Phytoremediation of microbial contamination in soil by New Zealand native plants

Novel research has demonstrated that the roots of some bioactive plants - called pathogen phytoremediation plants - enhance die-off of pathogenic organisms in the soil. Strategic establishment of pathogen phytoremediation plants may reduce the transport of human pathogens to water sources. Such plantings could be used in riparian margins, as buffer strips to protect drinking water supplies, or block planting in ‘critical source areas’ of microbial contamination, such as grazing paddocks, organic waste – including sewage sludge - amended land, animal feedlots and housing facilities, and manure storage areas. This work aimed to investigate the antimicrobial activity of a range of New Zealand native plants known for their antimicrobial potential from previous research or through indigenous knowledge, and to assess if any of them could potentially be used for pathogen phytoremediation. Two laboratory screening experiments demonstrated the antimicrobial activity of Leptospermum scoparium, including the local variety swamp mānuka, Kunzea ericoides, Pseudowintera colorata, and Metrosideros robusta against three human pathogens and two indicator organisms. A greenhouse experiment showed a 90% reduction of Escherichia coli numbers in dairy shed effluent irrigated pots after 14 days in soils under swamp L. scoparium and M. robusta, compared with 45 days in soil under Lolium perenne. The pH in the soil under swamp L. scoparium and M. robusta was significantly lower than under L. perenne, which could partially explain the faster E. coli reduction