Effect of Intra specific competition on the Biomass and Height of Helianthus AnnuusAbstract: The purpose of this experiment was to study the biomass and stem length of Helianthus plants growing in an intra specific competitive environment compared to Helianthus growing in an isolated environment. I hypothesized that increased competition would limit the amount of nutrition available to each plant and thus effect the growth potential. A total of 24 plants, 6 to each pot were grown for ten weeks under the same environmental conditions. The plants grown under competitive conditions had only 1/7 the dry biomass and 5/8 the stem length of plants experiencing no competition. The competing plants had an average dry biomass of 1. 54 grams, with a standard deviation of.
41. The average control had a dry biomass of 10. 54 grams and a standard deviation of 3. 95. Analysis revealed a p-value of. 0286, considered significant.
These results suggest that intra specific plants are affected by living in close proximity to one another and I therefore except my hypothesis as correct. Introduction: When plants reproduce, size is highly correlated with reproductive output (Samson and Werk, 1986).
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The struggle for reproductive survival among plants is the struggle to grow in the face of competition from neighbors. So the question this experiment asks is how competition affects the growth of plants. A plant growing in a nutrient-abundant environment free from competition will exhibit maximum growth potential and seed production (Watkins on, 1983).
But as the plant density increases and available resources become more limited, the decision must be made between continued growth or producing viable seed.
I hypothesize that as Helianthus plant proximity becomes tighter, plant size and stem length will be effected negatively. For now my null hypothesis will be that plants grown in isolation will exhibit the same size and stem length as Helianthus plants grown under intra specific competition. Our subject plant for this experiment is Helianthus annulus, a common sunflower plant cultivated all over the world for its seeds and seed oil. Helianthus is an annual plant that grows from 1 to 3 meters, depending on conditions. It is for this reason I chose Helianthus as our subject plant. Shorter plants have a less measurable variable.
Helianthus plants, with their long straight stems, would have a much easier variable to measure. A total of 24 Helianthus plants, six to each pot, will be used in the treatment. The large number of subject plants is because of genetic variation that might sway my results if I were to use only a single treatment pot. I will use stem length and dry biomass as the variable to determine the results of my experiment. A similar experiment was performed on natural communities of Xanthium found off the coast of Maine (Weiner, Kinsman, and Williams; 1998).
Xanthium, which belongs to the same family as Helianthus (Asteraceae), was tested in 5 different plant densities.
Plants growing in tight clumps were, on average, one-quarter the size of isolated plants. The authors determined that competition was a major factor in determining plant size. Methods & Materials: I began my experiment by picking about 44 of the healthiest looking Helianthus seeds supplied by the Cal State Fullerton Greenhouse. The soil and pots were also provided by the greenhouse. The pots were roughly 3″x 3″x 5″ in size. The fertilized soil was packed into the pots about 1″ from the rim.
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Ten seeds were placed into the soil of each one of the treatment pots spaced equally form each other. Although I wanted six seeds to grow in each treatment pot, I wasn’t sure they would all germinate. So I used ten seeds per pot to increase my chances of six germinating. If any extra plants grew they were quickly removed. The seeds were then packed tightly with another half inch of soil.
The pots were marked “6” on the side of each one for identification, Water was poured slowly and gently to prevent the force of the water from raising the seeds back to the surface. The control pots were prepared in the same manner, except only two seeds per pot. It took four days for the seeds to germinate. An average of 8 plants germinated in each treatment pot, but these were quickly thinned out. At first, the plants were watered only twice a week. But as they progressed in size, waterings were done on a daily basis.
The stem lengths were measured once every week. The lengths were measured to within. 1 centimeters and were taken from the base of the stem to the top of the last node. By the end of the tenth week, the flowering plants were harvested. Their final stem lengths were measured and the plants were then removed from the soil, roots and all. The soil was shaken from the roots and were individually placed in marked paper bags with one end open.
The plants were allowed to dry in the greenhouse for ten days. The dried out plants were then weighed to within. 01 grams. The average dry biomass was determined by taking the total mass of all the dried plants and dividing by the number of plants weighed. Average lengths were determined in the same manner. The p-value was determined using the Mann-Whitney Test.
Results: On average, The control plants had seven times more dry biomass and 50% more stem length than the densely-packed, treatment plants (See Graphs 1 and 2).
The control plants had an average dry biomass of 10. 54 grams, with a standard deviation of 3. 95.
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Vascular or nonvascular? My plant is vascular because it has true roots, stems, and leaves. It has a system for transporting food and water. My plant has tube –like structures that provide support and circulate water and food throughout the plant. Monocot or Dicot? My plant is a dicot because it’s flowers have either four or five petals or multiples of these numbers. The leaves are wide with ...
The competing plants had an average dry biomass of 1. 54 grams, with a standard deviation. 41. The p-value for this experiment was. 0286, considered significant.
Conclusion: With a calculated p-value of. 0286, the results of this experiment are significant. Therefore, I must reject my null hypothesis and accept the alternative hypothesis that an increase in intra specific competition causes a decrease in plant size and stem length. There were noticeable differences between my treatment and control plants.
The control plants developed long, thick, straight stems with a healthy, green color. The stems of my treatment plants were thinner, shorter, and contained a yellowish tint, possibly early chlorosis. The treatments stems were also bent around in every direction away from the pots, probably an attempt to find more light exposure in the sunlight-limited space. By the time of harvesting, seeds were visible in both treatment and control plants.
Despite limited resources, the treatment plants hade allocated scarce nutrients to its reproductive rather than photosynthetic tissue (Weiner, 1990).
The plants sacrificed their own potential growth in order to ensure their offspring’s survival. However, some treatment plants that did not produce any seeds still had the same biomass and stem length as treatment plants that did produce seeds. This might be explained by resource limitations so tight that only enough were available for the plants own survival.
As the experiment progressed, I noticed the treatment plants were growing in an area of the greenhouse that was not exposed to daylight as long as the controls. This automatically put the treatment plants at a disadvantage from day one. I tried to correct this error by rotating the treatment plants closer to the sunlight. But the control plants had already developed a height advantage by that point. I don’t feel this discrepancy would have changed the outcome of the experiment, but might have affected my results. I think the next big step up from this experiment should be to determine the plant density that maximizes plant size while minimizing land usage..
