Fragment viability and rootlet formation in Eurasian watermilfoil after desiccation

Journal of Aquatic Plant Management, 49: 57-92

Celia Evans, Daniel Kelting, K.M. Forest, & L.E. Steblen

Eurasian watermilfoil often invades aquatic ecosystems in North America via fragment transport from infested lakes to uninfested water bodies by watercraft and boat trailers. While fragments transported on watercraft and trailers are likely introduced to new water bodies in various stages of desiccation, surprisingly little is known about the desiccation tolerance and subsequent viability of Eurasian watermilfoil. We conducted in situ and laboratory experiments during the 2010 growing season to examine (1) the rate at which Eurasian watermilfoil desiccates, (2) the likelihood of new growth and rootlet formation in control fragments and fragments that had been desiccated for 3, 6, 18, 24, and 48 h, and (3) time until new growth and rootlet formation in the different treatment groups. We found that desiccation over time fits a Michaelis-Menten type function on which 87% and 96% desiccation occurred after just 3 and 6 h, respectively, and 100% desiccation of milfoil fragments occurred at approximately 13 h under laboratory conditions. Based on a logistic regression model, desiccation significantly reduced the likelihood of fragment viability from 98% in control fragments to 2% in fragments that were completely (100%) desiccated in the laboratory experiment. Desiccation also increased the time until new growth and rootlet formation. In control treatments, 20% of Eurasian watermilfoil nodes produced new growth (via lateral bud growth) after 5 weeks, and 90% of those produced rootlets. Although desiccation significantly reduced Eurasian watermilfoil fragment viability, a small proportion (2%) of fragments that were 100% dried were still viable and able to form rootlets.