The Effect Of Plant Population Density Biology Essay


In recent times, a growing global population has beckoned for increased food supplies. Meanwhile, conventional agriculture is being found to be unsustainable and ecologically detrimental. For example, 38% of the endangered species in the United States are affected negatively by current agricultural practices (Bianchi, 2006). The usage of artificial fertilizers and extremely intensive harvests has both led to degradation of soil as well as eutrophication as the degraded soil washes out into bodies of water. Synthetic pesticides and herbicides contaminate the environment, while irrigation techniques divert water away from natural habitats. Conventional agriculture is overall very resource- and land-intensive and taxing to the environment, eventually adversely impacting society; in the long run, it will be unable to balance a harmony between nature and human needs.

As a consequence of the potential effects of conventional agriculture, methods of sustainable agriculture are fast being developed and implemented. Sustainable agriculture must be implemented with the calculation of the maximum potential yield of food without harming the people and animals that eat it, and without disturbing the balance between society and the environment with conventional but widespread methods such as pesticides. In this sense, sustainable agriculture must be used in a method that would make the most efficient use of resources without straining the environment. A key crop for which this problem must be solved is wheat, which accounts for at least 20% of the total food calories consumed by humanity and has been rooted for thousands of years as a staple food (Langer & Hill, 1962). This crop has a multitude of uses besides as food; it is one of the most valuable plant species in the world (Diamond, 2002).

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An agricultural method that can aid towards maximum sustainable efficiency and land conservation is the determination of the maximum product usable by humans from crops through the optimization of the population density of a crop. The growth of the common wheat Triticum aestivum, like other plants, is heavily influenced by hormones such as auxins, giberellins, and cytokinins in terms of growth, genetic expression, and other characteristics. Furthermore, such hormones have other functions in this specific plant. For example, it has been found that gibberellic acid promotes the growth of hypocotyls and seed germination, important in enlarging seed yields usable by humans (Khan & Zulfiqar, 2001). These hormones require nitrogen and other chemicals that have to be derived from the soil in addition to carbon from photosynthesis (Davies, 2010). With increased plant population density, however, individual plants must compete more for the resources required for these hormones in addition to those needed for actual development, such as light and water. At the same time, it is known that auxins, a major class of growth hormones, accumulate in dark areas, for instance in situations where a plant is shorter than surrounding ones, and stimulate further growth (Briggs, 1963). A cycle could then occur in densely populated areas where plants continuously grow taller over each other and compete for light for photosynthesis, but it is uncertain to what extent this would be done considering the limited resources of the soil. Meanwhile, in more sparsely populated areas, there is less competition, and plants may grow more slowly and with a wider shape as auxins accumulate less and fewer resources are diverted to the production of auxins, other hormones, and competitive stem growth. Because of these possible different allocations of resources according to variations in population densities, there may be varying amounts of yield, such as the calories of wheat grains usable by humans. Still, there is no exact data concerning these. The exact effects and extents of population density on the growth and usable yield of the common wheat, Triticum aestivum are to be investigated in this study, in terms of plant height, width, and energy evolved from the wheat grain of each plant.

The significance of this experiment is that wheat is a very important staple food to the whole world. Wheat is a part of the grain group, and humans need a large amount of grains everyday in their diet. Because wheat is a very important and large part of a human’s diet, many countries need to farm wheat by growing wheat efficiently. However, little research or experiments have been done on the common wheat relative to maize and other plants. In this sense, conducting this experiment will help the world with better methods of growing wheat and with how to use land more wisely for more efficient yet sustainable production of wheat and conserving the soil better for future growth of plants.


