Salicornia europaea Root Exudate and Soil Mobility of
Metallic Ions
TABLE OF CONTENTSIntroduction…………………………………………………………………Page 1Materials and Methods...……………………………………………………Page 2Results………………………………………………………………………Page 5Discussion…………………………………………………………………..Page 6Acknowledgements…………………………………………………………Page 8Literature Cited……………………………………………………………..Page 8
INTRODUCTION
Phytoremediation, the ability of plants to remove toxic and nontoxic metallic ions from
soils (Salt et al. 1995: McIntyre 2003: Pedro et al. 2013). It offers a cost effective method in
which plants like glasswarts or saltwarts are used to aid in the goal of phyto remediating the
contaminated soil (McIntyre 2003).Salt Warts and Glassworts are halophytes typically found in
saline environments and Salicornia is a commonly found glasswort that displays consistent
success in studies involving phytoremediation of toxic materials and also toxic metals from
contaminated soils (Salt et al. 1995). �
Salicornia are not only pioneer plants that grow on beaches, sand and salt marshes but
they are also edible – can be cooked or raw- and the ashes of these glasswort are used in
glassmaking and soap making – LeBlanc process. It can also be used to produce animal feedstuff
and as a biofuel feedstock on coastal land where conventional crops can’t be grown (Fig.1).The
study focuses on the Rhizosphere - the narrow zone of soil immediately surrounding the root
system – compounds secreted by plant roots serve important roles as chemical attractants and
repellants (Fig. 3). Through exudation of compounds, roots regulate soil microbial in their
vicinity, and change chemical and physical properties of the soil. (Walker et al. 2003). �
Some studies specifically focused on nontoxic metallic ions such as Copper that are
naturally measured as plant nutrients and measured the plants ability to extract these ions from
the soil. To measure the extraction of these ions, the Copper would be incorporated along with
the root exudates of the Salicornia. The root exudates with the Copper ions were investigated
using an excitation emission matrix (EEM) fluorescence spectroscopy (Pan et al. 2011). These
studies indicated Salicornia plays a role in the movement of essential nutrient ions as well.
The goal of this project was to determine if soluble iron ions can form complexes with
high molecular weight root exudates of Salicornia. The results will aid in the understanding of
the role that Salicornia plays in the mobility of Iron in saltmarsh soils. It is hypothesized that if
Salicornia plants are exposed to soluble Fe (III) then these ions will be incorporated into root
exudates and available to quench fluorescence of exudates.
MATERIALS AND METHODS
To imitate the environment of the Salicornia, 3 trays of 50 samples each were made filled
with a mixture of peat moss and sand (Fig. 4 and 5). The reason for the use of peat moss and
sand was not only because it was the closest to the marshy environment but also because the
nutrient heavy peat moss was balanced by the sand, in a mixture where the ratio was 1:1. Each
sample was sprinkled with Salicornia seeds and was given a 14 weeks to grow. Again to imitate
the natural environment, the trays were watered with a .30 molar solution of Sodium Chloride.
After the Salicornia were grown, they were individually removed from their trays for
their roots (Fig. 6).The roots of the Salicornia will provide the root exudates that will be stored in
individual containers and then put into an ultrasonic bath. The roots were removed and carefully
washed on a petri dish with a wash bottle until the dirt was rinsed off of the roots (Fig. 7 and 8).
After washing, the roots were snipped off and put into a capsule filled with distilled water. The
Containers of root exudates will be placed into 200 ml of distilled water and will be given 3-5
minute cycles (Fig. 9).
After the bath, the extract will be evaporated at 30 degrees Celsius until there is about 10
ml of water. After the root exudates have been carefully collected, they will be placed into
cuvettes which will be placed into a Spectrometer. The exudates will be tested at both 405 nm
and 500 nm to observe fluorescence with multiple samples collected from each trays (Fig 10).
RESULTS
After experimentation and observing the fluorescence of each solution we focused on the
peaks of each of the wavelengths. The peaks indicated which solution of the three tested showed
the most fluorescence. The more the fluorescence the less the quenching and the goal was to
observe more or similar quenching by the Iron Solution as that emitted by Copper Solution.
Looking at both graphs for 405 nm, it is seen that the Control which contained no solution
emitted the most florescence as expected at .14 RFU (Relative Fluorescence Unit) and then
below that came the fluorescence from the Iron Solution at .10 RFU and finally came the Copper
which quenched the most at .08 RFU (Fig. 11 and 12).
The same test was run again with a different sample of exudates from all three
solution but this time they were tested on 500nm on the SpectroVis. Just like the 405 nm the
results were surprisingly similar with the control test giving out the highest fluorescence of .75
RFU which is significantly higher than that observed at 405 nm (Fig. 13). The Iron again came I
second with a peak of .72 RFU a little lower than the control and then the Copper, as expected
quenched the most at .5 RFU (Fig. 14 and 15). The pattern continued as more samples were
tested and it was clearly seen that Iron was quenching some of the fluorescence from the
Salicornia exudates but it was not as much as the Copper was able to quench.
