Photosynthesis: How Does Light Affect

Photosynthesis: How Does Light Affect Soybean Growth?

This experiment deals with how environmental photosynthesis different wavelengths of light affect plant growth. The direct inspiration for this experiment (adapted of course to a student's budget and resources) was a published study in which soybean plants showed that between 14 and 18 days after sowing, it was possible to relate adaptations in photosynthesis and leaf growth to dry matter accumulation. Soybean development under low pressure sodium blue light was similar to that of shaded plants.

(Britz & Sager, 1990, p. 448).

Soybeans grown under blue light will provide results similar to shaded conditions that are conducive for plant growth. Soybean development under blue light conditions will exhibit similar in several respects to that of shaded plants. This is consistent with an important role for blue light photoreceptors in the regulation of growth response to irradiance. In this experiment, three different colors of light will be used to grow plants.

Soybeans under blue light conditions will exhibit relatively mores

This hypothesis is likely to be correct because it has been executed under sodium blue light conditions. Also, the amount of direct sunlight has been kept constant.

Application:

These results will have wide application in greenhouse or low light conditions in temperate zones of planting conditions using non-genetically modified (GMO) legacy seeds in growing organic soybeans in truck garden type of conditions. In the case of a widespread catastrophic failure of GMO plants, legacy seeds could then be grown widely by non-skilled personnel to supplement food rations in low-tech environments without sophisticated technological and in light poor northern regions of the Earth.

Introduction

The relationship between light and plant growth is demonstrated by exposing leaves to various different colors of light. Light supplies the power to carry on photosynthesis, the food-making process in leaves. But the spectrum of light most utilized by a leaf is limited to three distinct colors, red, blue and yellow. Red and yellow have been more documented. Blue light research needs more work, especially to document Northern Hemisphere growing conditions.

Independent Variable: Color of light

Dependent Variable: Plant height and leaf to area ratios.

Control Variables:

1. Same type of soybean plants

2. Same type of fertilizer, soil, water, potting soil, colored filters.

3. 10 gallon aquarium tank truck/small garden conditions.

Procedures:

1. Plant four soybean seeds of in an aquarium containing 5" of well moistened potting soil. Allow to germinate from seeds.

2. Place a colored filter tent over each plant. One filter should be clear. Use blue, yellow, and red film for the other filters. Be sure to construct the frames for the tents from the coat hanger wire to allow for growth in height (at least 2.5 inches on a side). Place the filter over the planted seed.

3. Apply 2 oz dosage of organic fertilizer per plant per day. Be exact and do not vary the dosage.

4. Place the aquarium in direct sunlight. Keep in the same location during the experiment and water daily (2 ounces).

5. Measure each plant on day 14 after planting and record the findings. Record height.

6. Be sure to measure from the bottom of the aquarium and not the surface of the potting soil. This is to take into account the depth of the roots.

Reasoning for Experimental Steps and Justification for Methodology

The steps need to simple to replicate, for purposes of experimentation and for replication in primitive agricultural conditions. This provides the best control and uniformity. Without uniformity, there is no validity in the experiment. Simple and replicable design provides this. If the design is faulty, the experiment can not be replicated and it has no validity. For this reason, this experimenter purposely chose a simple experimental design. Indirect sampling of the leaf canopy will be adequate because it is not dense.

Materials and Conditions:

All the materials for this project were available locally including:

1. 10 gallon aquarium

2. Colored transparency sheets. Coat Hanger Fire for Frames for transparency sheets. Leave 1/4-inch holes in the sides to allow for escape of excess moisture.

3. Legacy soybean seeds were purchased via mail order from Legacy Seeds Inc., www.legacyseeds.com

Experimental Questions to Be Answered

1. How does the amount of white light affect the growth in height (cm) of the plants? White light also includes the blue spectrum so one has to consider it as a control factor.

2. How does each different color light affect the growth in height (cm) of the plants?

3. How does the different color of light affect average leaf-area ratios

Literature Review:

For an indeterminate time in human history going back to ancient China, soybeans have played an important role in human agriculture and today represent a number of successful plant and product applications. Therefore, the plant has historically been and will probably be very important in the same vein. Relevant articles are reviewed below.

In order to understand specifics of soybean growth, general growth of plants has to be understood, especially plant to height ratios. The plant as a whole must be understood to understand individual characteristics. The growth is very fluid and not mechanical. For this reason a holistic approach is necessary (Briggs & Christie, 2002, p. 134). The Briggs and Christie article was relevant to this experiment because it revealed the effect of blue light on blue light receptors in plants (Ibid., p. 204).

In the article by Britz and Sager soybean development under blue light was similar in several respects to that of shaded plants, consistent with an important role for blue light photoreceptors in regulation of growth response to irradiance. Thus, soybeans from blue light conditions partitioned more growth. The leaf starch accumulation rate was higher for both species and starch content at the end of the dark period was three-fold for soybeans, respectively under blue light conditions. Possible relations between starch accumulation, leaf export and plant growth in response to spectral quality were considered as well (Britz & Sager, 1990, p. 448).

The Erickson and Silk article explained the significance of measuring from the tip of the plant root (Erickson & Silk, 1980, p. 4). This is a classic method in plant morphology (Ibid, p. 6). It also discussed the importance not just of measuring longitudinal growth, but also linear growth (Ibid, p.8). The article also illuminated issues of growing complexity of plant growth of the seedling after it penetrates the soil surface as opposed to the growth of the roots (Ibid, pp. 9-11).

Obviously, plant moisture is a critical issue. In the Schuh article, too much humidity adds significantly to plant disease (Schuh, 1993, p. 112). In hot or moist climates, this could be fatal to the plants. This influenced the author's decision to keep the aquarium uncovered and to leave holes in the sides of the tents to allow the escape of humidity. This article also influenced the experimental reliance upon a constant amount of light. Too much leaf wetness would have decreased the plant growth considerably.

In the Briggs and Christie article, the importance of blue light was pointed out in responses in plants including phototropism, chloroplast migration and stomatal opening. The photoreceptors for these light responses have been identified as phototropins, substances exclusive to plants that regulate and mediate plant metabolic processes.

For the processes of the author's experiment, the important component of these discoveries is the unique contribution of blue light to plant growth (Briggs & Christie, 2002, p. 208).