Light wavelength effects on soybean growth and photosynthesis

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.

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).

Threats to Internal Validity

The plants were all in the same environment (a ten gallon aquarium tank) under the exact same conditions of temperature and humidity. They were given the same amount of water and fertilizer and checked on the same date.

Data: Growth at 14 Days

Red

2 cm

Yellow

2 cm

Blue

3 cm.

White

3 cm

Graphic Visual Representation of Growth Relationships in Color vs. Height

Height

Color

Discussion of Graph:

The graph tracks the different heights. Blue light shows better results than red or yellow light. Blue is part of the white light spectrum, so it is understandable that the results would be similar. White light had to be used as a control factor

Conclusion

Soybean development under blue light was similar in several respects to that of shaded plants. It was consistent with an important role in the regulation of growth. Therefore, soybeans from blue light conditions partitioned relatively more growth to leaves than red and blue only. The results confirm the general hypothesis. Experimental design was a key factor in the success of the scientific inquiry due to control and uniformity. The investigation can be replicated due to the ease of acquisition of the experimental materials and the uniformity of conditions. The replication of an experiment is an evaluation of validity because it eliminates chance occurrence as a factor in the results of the experiment. The ability of another (especially others plural) to replicate an experiment an evaluation of validity of an experiment because the more an experiment is replicated, the less of a chance that by of repetition of the same results via luck. Simplicity is key in experimental replication. The materials, measurements and conditions are simple to aid in this.