The goal of the project is to support wastewater treatment facilities’ transition away from invasive Phragmites by systematically seeking native Phragmites strains with high dewatering ability.
An obstacle to statewide control of invasive Phragmites australis (common reed) in Minnesota is its continued use for dewatering biosolids in wastewater treatment facilities, a “green technology” leveraging invasive Phragmites’ exceptional ability to take up water and transpire it to the atmosphere. Development of an alternative to invasive Phragmites is essential for eliminating wastewater treatment facility source populations that can drive reinvasion in Minnesota despite efforts to control it across the landscape. Native Phragmites (P. australis ssp. australis) is an obvious alternative, but its use in wastewater treatment facilities to date has produced mixed results.
- Select native Phragmites source populations and controls for testing
- Experimentally evaluate performance of native Phragmites
- Disseminate results to wastewater treatment facility operators and other stakeholders
Native Phragmites ideally suited for dewatering would exhibit a suite of traits that enable it to remove water at high rates. The project includes a series of measures and experiments spanning from the field to the lab to identify native Phragmites that has these qualities. Rather than attempting to define a precise benchmark (e.g., “native Phragmites must remove 80% as much water as invasive Phragmites”) as wastewater treatment facilities’ needs vary with their engineering, storage capacity, and the needs of the communities they serve, the project will instead estimate how close we can get to the benchmark of invasive Phragmites and provide this information to wastewater treatment facility operators and engineers to guide their transition planning. The study will begin by characterizing a relatively large number of candidate native genotypes and then select promising ones for further investigation of water removal at different growth stages. If successful, this research would benefit AIS control in Minnesota by advancing toward a safe alternative to invasive Phragmites in wastewater treatment facilities.
In 2021, researchers harvested plant material for propagation from 10 populations of Phragmites australis. Rhizomes from eight populations of native and one population of invasive Phragmites were harvested for the project. The native populations were selected from 47 populations that were genotyped during Subproject 32 (Developing a genomic method to detect hybridization between native and invasive Phragmites australis). The native populations were chosen from geographically dispersed locales around Minnesota, and include populations that we categorized as especially robust, others that represent more typical growth (stature, density) of native Phragmites, and one population that can be described as having a weak growth habit. Because evidence of hybridization was documented in Minnesota Phragmites populations during the genotyping study, and some of the hybrids have a native phenotype, it was important to determine the nativity of populations that will be candidates for wastewater treatment alternatives. It is hoped that use of local genotypes will reduce potential negative impacts to the environment from spread of invasive populations or introduction of native populations from other states that might not be as well-adapted to Minnesota’s climate and environment. In addition, comparing water removal capacity across disparate populations collected throughout Minnesota will broaden our portfolio of plant materials to identify high-functioning genotype for use in wastewater treatment facilities.
A literature review was conducted in the initial phase of the project, with researchers using published literature to establish protocols for multiplying the clonal material required for the forthcoming water removal experiments. Containers and growth media for establishing the rhizomes and for growing out the plants have been set up in the Plant Growth Facility at the University of Minnesota, where the populations from around the state will be grown in a common garden experiment. Sensors for monitoring the growth environment are being set up and calibrated.
In late 2021, researchers succeeded in propagating the plant material for the 10 experimental populations of Phragmites australis. This work provided some insights into the opportunities and challenges of scaling up propagation for installing native Phragmites in reed beds. Although rhizomes are typically used by practitioners to establish reed beds, stem cuttings were more effective for generating clones for this research. Six of the native populations could be established; the others did not establish well enough to be used. Replicates for seven populations (six native populations plus one invasive control) were grown in a common garden, i.e., all populations were grown under the same conditions in a growth chamber to isolate population-level, genetic differences from potentially confounding environmental differences across the locations they were collected from. After several months of growth under these controlled conditions, we measured plants’ physical traits, including plant height, shoot number, total leaf area, and biomass and evaluated their water-removal capacity using gas exchange and stomatal conductance measures. Each of these parameters relate to the ability of the plants to transpire water, and thus function well for biosolids dewatering. The capacity of the native Phragmites populations to transpire water will be compared to that of the invasive population. These data have not yet been analyzed. An additional test of water removal capacity, lysimetric water removal, will then be conducted on the high-performing populations. These measures are scheduled for summer 2022.