Primary Productivity in a Grassland Ecosystem

Alfante, MonicaCuebillas, Arkin

Malabanan, PaulineMane, Jon

Llamas, Patricia

A. BIOLOGICAL MASS

– mass of organisms per unit area of ground time

-also known as biomass

B. PRODUCTIVITY• 1. PRIMARY PRODUCTIVITY – the rate at which

primary producers assimilate solar energy in a community

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 sugar

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 PRODUCTIVITY• 1. TEMPERATURE – regulates the rate of physiological

processes and influencing growth and developments of plants

• 2. WATER – Water is required by all living organisms . Plant can be stressed by lack of moisture as well as an excess moisture.

• 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.

D. SUCCESSION • -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.

OBJECTIVESA.Measure the net primary

productivity in different micro habitats of a grassland ecosystem.

B. Understanding the factors affecting or limiting primary productivity in grassland.

MATERIALS• Bamboo sticks • Meter Sticks• Old newspapers• Plastic string• Scissors• Triple Beam Balance

PROCEDUREA. 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 boundaries.

• 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 micro site.

• 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 vegetation.

• 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 subsample properly.

• 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 be removed.

GUIDE QUESTIONS• Why was the vegetation cut at the

start of the experiment? 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.

GUIDE QUESTIONS• 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 biomass weight.

• Explain the difference in NPP between the two microhabitats.

NPP in the open region is higher than in those in shaded.

GUIDE QUESTIONS• Do you think the NPP in these

microhabitats remain the same for the whole year?

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.

GUIDE QUESTIONS• 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)

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.

GUIDE QUESTIONS• 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 plant roots.

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.

Adding fertilizer Removal of weeds Adding pesticides Constant human mitigation supervision

Sources• Answers.yahoo.com/question/

index/qid=20081017163958AAeaWwp

• Oregonstate.edu/dept/eoars/sites/default/files/publication/328.pdf

• www.montana.edu/hansen/documents/bio494/slides/Lec4.pdf

• www.nature.com/sctiable/knowledge/library/terrestrial-biomes13236757