PRODUCERS

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PRODUCERS

• READINGS
  FREEMAN, 2005
• Chapter 54 Pages
  1229-124

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Producers are autotrophs.

• Autrotrophs are organisms that can make their own
  food - complex organic molecules - from CO2.
• Such organisms include green plants and
  cyanobacteria (blue-green algae).
• These organisms use the energy of the sun to
  produce their own food from CO2 and H2O.
• Ecologists call these organisms producers.

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Producers and Photosynthesis

• The carbon (C) in organic molecules is found at
  very low concentrations in the atmosphere.
• The process by which producers use CO2 to make
  organic molecules is called photosynthesis.

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An Overview of Photosynthesis
SUNLIGHT
(H20)12

• Beginning in the 1770s experiments showed that
  the green parts of plants in the presence of
  sunlight, water, and carbon dioxide could release
  oxygen.
• By the 1840s it was known that carbohydrates
  (sugars) were produced and a rough formula for
  photosynthesis could be written.

(CO2) 6
C6H1206
(H20)6
(O2)6
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Conversion of Light Energy into Chemical Bond
Energy

• Photosynthesis concerts light energy into
  chemical bond energy by adding carbon, oxygen and
  hydrogen atoms to existing 5 carbon compounds
• This process increases plant mass, as measured by
  dry weight (biomass).
• Many other biomolecules and mineral elements are
  required for biomass production.

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Photosynthesis Takes Place in Chloroplasts

• At the plant level, photosynthesis takes place
  primarily in the leaf.
• Each leaf contains millions of chloroplasts.
• The chloroplast is the site of photosynthesis.

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Summary of Photosynthesis

• Green plants use light energy to convert carbon
  dioxide and water into sugar and oxygen.
• Sugars produced in photosynthesis are converted
  into biomolecules that make up the dry weight
  (biomass) of a plant.
• In short, plants are able to make themselves
  (organic molecules) from inorganic molecules
  (carbon dioxide and water).

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Atoms, Biomass and Nutrients

• C,H,O,N are the major atomic building blocks of
  living things. Their rank order of mass is
• 0 gt C gtgt H gt N gtgt 50 or so others
• A comparison of biomass with the make-up of the
  earth leads to the conclusion that life forms
  concentrate certain atoms.

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ATOMIC COMPOSITION OF VASCULAR PLANTS

• Recalling that biomass refers to dry weight,
  around 90 of plant biomass comes from carbon
  dioxide (CO2) in the air.
• H from water is the most abundant atom, but it is
  only 6 of plant dry weight (biomass).

ATOM of BIOMASS
O 45
C 45
H 6
N 1.5
50/- 2.5
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ESSENTIAL PLANT NUTRIENTS

• Macronutrients (those that make up 0.1 or more
  of biomass and, thus, required in relatively
  large quantities)
• O, C, H, N, K, Ca, Mg, P, S, (SI)
• Micronutrients (those that make up 0.01 or less
  of biomass and, thus, required in small
  quantities)
• CI, Fe, Mn, Zn, B, Cu, Mo, Ni, (Na),
  Co?, (Se)?

See Table 37.1 on page 854 In Freeman (2005) for
a more complete description of essential
nutrients
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Phosphorus Deficiency in Corn

• Phosphorous in the form of phosphate is a major
  ingredient in plant fertilizers.
• P deficient plants may remain greener than normal
  and develop a purple discoloration on leaves.
• Phosphate is an important constituent of DNA,
  RNA, ATP, and NADP.

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Nitrogen Deficiency in Corn

• Nitrogen deficiency results in young plants that
  are stunted in growth and pale green to yellow.
• N deficiency that occurs later results in a
  yellowing of the lower leaves.
• N is an important element in amino acids
  (proteins) and nucleic acids (DNA. RNA, ATP,
  NADP).

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Nitrogen (N) is the 4th major contributor to
biomass.

• The element nitrogen (N) makes up about 6 of
  plant dry weight.
• Nitrogen (N2) is approximately 80 by volume of
  the atmosphere. Yet, plants can not take in and
  utilize N2 by way of leaves.
• Only bacteria are able to fix and convert
  atmospheric nitrogen (N2) into forms that plants
  can use - ammonia (NH3) or nitrate (NO3) .