DISCUSSON
Quenching of Copper and Iron were observed at both 405 and 500 nm but the quenching
of the Iron was not as much as that of the Copper. The results still illustrate how Salicornia is an
often forgotten part of the environment, yet it provides so many uses, one being that of
phytoremediation of nutrients in soil. The ability to do such a thing provides endless possibilities
of where to go in the future. Future tests could involve different nutrients that are necessary for
any type of soil. More importantly on further tests, the technique of obtaining the root exudates
will be perfected so that no exudates are wasted or washed off from the rhizosphere.
It is speculated that the observed quenching may be the result of chelation of the iron ions
by high molecular weight exudates in a manner similar to that reported in the literature for
copper. After being tested multiple times, the fluorescence each time of all the exudates
decreased over time and this could have been due to the plants themselves physically dying or
due to no more nutrients being available to be complexed.
There could have also been possible phenolics that directly solubilize the insoluble Fe in
the rhizosphere soil by its reducing and chelating ability. Under conditions in which there is a
Iron deficiency in soils, grasses, cereals and rice secrete phytosiderophores into the soil, a typical
example being deoxymugineic acid. Phytosiderophores have a different structure to those of
bacterial siderophores and their latter bidentate function provides them which a high selectivity
for iron (III).
ACKNOWLEDGEMENTS
The authors of this paper would like to thank their science teacher for his expertise as
well and members of the science department for assisting in the project and for answering any
questions asked of them and would also like to thank the district for providing the school with a
greenhouse in which this project was conducted in.
LITERATURE CITED
BADRI, DAYAKAR R., and JORGE M. VIVANCO. "Regulation and Function of Root Exudates." - BADRI. Blackwell Publishing, 6 Feb. 2009. Web. 09 Mar. 2016.
Doussett, Sylvie, Jean Morel, Astrid Jacobson, and Gabriel Bitton. "Copper Binding Capacity of Root Exudates of Cultivated Plants and Asso." Ciated Weeds. Original Paper, 21 Aug. 2001. Web. 09 Mar. 2016.
McIntyre, Terry. "Phytoremediation of Heavy Metals from Soils." - Springer. , 28 Jan. 2003. Web. 06 Feb. 2016.
Pan, Xiangliang, Jianying Yang, Daoyong Zhang, and Xi Chen. "Cu(II) Complexation of High Molecular Weight (HMW) Fluorescent Substances in Root Exudates from a Wetland Halophyte (Salicornia Europaea
L.)." Cu(II) Complexation of High Molecular Weight (HMW) Fluorescent Substances in Root Exudates from a Wetland Halophyte (Salicornia Europaea L.). , 17 Sept. 2010. Web. 06 Feb. 2016.
Pedro, Carmen A., Marcia S. Santos, and Susana M. Ferreira. "The Influence of Cadmium Contamination and Salinity on the Survival, Growth and Phytoremediation Capacity of the Saltmarsh Plant Salicornia
Ramosissima." The Influence of Cadmium Contamination and Salinity on the Survival, Growth and Phytoremediation Capacity of the Saltmarsh Plant Salicornia Ramosissima. Elsevier, 18 Sept. 2013. Web. 06
Feb. 2016.
Salt, David, Michael Blaylock, and Burt D. Ensley. "Phytoremediation: A Novel Strategy for the Removal of Toxic Metals from the Environment Using Plants." Nature.com. Nature Publishing Group, 1995. Web. 06 Feb.
2016.
Schnoor, Jerald L., and Louis A. Light. "Phytoremediation of Organic and Nutrient Contaminants." - Environmental Science & Technology (ACS Publications)., 1995. Web. 06 Feb. 2016.
Sharma, Anubha, Ita Gontia, and Pardeep Agarwal. "Accumulation of Heavy Metals and Its Biochemical Responses in Salicornia Brachiata, an Extreme Halophyte." Taylor & Francis., 6 July 2010. Web. 06 Feb.
2016.
Walker, Travis S. "Root Exudation and Rhizosphere Biology." Plant Physiology 132.1 (2003): 44-51. Http://mncmicroherders.org/. 2003. Web. 9 Mar. 2016.
Wu, Jianyong, Foo Tim Chau, and Lin Dong Lin. "Ultrasound-assisted Extraction of Ginseng Saponins from Ginseng Roots and Cultured Ginseng Cells. Ultrason Sonochem 8:347-352." Ultrasound-assisted Extraction of
Ginseng Saponins from Ginseng Roots and Cultured Ginseng Cells. Ultrason Sonochem 8:347-352 (200): 347-52. ResearchGate. Nov. 2001. Web. 6 Feb. 2016