P1 - Arundo donax L. Candidate for selection re: Metals and Saline Conditions

Today, we will be doing a brief review of the Giant Reed (Arundo donax L.) as a potential candidate for effective heavy metal remediation. This will be the first in a series of mini-articles on interesting candidates for various contaminants of interest based on the series: Phytoremediation: Management of Environmental Contaminants, volumes 1-6 by Abid A. Ansari, Sarvajeet Singh Gill, Ritu Gill, Guy R. Lanza, and Lee Newman (eds.). I selected this series since it’s one of the few comprehensive evaluations of plants with documented microbial and fungal symbiosis for specific contaminants of interest that also includes actual field data for pilot implementation. This interests me. Usually, compilations don’t do a serious amount of field study and this seems to have a very robust pilot data record.

Giant Reed is a robust perennial grass. It looks like bamboo, smells like bamboo, can be utilized like bamboo, but it is not bamboo. It has a nice network of rhizomes and root spread from around 5-30 cm in depth and over 100 cm long. These roots are tough and fibrous, making it a plant with some fortitude. The reed itself is thick and hard, just like a bamboo. This reed can survive in water-stressed areas, saline-contaminated soils, and provide excellent biomass in just a few weeks. It’s fast growing and doesn’t mind heavy metal contamination in its soil.

In fact, the authors of this study specifically looked at Giant Reed for the remediation of this nasty substance called red mud. Red mud is the byproduct of aluminum mining and refining. It’s a combination of bauxite, iron ore, caustic materials used to extract the aluminum, and typically has a fierce pH at about 14. They dump seawater on it to drop the pH and recover the caustic refining chemicals. Then industry dumps it in the ocean or a river and hopes that it doesn’t kill everything right away. Some companies are nice enough to dam it in huge slabs of muddy goodness that seems to work well enough until it a) leaches into surrounding soil and water systems or b) gets loose and goes on a field trip in a metal-contaminating, people crushing lahar of doom and destruction.

Because of giant reed’s fast growth, significant biomass, hyperaccumulation of metals and capability to grow in saline soil, this is one of the prime candidates for controlling the red mud scare. It’s like if communism made you take a chemical decontamination shower and destroyed your water system. Giant reed has a good translocation factor at 54.3 (though this was for a specific species of giant reed called Phragmites karka) with a strong preference for nickel (iron was less motivated at 8.51% uptake as opposed to 114.12% uptake. Its ability to grown in saline conditions is particularly useful since, as mentioned above, seawater is the dilution solution to the red mud issues. That excess salinity essentially salts the earth making most plant growth impossible without help. But giant reed doesn’t seem to mind.

A further advantage to giant reed seems to be in its ability to restore balance to the microbial community in these heavily disturbed soils. Microbes coexist with their soil ecosystems and require a certain population of organic predators, fungi, and roots to properly integrate into healthy soil. Giant reed is a clonal plant, meaning that it reproduces asexually and can’t be necessarily bred for specific effects using sexual selection. This does not preclude genetic engineering in controlled populations, however, and since the reed usually needs a growth period in non-contaminated soil to get its systems healthy enough to deal with contaminated areas, there exists a strong recommendation that the reed should be populated by greenhouse until a year or so prior to being planted in its remediation zone. This year of growth could also develop the soil with microbial and fungal populations unique to Arundo donax. Essentially, it would not just be a plant transplant, but also a microbial transplant with active mycorrhizal species safely cocooned in the soil with root systems for integration into the contaminated area when the population was strong enough.

A final benefit to this little plant is the fact that not many animals (including humans!) seem to like to eat it. Thus, the translocation of metals into its green bits would not pose a threat to animal or human life due to ‘grazers’ and its prodigious biomass production could be used for alternative energy sources or paper production. There are a number of industrial uses for this material including filters, biofuels, and feedstock for bioenergy. In conclusion, giant reed is a tough, fast-growing plant that shows very promising results for the remediation of many different kinds of metals in saline soils under a variety of environmental conditions, including water-stressed or water-limited areas, though its best growth is under wetland condition.