Nutrient effects on autofragmentation of Myriophyllum spicatum

Abstract The effects sediment nitrogen and water potassium concentrations have on autofragment production of Eurasian watermilfoil ( Myriophyllum spicatum L.) were studied utilizing 16 mesocosms with four mesocosms per treatment. Results indicated that a sediment nitrogen concentration of 0.04 mg NH 3 -N g −1 sediment significantly increased autofragment production. Plants grown for 12 weeks in this low nitrogen regime produced 1616 autofragments while high nitrogen treated plants (0.55 mg NH 3 -N g −1 sediment) produced 712 autofragments. Potassium concentration did not significantly alter autofragment production. Up to 50% of autofragments abscised from parent plants grown under low nitrogen conditions compared to 12% or less when grown under high nitrogen conditions. Within 10 days of initiating adventitious roots, 16–38% of autofragments broke away from parent plants grown under low nitrogen regimes compared to 10% of autofragments grown under high nitrogen regimes. Plant components (inflorescence, autofragment, stem and root crown) contained equivalent percentages of total nonstructural carbohydrates (TNCs) by the 9th week of growth; however, low nitrogen treated plants were producing more autofragment and stem biomass. The combination of these factors indicates that Eurasian watermilfoil grown in a low nitrogen environment directs more resources toward autofragment and stem production, allowing colonization of new potential sites. In contrast, when grown in a high nitrogen environment, this species directs more of its energy toward stem and root crown development, allowing for regrowth and colonization in the immediate area.