Effects of Brassica rapa on Glycine max (Soybean)
Growth in Cadmium Rich Soil
Kody Massner
Jake Rutan
Zach Shriver
Loras College Department of Biology
1450 Alta Vista Street
Dubuque, IA 52001
Our objective is to determine whether Brassica rapa absorbs enough cadmium to allow
unaltered growth of Glycine max. This study should be funded because the use of Brassica rapa
alongside soybeans and other crops could improve yields by decontaminating the soil in which
they are planted. This is significant due to the increased pollution from waste products that
contaminate the soil and kill crops. We believe Brassica rapa will do this because it has been
shown in other studies that Brassica rapa uptakes heavy metals out of the soil and into its own
tissues. We will test this by planting Brassica rapa alongside soybeans in contaminated soil and
measure the biomass of the soybeans in uncontaminated soil to the biomass of soybeans in high
cadmium soil.
Project Overview
Pollution is a growing concern in today’s world. Not only is it causing global warming,
but many pollutants affect the water we drink and the food we eat every day. One stable crop,
soybeans, are extremely vulnerable to soil containing pollutants such as heavy metals and
demonstrate inhibited growth in such soils. This largely accounts for decreased yield due to these
heavy metals being found in the soybeans. Farmers have been trying to figure a cost effective
way to reduce this problem and clean the soil of these heavy metals.
Cadmium is one of many heavy metals that is found in the soil and affects the growth of
soybeans. One study (Luan et al. 2008) shows how the increase in heavy metal concentration of
Cd, Pb (lead), and As (arsenic) affects the percent germination as well as the root and shoot
growth of soybean plants compared to that of a control with no toxins in the soil. The study
concludes that a greater concentration of heavy metals decreased the shoot growth in soybeans
compared to that of the control (Fig. 1).
showed results of leaf withering when
barium, another heavy metal, was in
high concentrations in the soil. This
Fig. 1 (Luan et al. 2008)
Another study by (Suwa et al. 2008)
confirms that a wide range of heavy
metals affect soybean plants. Two studies show the effects of cadmium specifically on soybean
plants. In one experiment (Casterline and Barnett 1981), soybeans were treated with cadmium of
several different molarities. All of the different soybean samples showed significant growth
reductions, some of which inhibited plant growth of up to 100%. A second study (Huang et al.
1974) found that cadmium reduced pod fresh weight of the legumes by approximately 35%,
2
decreased nitrogenase activity by 71%, and caused a 60% depression in photosynthetic activity.
All of these separate studies show the harmful effects caused by having cadmium and other
heavy metals in the soil and the specific effects they have not only on growth, but also in
germination, nitrogenase activity, and photosynthesis of soybean plants.
Brassica rapa is a species known for its ability to grow and absorb large amounts of the
heavy metal cadmium through its roots from Cd rich soil. This is seen in a study (Ishikawa et al.
2006) where Brassica juncea, a species in the same genus as Brassica rapa, was tested to
determine whether it was suitable for phytoremediation, decontamination of the soil. The study
concludes that Brassica juncea can uptake Cd into its shoots and roots, with as much as 70% of
the Cd uptake being present in the shoots. If a farmer were to have cadmium rich soil due to
pollution from mining and smelting techniques, battery waste, or nuclear facilities, it might not
be cost effective to have a professional crew clean the soil, so an alternative idea would be to use
Brassica rapa to see if it will remove the heavy metals from the soil.
In Iowa and the rest of the Midwestern United States, soybeans are a widely farmed crop
and it is seen that concentrations of cadmium or any other heavy metals affect these crops grown
and the business and livelihood of many farmers in the region. Thus, many farmers are
searching for new ways to fight and rid of pollutants in the soil. Our study questions whether or
not planting the species Brassica rapa with a soybean plant in Cd rich soil will allow the
soybean plant to grow normally as if there was no Cd present. Based on this previous knowledge
we will run an experiment in which Brassica rapa and our soybean plant together with one
another in the same soil. By comparing data of various sample combinations we can determine
whether or not Cd has a negative or neutral effect on soybean growth when the sample contains
Brassica rapa. Our hypothesis is that if Brassica rapa absorbs the cadmium in the soil, then the
3
soybean growth will be unaffected because there will not be a high concentration of cadmium in
the soil for the soybean plant to uptake. We predict that the growth of the soybean plant will not
be significantly decreased.
