Required Practical 9 - A laboratory based investigation of the effect of competition on seedling growth

What is the apparatus for this experiment?

Same type of seeds

Forceps

Agar jelly

Petri dish

Water

Weighing scale

What factors do you control in this experiment?

Same species of seed

Same volume and composition of agar jelly

Same amount of water provided

Same light intensity and duration

Same temperature and humidity

Same container size

Same temperature

Describe the method for this reaction

Get five petri dishes with Agar jelly. Each petri dish will have a different number of seeds, from 1,4,9,25 and 36. Use a whiteboard marker to mark the position of each seed on the bottom of the petri dish so that each seed is equally spaced from the other. Measure the empty petri dish with the agar jelly on a weighing scale.

Use forceps to place seeds on the surface of the agar at equal spacing.

Remeasure the petri dish with the seeds, and calculate the difference to get an initial mass.

Repeat steps 1 and 3 two more times so an average value can be calculated at the end.

Record seedling height and root length at regular intervals for a month

After a month, retrieve seedlings from dishes and measure:

Root length

Fresh biomass

Dry biomass

Final height

Place those measurements in a table

Calculate mean values for each competition level

Calculate percentage growth or percentage

Compare growth between groups using statistical tests like t test

Plot a graph of competition level vs. seedling growth.

Why does the growth decrease as competition increases?

As number of seeds per petri dish increase, less growth of the seeds due to intraspecific competition: competition between same species

Thus, more competition for nutrients, food, water and space

The results are usually calculated in percentage (percentage of germination or growth) allowing for comparison between petri dish that have different number of seeds

How do you calculate sowing density?

number of seeds/area of petri dish

What are the potenial issues in this practial?

Contamination: using forceps prevent contamination of bacteria or mould which can kill or compete with seeds

No repeats or statiscal data

Only one species of seeds (intraspecific competition)

Artificial and laboratory condition thus they might not compete the same in natural environment

Control light intensity, water volume, humidity, temperature

Control agar concentration, water, ph, nutrients in the agar (or in soil)

Careful with using biomass to equate successful growth of seedlings. Excess soil/water/agar may be on seeds and skew results