Primary Productivity in a Grassland
A. BIOLOGICAL MASS
– mass of organisms per unit
area of ground time
-also known as biomass
• 1. PRIMARY PRODUCTIVITY – the rate at which
primary producers assimilate solar energy in a
a. PRIMARY PRODUCERS – plants and the other
chlorophyll-bearing organisms that form the point of
entry for energy flow in the ecosystem
b. PHOTOSYNTHESIS – process of converting light
energy to chemical energy and storing it in the form of
c. NET PRIMARY PRODUCTIVITY- the amount of
energy left after removing the respiratory heat
• 2. SECONDARY PRODUCTIVITY – the rate of
biomass production by heterotrophs
C. FACTORS AFFECTING
• 1. TEMPERATURE – regulates the rate of physiological
processes and influencing growth and developments of
• 2. WATER – Water is required by all living organisms . Plant
can be stressed by lack of moisture as well as an excess
• 3. LIGHT – Sun plants are dependent on light for survival.
On the other hand, decrease in light can become a limiting
factor to plant growth for it slows the rate of photo synthesis.
• 4 NUTRIENTS – Nutrient deficiencies in the soil resulted in
reduced forage production, modified vegetation composition
and altered nutrient content of the forage.
• 5. ATMOSPHERE – The atmosphere contains gases
required for photosynthesis (CO2) and respiration (O2) is
the source of nitrogen.
• -process whereby an ecosystem
changes from simple community into
a complex and relatively stable one.
• SECONDARY SUCCESSION-
regeneration of the living community
after a major disturbance.
A. Measure the net primary productivity
in different micro habitats of a
B. Understanding the factors affecting
or limiting primary productivity in
• Bamboo sticks
• Meter Sticks
• Old newspapers
• Plastic string
• Triple Beam Balance
A. Select two vegetated micro sites in
grasslands with different light conditions
(open and shaded)
• Question: Why were the sites compared
different in light conditions?
• This is due to the fact that light affects
photosynthesis which influence the rate of
productivity of a producer. In the two micro
sites (open and shaded), the open region
has an abundance in light while the
shaded region does not.
B. Lay out the three (3) randomly spaced 0.5 x 0.5
m quadrants in each micro site. Use for bamboo
sticks to mark the four corners of each quadrant.
Enclose each quadrant with a string to mark the
• Question: why do we use 0.5 x 0.5 m quadrants?
• This is because a quadrant too large is not easy to
measure. The said quadrant size is enough for observation
on the rate of productivity.
• Question 2: Why do we place the quadrant randomly?
• This is so that the dominant species on each area will
have diversity in speciation.
C. Describe the species composition present in
each of the quadrants in the two (2) micro sites.
List the monocot and the dicot species observed.
• Question 1: Why do we need to list the species?
• The reason for such is that it helps us identify the
pioneer species that occupies the niche and
compare the dominant species inhabiting each
• Question 2: Why do we need to differentiate and
determine the dicot and monocot plants?
• This is done so that we could observe the effect
of sunlight on both plant classes (angiosperms)
and its effects on the recorded weight of
• The difference in weight from gathered data can
be explained by the difference in morphology and
energy requirement in plant development.
D. Cut the biomass above the ground in all
quadrants using a pair of scissors, and
discard the harvested biomass.
• Question: Why is there a need to cut the
plants in the said quadrants?
• This is because there is a necessity to
remove the inhabitant (pioneer) species
in order to start with zero productivity and
to open the niche to other plant life.
• Question: Why should only the plants
above ground be cut?
• This so that we could measure the
productivity of the pioneer species.
• Cutting the roots would only
eliminate pioneer species from the
quadrant which leaves no productivity
to measure except for the new
species that occupy the niche.
E. After 28 days, harvest the regrowth from each of
the quadrants. Separate the monocots from the
dicots. Oven-dry them separately. Label each
• Question 1: Why only after 28 days?
• The specified number of days are sufficient to
observe the changes in each micro site.
• Question 2: Why is there a need to dry-oven?
• This is so that the water within the plants will
• Why was the vegetation cut at the start of the
The vegetation was cut at the start because it is
easier to measure productivity rate from zero.
• Were the species present before the start of the
experiment the same species that were harvested
after 3 weeks? Explain.
No, only some were left present yet since the site
became open, new species grew in the area.
• Why should NPP be calculated based on dry
weights of biomass?
NPP should be calculated on dry weights because
water is not included in recording a plant’s
• Explain the difference in NPP between the two
NPP in the open region is higher than in those in
• Do you think the NPP in these
microhabitats remain the same for the
No, it will not remain the same due to
changing weather conditions and some
other environmental factors that affect
productivity of plants, particularly the NPP.
• What is secondary productivity? How does it
relate to primary productivity? And to Energy
pyramids in ecosystems?
Secondary productivity is the rate of biomass
production by heterotrophs.
Secondary productivity depends upon the growth
of primary productivity. (high primary productivity = high
Secondary productivity affects the energy pyramid
in the ecosystem through the transformation and
conversion of energy that may affect the
productivity of species. When there is an increase
in trophic level, the energy decreases.
• Among the different biomes of the world, which has/have
the highest NPP? Which has/have the lowest? Explain.
Tropical forests have the highest biodiversity and primary
productivity of any of terrestrial biomes. NPP ranges from 2-
3 km m-2y-1 or higher. This high productivity is sustained
despite heavily leached, nutrient poor soils, of the high
composition rates possible in moist, warm conditions. Litter
decomposes rapidly, and rapid nutrient uptake is facilitated
by mycorrhizae which are fungal mutualists associated with
Arctic Tundras have the lowest NPP because of the low
temperatures (below zero degree Celsius). And short
growing seasons in the area; net primary productivity is
very, between 100-200 m-2y-1. Soils are low in nutrients due
to slow decomposition affecting the productivity of thr plants.
• How do humans overcome limitations
imposed by the physical environment on
primary productivity? Cite specific
examples to support your answer.
Removal of weeds
Constant human mitigation