Ad. Biology, Period G
Interspecific and Intraspecific Plant Competition
A study was conducted to address the problem of interspecific and intraspecific competition among wheat and mustard plants. It was hypothesized that increasing the plant density, and therefore increasing intraspecific competition, would negatively impact the plant biomass. It was also hypothesized that interspecific competition would have a stronger negative effect on the plant biomasses. This was tested by planting varying numbers wheat and/or mustard plants in pots, and measuring their biomass. The data confirmed the above hypotheses. Findings suggest that intraspecific competition and increasing plant densities had a negative effect on plant biomass, however, interspecific competition had a more severe negative effect. The future study of this topic could allow for greater agricultural success by developing new means of spacing plants, and fertilizing them to combat intraspecific competition. This could also allow for a greater understanding of how to combat interspecific competition in agriculture.
Before testing began, the researcher hypothesized that if intraspecific competition was increased, than it would have a negative impact on the overall biomass of the plants, however, if the amount of plants involved in intraspecific competition per pot increased, than the biomass would be more greatly negatively impacted. If interspecific competition increased, than it would have a stronger negative effect on the plants involved in it, even in lower densities. However, the researcher postulated that if plant density increased, than it would also have a negative effect on the overall biomass of both plant species.
Materials and Methods
• 42 equal, 4 inch pots
• Artificial soil mixture
• Mustard seeds
• Wheat seeds
• Tray (to hold pots)
• Supplemental light source
• Scissors (for weeding)
• Data sheet
• Razor blade
• Electric balance
• Graduated cylinder
1. The plants were labeled by section, pot number, and number of mustard and/or wheat plants
2. Each 4 inch pot was filled with soil, which was then packed down to ½ inch below the rim.
3. The required number of seeds for each treatment was counted out. A few extra were added to ensure that enough seeds would germinate.
4. The seeds were evenly distributed over the soil surface, and covered with ¼ of an inch of potting soil.
5. The pots were then checked for uniformity of soil amounts.
6. The pots were put in the supplied tray, and placed under a supplemental light source. They were then routinely watered (50-75mL)
7. After one week, the number of plants was counted. Any extra plants were carefully cut with scissors as close to the soil as possible. The plants were then periodically checked for extra growth, and any that occurred was removed.
8. The weekly condition of the plants was checked and observations were recorded.
9. Prior to harvesting, the total number of plants in each pot was recorded.
10. A razor blade was used to cut the plant shoots off at soil level. A balance was used to determine the biomass of the required species.
11. The per plant biomass was then calculated for each pot
12. The average per plant biomass was calculated for the pots with only one plant species
13. The standardized per plant biomass was then calculated for each pot by dividing per plant biomass by the average biomass.
There were multiple variables in this experiment. The controlled variables included the size of the pots used, the quality and amount of soil placed in each pot, the amount of light each plant received, the amount of water each plant received. There was no control group in this experiment. The dependant variable was the amount of plant growth, and the independent...