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.

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