Non-native Phragmites (common reed) plants continue to invade wetlands and other sensitive ecosystems across the nation, causing degradation of fish and wildlife habitat, reduced recreational opportunities for the public, and altered water movement patterns. Reducing the impacts of this plant is a high priority for resource managers, but the existing approaches to manage the plant (e.g., herbicide, cutting, flooding, burning) are resource intensive, often kill native plants, and can have other undesirable effects. New management approaches that target the microbiome are being developed since, like many other plants, the non-native Phragmites forms symbiotic relationships with bacteria, fungi, and other microbes that influence nutrient acquisition, increase stress tolerance, and confer a suite of other benefits. These approaches will complement other developing control strategies (e.g., insect biocontrol, genetic biocontrol) and offer resource managers more treatment options.
Our development of microbe-based treatments for the non-native Phragmites began when a group of scientists from several research agencies began working together as the Phragmites Symbiosis Collaborative. This Collaborative published a research agenda in 2015 (http://doi.org/10.3389/fmicb.2015.00095) to provide a framework to advance our understanding of plant-microbe relationships and support invasive species management. Since the research agenda was published, several federal and academic institutions that participated in the Collaborative completed studies that shed light on the composition of microbes in and under invasive Phragmites clones, the pathogenicity of endophytes in Phragmites leaves, how soil bacteria enhance nutrient acquisition, and how microbial communities differ between native and non-native Phragmites plants.
The research agenda published in 2015 guided subsequent research efforts and resulted in significant advances in our understanding of the Phragmites microbiome that lay the foundation for the development of new microbe-based control treatments. There is a high fungal diversity associated with Phragmites, with more found in the rhizomes than in the leaf tissues. Several of the endophytes found in Phragmites are pathogenic, but the majority are non-pathogenic. Soil nutrients and stand density influence the soil microbiome associated with Phragmites and the differentiation between the native and non-native lineages. The rhizophagy cycle plays a role in how the non-native Phragmites acquires nutrients and offers a potential target for new treatments. Treating Phragmites with organic salts and sugars appears to interfere with nutrient acquisition and thus inhibit root and shoot development. These and other antimicrobial compounds offer new opportunities to develop Phragmites treatments that disrupt plant-microbial relationships and reduce plant vigor.