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There are to be multiple small, planar plots of land with the same area, all located in the same region with the same amounts of sunlight, water, soil, and other resources necessary for a plant. All resources should be of sufficient quantity and quality to allow plants to feed, photosynthesize, and develop in a more-or-less proper manner; however, they should be controlled so that each plot receives the same amount of each. Resource replenishments should be given periodically and at the same points in time for all plots. Each plot of land is to have a different population density of Triticum aestivum, with plants evenly spaced in a uniform pattern. To ensure that plant densities do not unexpectedly deviate, such as through failed germination, seedlings should be planted simultaneously, then germinated and grown for several days in a single separate area, and then transferred into the designated experimental plots all at the same time to have all population densities start and develop at the same time. After set periods of time up to full maturity, the average heights and widths of the plants are to be measured systematically. Height measurements should be done based on stem lengths in their natural positions perpendicular to the soil plane, but without stretching the stem to maximum vertical length (Heady, 1957). To measure width, the length between the tips of the two bottommost leaves of each plant should be measured. When full maturity is reached for all plants, which should occur 120 to 145 days after germination, the wheat in each plot should be harvested separately and the grain extracted and stored in different volumes for each population density (Triticum aestivum, wheat, 2009). Afterwards, each volume of grain should be combusted fully inside a calorimeter and the energy evolved from the combustion should be recorded to quantify the potential yield usable by humans as food. All measurements should be classified into the different population densities.

Anticipated results:

It had been found previously that for maize plants, there is a critical level of population density above which yield per plant is adversely affected (Modarres, 1998). As maize and Triticum aestivum are in the same family, a similar result would be expected where increasing population densities lead to a somewhat sudden drop in energy evolved per plant. A similar experiment with common wheat also found that increased population density resulted in fewer wheat ears per plant, further supporting that notion (Nerson, 1980). However, it is unknown if there is varying energy per unit of mass in grains per different plant population.

The lack of competition between plants in areas with low population densities would result in abundant resources for each plant, but no need for high vertical growth because plenty of light is already received. Therefore, they still grow, but rather more horizontally, and resources can be directed to other uses such as producing grains. In the meantime, plants in higher population densities would face more competition to grow vertically. The horizontally extending leaves of each plant in higher densities would block each other’s light and this accumulates auxins, which accumulate in less illuminated areas, in the shorter plants (Briggs, 1963). This hormone and others in turn stimulate the plants to grow taller, and as each plant does so, every other one increases their heights to keep receiving light. However, the lack of resources to each plant in this situation and the diversion of most of them to concentrate on vertical growth would create a dearth in horizontal growth. Also, when there is not enough light for a plant, there could be a lesser ability to produce these hormones and other chemicals such as cellulose, required for growth in Triticum aestivum. Therefore, when plants start blocking light in significant amounts from each other, some plants could suffer and the differences in height, width, and yield among those plants would increase.

To summarize, higher plant population densities would result in taller but narrower plants, with less yield per plant, with the opposite for lower plant population densities.

Conclusions and significance of anticipated results:

The anticipated results that increasing plant density increases the amount of common wheat (Triticum aestivum) yield per plant and decreases grain yield suggest that decreasing plant density will increase grain yield. This information could help farmers to try to find an efficient balance between high yield per plant and a high wheat population, where the product of plant population and grain yield per plant would be the highest as possible. In addition, the highest product can be derived from crops while using less land and soil. Thus, there is space for more crops to grow as well as less impact done to surrounding ecosystems and environments for a similar amount of usable product. Also, using the land in moderation will mean that the soil will be used in moderation and not depleted to such an extent that the land will become degraded. Therefore, lands will maintain richness with the ability of allowing plants to thrive in future generations. This study may motivate further research. For example, developing a technique in which wheat plant density and grain yield both increase. One of the ways of achieving this may be genetically enhancing yield, for example by locating a gene controlling embryo growth. Another possible research path can be determining how plant growth hormones can be influenced or produced more to positively affect plant yield. Furthermore, if root lengths of plants were to be increased, individual plants would be able to utilize more soil from deeper areas, and thus yield could be increased even with higher population density. Comparison of the experimental results on Triticum aestivum with other important agricultural species, perhaps even livestock, would be important as well. Also, since varying environments affect organisms differently, it is crucial to research the effects of plant population density in various parts of the world. In a time where the world’s human population is growing and conventional agriculture is being found to be damaging and unsustainable, finding an inexpensive and easy-to-implement combination between agricultural efficiency and sustainability are key points in aiding global economies and societies as well as the Earth’s environment; one step in this is finding optimum population densities with respect to food yield. With sustainable efficiency in farming, the Earth will be able to better support the growing population of the world, perhaps with an increased carrying capacity.

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