Collection Protocol o  Collected water, sediment, & L. minor samples from the shore at 57 sites (ponds, wetlands, lakes, flooded areas)

Experimental Protocol o  20 populations with three treatment groups each:

•  control: only growth media •  vehicle control: 300ppb solvent in growth media •  PAH+: 300ppb PAH mix in growth media

o  ~1 frond + 2.5mL treatment solution in each well o  5 replicates per treatment, n=300 o  Photos taken before & after 10 days in growth chamber analyzed for change in surface area as proxy for change in biomass

Duckweed Tolerance to PAH Contamination Across the GTA Emma Lash, Jason Laurich, Chelsea Rochman and Megan Frederickson

Department of Ecology and Evolutionary Biology, University of Toronto

References 1 Oanh N.T.K., Reutergardh L.B. & Dung N.T.1999. Emission of polycyclic aromatic hydrocarbons and particulate matter from domestic combustion of selected fuels. Environ Sci and Technol, 33(16), 2703-2709. 2 Ngabe B., Bidleman T.F. & Scott G.I. 2000. Polycyclic aromatic hydrocarbons in storm runoff from urban and coastal South Carolina. Sci Total Environ, 255(1-3), 1-9. 3 Grijalbo L., Becerril J.M., Barrutia O., Gutierrez-Manero J., & Lucas Garcia J.A. 2016. Lemna minor tolerance to metal-working fluid residues: implications for rhizoremediation. Plant Biology, 18(4), 695-702. 4 Qin Y., Druzhinina I.S., Pan X., & Yuan Z. 2016. Microbially mediated plant salt tolerance and microbiome-based solutions for saline agriculture. Biotechnology Advances, 34(7), 1245-1259 Fig 2. 24-well plate setup

Fig 1. Collection procedure

Materials: q  Krajncic

inorganic growth media

q  EPA 16 Priority PAH solution mix in CH2Cl2:MeOH (1:1)

Fig 3. Map of collection sites across the GTA. Sites used for experiment marked in green.

 

1.  Is there variation in the level of PAH contamination across bodies of water in the GTA? 2.  Is there variation between L. minor populations across the GTA in their ability to tolerate PAH contamination?  

o  Polycylic aromatic hydrocarbons (PAHs) are widespread environmental pollutants produced by the incomplete combustion of organic matter (e.g. coal, oil, wood) 1

››› Aquatic ecosystems become contaminated with PAHs through atmospheric deposition, surface runoff, petroleum spills, and industrial wastewater 2 o  The duckweed species Lemna minor is associated with a diverse microbiome that enhances plant growth and

performance 3 o  Plant microbiomes are highly variable, and beneficial microbes can increase their host’s ability to grow in

challenging environments 3,4 o  Thus, local adaptation to environmental pollution may exist in both host plant genomes and in their microbiomes o  We are investigating whether PAH contamination and duckweed resistance to PAHs vary across the GTA o  Once we know whether this variation exists, we will be able to explore whether host or symbiont genetic

mechanisms provide the basis for this variation o  We collected water samples and L. minor populations from across the GTA and assessed their growth responses

to the presence of 16 priority PAHs o  With these data, we will be able to assess how the presence of pollutants affects plant microbiome composition

and whether these beneficial microbes play an important role in helping plants tolerate and degrade environmental contaminants

o  Duckweeds often grew more in the PAH and vehicle treatments than in the control, suggesting that plants took up DOC from the solvent

o  Significant interaction effect between site and treatment indicates that populations differ in their response to solvent/PAHs

o  In some populations, PAHs increased growth rate or had no significant effect on growth rate ››› Indicates some populations may have an adaptive mechanism that enables them to survive in polluted environments o  Is it a host or symbiont genetic mechanism that is driving the variation in contaminant

tolerance among populations? ››› Future: Experiment with presence/absence of the microbiome to determine if it is host genotype or microbiome composition that is driving this variation o  Quantify the amount of PAH contamination at each site and ask: ››› Is there a correlation between the amount of contamination in a population’s native environment and its ability to tolerate and breakdown PAHs in the lab? ››› Are certain microbiomes often associated with certain types or levels of contaminants?

Introduction  

Research Questions  Methods

Fig 5. Final biomass of L. minor from 20 different source populations exposed to three treatments. Treatment had a significant effect on host growth rate, and there was a significant treatment by site interaction. (p<0.001)

Fig 4. Threshold quantification of final biomass of duckweed in well plate.

Acknowledgements Thank you to everyone in Frederickson lab for welcoming me so graciously into your lab this summer. A special thank you to Jason, Chelsea and Megan for your guidance, encouragement and feedback over the course of this project. Funding provided by the Centre for Global Change Science.

300  ppb    

Results  

Discussion and Future Directions