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SOIL

• Soil is the environment that provides the mineral
  nutrients for plant growth and development.
• It is a complex of inorganic particles, organic
  materials and living and dead organisms.
• During the process of soil development, the
  residues of plants, microbes and animals return
  more than the green plants take away.

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Soil Testing for Plant Nutrients

• Soil testing for macronutrients is a common
  practice among gardeners and agriculturists.
• Simple soil test kits give crude determination of
  N, P and K. The major ingredients of fertilizers.

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SOIL NITROGEN

• Stores of soil nitrogen can be quite high. Total
  N can reach 760 gN/m 2 in a tallgrass prairie.
  Rich forest soils can be as high as 550 gN/m 2 .
• Two sources of nitrogen are lightning and
  nitrogen-fixing bacteria.

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NITROGEN FIXATION AND LEGUMES

• Nitrogen fixation occurs when certain bacteria
  convert dinitrogen (N2) into ammonium (NH4) .
• Legumes are a large family of plants that form a
  mutualism with nitrogen fixing bacteria.

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Plant biomass increases as N increases and then
levels off.

• Plants of Old Field Goldenrod were grown in pots
  that contained total soil N that varied from150
  to 1650 mg N / kg of dry soil.
• Higher soil nitrogen yielded greater plant
  biomass up to about 1000 mg N / kg of soil and
  then biomass remained more or less constant.

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Intraspecific Competition for Nitrogen

• Since nitrogen is an important nutrient resource,
  one might expect that individuals compete for N.
• These experimental results confirm this
  prediction.
• Note that high density plants remain small at all
  N levels. Why?

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Interspecific Competition for Nitrogen

• The same experimenters examined two more species
  stiff golden rod (top) and little bluestem.
• Of the three, stiff golden reached maximum size
  at lowest N concentration little bluestem at
  highest.
• What would you predict concerning the outcome of
  interspecific competition between stiff golden
  rod and little bluestem?

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MAJOR FACTORS THAT INFLUENCE PRODUCTION

• As we have seen, nutrient availability can
  influence production as measured by biomass or
  seed set.
• Given the importance of water in photosynthesis,
  it is also a major factor in influencing
  production.
• Lastly temperature, particularly associated with
  day length and seasonality, influences production.

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PRECIPITATION AND PRODUCTION

• The effect of precipitation (water) is seen as
  one travels from east to west through the NA
  grassland biome.
• The tallgrass prairies of Illinois (top) receive
  about 36 inches per year.
• Those of western Kansas only about 15 inches.

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BIOMASS AS A MEASURE OF PRODUCTION

• Biomass is a universal measure of production.
• The change in weight of a cactus plant over a
  year can be used as a measure of production.
• Also, the change in weight of vegetation in a
  square meter of a desert from one year to the
  next can be used as a measure of production.

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NET PRODUCTION

• All plants not only increase in mass through
  photosynthesis, but like other living things they
  use some of that stored energy for respiration.
• That which goes unused is called net production.

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NET PRODUCTION, GROSS PRODUCTION RESPIRATION

• Plants accumulate matter (and energy) through
  photosynthesis (gross production).
• Plants use matter (and energy) during respiration
  (respiration).
• Net production Gross production -
• Respiration
• Production (Gross or Net) is either expressed in
  units of mass (g /m2 /year) or energy (kcal /m2
  /year).

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MEASURING NET PRODUCTION

• Field measurement of net production entails
  random plot assignment, clipping and sorting
  vegetation, drying and weighing plant material.
• Data is often reported as grams of biomass per
  square meter per year.

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Net production can be used to answer a variety of
experimental questions.

• Question Does fall burning decrease net
  production in a prairie community?
• Null Hypothesis No difference between burned and
  unburned plots.
• Method Burn a random sample of plots do not
  burn a random sample.
• Conclusion Reject null hypothesis. Results
  suggest that burning actually increases net
  production. Why?

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NET PRODUCTION IN SOME MAJOR BIOMES
Net Production / Unit Area (grams/meter 2
/year)
BIOME RANGE AVERAGE
Desert Semi-desert 0-250 40
Artic Alpine Tundra 10-400 140
Coniferous Forest 400-2,000 800
Deciduous Forest 600-2,500 1,250
Grassland 200-1,500 600
Tropical Forest 1,000-3,500 2,000
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PRODUCERS

• READINGS FREEMAN,
  2005 Pages 1229-1242