Plant competition lab:
Objectives
In this lab, we will conduct an experiment to test both interspecific competition (between radish and collards plants) and intraspecific competition (radishes competing with radishes, or collards competing with collards). To determine if competition is occurring, we will measure survival, plant height, and aboveground biomass. Once the lab is completed and the data are collated from the entire class, you will then need to make graphs and answer the questions at the end of the lab.
Procedure:
Take 9 pots. Use only pots of the same shape (square or round); do not mix types.
Fill the pots with soil to within ½ inch of the top.
Thoroughly water the soil (until it runs out the bottom).
Add more soil if necessary to bring up the level to within ½ inch of the top.
Place the appropriate number of seeds on the soil surface. Be sure the seeds are evenly spaced. In the mixed species pots, intersperse the two species. See the table below for the nine different treatments.
Cover the seeds with a thin layer of soil. DO NOT water the soil again.
Label the pot with your name and the treatment on a piece of tape.
Before harvesting any plants in a pot, collect the following data:
Number of surviving radishes
Number of surviving collards
Average height of surviving radishes (cm)
Average height of surviving collards (cm)
2. After counting and measuring surviving plants, clip each plant where the stem meets the soil. If your pot is a mixed-species treatment, separate radishes from collards.
3a. For single-species treatments:
Weigh all plants within a pot for the total aboveground biomass (g)
Divide the total aboveground biomass by the number of plants that were alive in the pot, to calculate the mean aboveground biomass (g per plant)
3b. For mixed-species treatments:
Weigh all the plants of each species separately, for total aboveground biomass (g) for each species
For each species separately, divide the total aboveground biomass by the number of plants of that species that were alive in the pot, to calculate the mean aboveground biomass (g per plant, within a species)
Experimental Design
Single-species treatments (intraspecific competition tests)
4 collard seeds
16 collard seeds
36 collard seeds
4 radish seeds
16 radish seeds
36 radish seeds
Mixed-species treatments (interspecific competition tests)
2 collard + 2 radish seeds (4 total seeds)
8 collard + 8 radish seeds (16 total seeds)
18 collard + 18 radish seeds (36 total seeds)
Your mixed-species seeds should be arranged in a Latin square design, as shown below (the immediate neighbors of each seed are the other species).
--> Questions to consider about this lab
A. Hypotheses:
B. Which treatments are the controls and which are the experimental treatments?
C. What are the replicates in this experiment? How many are there for each treatment?
D. Do you see any inherent sources of bias in this experimental design?
E. Are there any problems with the experimental design that you can identify which might make interpretation of the data difficult or impossible?