Materials
Brassica rapa (50 seeds)
Glycine max (200 seeds)
Potting Soil
Cadmium Nitrate Solution
Calcium Nitrate Solution
Pots and planting tool
Digital Balance
Tap Water
Squirt Bottle
Methods
First we will germinate both the Brassica rapa and the soybean plants in two separate
large pots containing potting to ensure an adequate sample size for testing. We will then water
each set of seeds every other day for a two week period in order to allow sufficient time for the
seeds to germinate. This will allow us to take and record a biomass of each individual soybean
plant using a digital balance, which we will later use to compare to masses of each soybean after
contamination. After the two week germination period we will record the masses and then
transplant the soybeans into four planters containing forty soybeans respectively, each with a
different experimental treatment.
4
The first treatment will be the soybean in absence of Brassica rapa in normal potting soil,
which will serve as a control to compare root and shoot growth of the other treatments of
soybeans. This treatment will be exposed to .6g/L calcium nitrate in order to ensure that it isn’t
the nitrate that is affecting the soybean growth. The second treatment will consist of the soybean
alone in contaminated soil. We will contaminate the soil by dousing the potting soil uniformly
with a squirt bottle filled with 2mg/L cadmium nitrate solution, which will ensure that the
cadmium nitrate does in fact hinder the growth of the soybean. The next treatment will consist of
soybeans planted with Brassica rapa in uncontaminated soil to ensure that it isn’t the Brassica
rapa that is stunting the growth or killing the soybeans. The final treatment is the soybeans
planted with Brassica rapa in soil contaminated with the same concentration of cadmium nitrate,
which will allow us to determine whether Brassica rapa is a factor in decontaminating the soil
for the benefit of the soybean plant. In this final treatment we will separate the planter into four
areas dedicated to varying planting times. In one section of the planter we will plant both the
soybean and Brassica rapa at the same time, whereas in the other three areas we will plant the
Brassica rapa one, three, and five days prior to the transplant of the soybeans. Each area of the
final treatment will contain ten soybeans and be treated with the same amounts of cadmium
nitrate. The reason for planting the soybeans at different time intervals is to determine whether
Brassica rapa needs a certain amount of time to adequately extract the contaminants for the
soybeans.
We will allow each separate soybean treatment to grow for a two week period after initial
transplant. At the conclusion of the two week period we will measure and record the final
biomass of the soybeans using the digital balance. This data will compared to the initial
biomasses recorded and compared among experimental treatments in order to determine whether
5
there is a significant difference in the masses. This will be done by using a paired sampled t-test
on SPSS with 95% confidence. If Brassica rapa is effective in extracting cadmium from the soil
we will expect the before and after biomasses to not be significantly different.
6
Literature Cited
Casterline, James, and Barrnett, Neal. "Cadmium-Binding Components in Soybean Plants."
www.plantphysiol.org. Plant Physiol, 17 Dec. 1981. Web
Huang, Bazzaz, and Vanderhoef. “The inhibition of soybean metabolism by cadmium and lead.”
Plant Physiol. 1974 Jul;54(1):122–124. Print
Ishikawa, Satoru, Noriharu Ae, Masaharu Murakami, and Tadao Wagatsuma. "Isa Suitable Plant
for Phytoremediation of Cadmium in Soils with Moderately Low Cadmium
Contamination? - Possibility of Using Other Plant Species for Cd-phytoextraction."Soil
Science & Plant Nutrition 52.1 (2006): 32-42. Print.
Suwa, Ryuichi, and Krish Jayachandran. "Barium Toxicity Effects in Soybean Plants." Arch
Environ Contam Toxicol (2008): 397-403. Print.
Luan, Cao, and Yan. "Individual and Combined Phytotoxic Effects of Cadmium, Lead, and
Arsenic on Soybean in Phaeozem." Www.agriculturejournals.cz. Agriculture Journals, 15
Aug. 2008. Web
7