Effects of Intraspecific Competition on Brassica Rapa Growth

Abstract

In this experiment, intraspecific competition was tested which is when members of the same species compete for a same resource. The experiment tested was to see if intraspecific competition using differing densities affected the growth rate of Brassica rapa plants. Brassica rapa are a type of mustard plant also considered the “fast plants” because they grow within a 6-12 week period. They were used for this experiment due to their fast and easy growing process. Past experiments were observed beforehand and according to those, one density would further the survival rate more than the other.

The Brassica rapa seeds were planted and observed over time to study the growth rates between a high and low density. The lower density was expected to have the higher survival and growth rate before starting the experiment. The findings in this particular experiment came out to show extremely similar results to previously tested experiments. While the height did not differ between high and low densities, the survival rate and number of flowers produced was significantly different.

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Introduction

Competition plays a huge role in life’s organisms, especially when it comes to plants. A more specific type is intraspecific competition, in which members of the same species compete for the same resource, which is what this experiment involves. Intraspecific competition is important because when plants of the same group are competing for the same resources in the same living place survival rate can decrease greatly, their need for the immediate resource may run out due to other competing members (Aspbury et al.

, 2013). The purpose for compiling this experiment was to determine if this intraspecific competition affected the growth and development of the Brassica rapa plant at differing high and low densities. The Brassica rapa was used because it can be easily tested, and completes their life cycle within six weeks after planting (Aspbury et al,. 2013). Predictions could be made based off past experiments that used Brassica rapa as well. According to these similar experiments one would conclude that the high density seeds produce less plants, however seem to produce a greater biomass (total mass of once living material) amount. Whereas low density would do just the opposite and produce a lower biomass level going on to produce a larger number of flowers, increase in height, and so essentially obtaining a greater survival rate than that of the higher density. The hypothesis states that the low density would essentially have a higher growth and survival rate than that of the high density. Of course all these experiments differ in terms of density variability, but all testing the same issue of high vs. low density on Brassica rapa.

Methods

The experiment involved the following steps:

1. Seed Selection: Brassica rapa seeds were chosen for the experiment due to their fast growth characteristics.
2. Treatment Setup: Two treatments were established, one with low plant density and the other with high plant density. Low-density pots contained two seeds, while high-density pots contained ten seeds.
3. Planting: The pots were filled halfway with Miraclegro potting soil. Six fertilizer balls were added to each pot, followed by sufficient watering to moisten and compact the soil. The remaining soil was added, and the pots were watered again.
4. Seeding: Small holes were made in the soil for each seed, ensuring even spacing. Seeds were covered with soil, and pots were watered once more.
5. Labeling and Placement: Pots were labeled according to their density (low or high) for easy identification. The pots were placed on a layer of gravel in a plastic container filled with water to maintain adequate moisture. A warm light source was provided, maintaining a distance of 6-8 centimeters from the pots for optimal growth conditions.
6. Data Collection: Weekly observations and measurements were recorded for plant height, number of flowers (pods), and density.

Results

The results of the experiment revealed the following key findings:

Mean Proportion Surviving:

From our analysis after three weeks, our results indicated there was a significant difference in proportion surviving between the low-density and high-density treatments (unpaired t test: t: 4.908, DF=499.451, P= .0001). Plants in the low-density treatment had significantly higher proportion surviving than those in the high-density treatment.

Mean Flowers Per Plant:

From our analysis after four weeks, it was found that there was a significant difference in the average amount of flowers per plant between the low and high-density treatments (unpaired t-test: t= 3.748, DF= 353.359, P= .0001). Plants in the low-density treatment had significantly more flowers per plant than those in the high-density treatment.

Meant Plant Height:

From our analysis after six weeks, our results indicated there was not a significant difference in mean plant height between the low and high-density treatments (unpaired t test: t= .020, DF= 410.77, P= .984). Plants in the low-density treatment had nearly the exact same mean plant height than those of the high-density treatment.

Discussion

The lower density was expected to produce more surviving plants and according to the recorded results it did, as well as produced more numbers of flowers. These results support the hypothesis that states the plants under low density conditions would survive better over plants under high density conditions. This basically means that Brassica rapa plants survive better under lower density conditions. On the other hand, the height stayed relatively the same for both high and low density trials, therefore the null hypothesis was partially accepted. (Miller, 1995). While the height did stay the same for our plants alone an unusual finding was discovered. In comparison to the other classes that did this same experiment, height levels differed in that the Wednesday 2-5 pm class had an overall much lower measured height. This could be due to a number of things such as different amounts of light received, or even not being watered as frequently as the other classes. Other outside studies, which dealt with intraspecific competition, show that it highly affects plant size as well as number of leaves (Shahid et al., 2009). Number of leaves in this case, could correspond with number of flowers on the Brassica rapa plant. The findings in the experiment prove how much the plants were essentially affected.

Conclusion

In conclusion, the experiment demonstrated that intraspecific competition significantly affects the growth and survival of Brassica rapa plants. Low-density conditions led to higher survival rates and increased flower production, supporting the hypothesis. However, there was no significant difference in plant height between the low and high-density treatments, suggesting that intraspecific competition primarily influences survival and reproductive aspects of these plants.

Literature Cited

• Aspbury, A.S., Gabor, C.R. 2013. Laboratory Exercises for Organismal Biology. 15-19
• Miller, T.E. 1995. Evolution of Brassica rapa Populations in Interspecific and Intraspecific Competition, Evolution. 49. 1125-1133.
• Shahid, S.S., Waqar, A., et al. 2009. Intraspecific Competition and Aggregation in a Population of Solanum Forskalii Dunal in a Semiarid Habitat: Impact on Reproductive Output, Growth and Phenolic Contents, Pak. J. Bot. 41. 2751-2763.