Heavy metal contaminants are capable of movement through the environment and having deleterious effects on members of local ecosystems. Additionally, heavy metals persist indefinitely in an ecosystem unless physically removed. Therefore developing methods for efficient removal of heavy metals from the soil is paramount. Phyotextraction is a low-cost green technology that utilizes heavy metal hyper-accumulators (HMHs) to remove heavy metals from the soil. HMHs are plants capable of extracting heavy metals from contaminated soil by accumulating the heavy metals in their aerial tissues. However, despite the unique abilities of HMHs and the growing interest in phytoextraction, the technology is not yet efficient enough to be considered economically viable.
Microbes in the rhizosphere are known to be important for plant growth and are one avenue to improve phytoextraction of HMHs. Currently little is known regarding the interaction between rhizosphere associated microbes and HMHs in heavy metal contaminated soils. This work reports on factors that are important for plant-microbe interactions in the presence of heavy metal contaminated soils. By investigating which factors direct the formation of rhizosphere communities on contaminated soil and by identifying microbial process with the greatest impact on metal accumulation, such as plant-hormone production, plant stress inhibition and the solubilization of key nutrients, we propose to begin utilizing non-HMHs for phytoextraction. These results suggest that heavy metal contamination is the predominant driver of rhizosphere community formation. Potentially, heavy metal resistant microbes that encourage plant growth and heavy metal accumulation could be used to increase the range of plants for phytoextraction.
Although counterintuitive, the ability to use any plant in phytoextraction will circumvent the low biomass, harvestability and biosecurity problems associated with HMHs. With the assistance of the correct microbial community, easily harvestable high-biomass crop species could improve phytoextraction efficiency, even if they have no native hyper-accumulation ability