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PRODUCERS
READINGS:
FREEMAN, 2005
Chapter 54
Pages 1229-124
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.
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.
An Overview of Photosynthesis
SUNLIGHT
• 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 1840’s it was known
that carbohydrates (sugars)
were produced and a rough
formula for photosynthesis
could be written.
(H20)12 (CO )
2 6
C6H1206
(H20)6
(O2)6
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.
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.
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).
Atoms, Biomass and Nutrients
• C,H,O,N are the major atomic building blocks
of living things. Their rank order of mass is:
0 > C >> H > N >> 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.
ATOMIC COMPOSITION OF
VASCULAR PLANTS
• Recalling that biomass ATOM % of BIOMASS
refers to dry weight,
around 90% of plant
O
~45%
biomass comes from
carbon dioxide (CO2) in
C
~45%
the air.
H
~6%
• H from water is the
most abundant atom,
N
~1.5%
but it is only 6% of
plant dry weight
50+/~2.5%
(biomass).
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
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.
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).
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) .
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.
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.
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.
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.
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.
QuickTime™ and a
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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?
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?
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.
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.
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.
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.
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).
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.
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?
NET PRODUCTION IN SOME
MAJOR BIOMES
BIOME
Net Production / Unit Area
(grams/meter 2 /year)
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
PRODUCERS
READINGS:
FREEMAN, 2005
Pages 1229-1242