North Carolina
Seasonality in temperate and arctic regions is
mostly triggered by changes in light and
temperature.
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Timing of flowering and fruiting affected by
rainfall In tropical regions