Uptake of stable N isotopes by Myriophyllum spicatum is not selective

Abstract

Preference for 14 N over 15 N was assessed for Myriophyllum spicatum L. by exposing shoots to the same initial concentration of N, but different isotopic compositions (100% 14 N, 50% 14 N and 50% 15 N, and 100% 15 N) for 6 weeks. Regardless of treatment, all available inorganic N was taken up by M. spicatum at similar rates. Significant differences in tissue isotopic composition were evident across treatments in 2 weeks, and persisted for the remainder of the experiment. At 6 weeks, atom (at) % 15 N was twice as high in the 100% 15 N treatment as in the 50% 15 N treatment, and the at% of the 14 N treatment (0% 15 N) remained unchanged. This observed absence of preference for 14 N in M. spicatum suggests that this species can be useful in determining N sources to freshwater systems, which often differ in 15 N/ 14 N ratio.