Uptake of stable N isotopes by Myriophyllum spicatum is not selective

Preference for ¹⁴N over ¹⁵N was assessed for Myriophyllum spicatum L. by exposing shoots to the same initial concentration of N, but different isotopic compositions (100% ¹⁴N, 50% ¹⁴N and 50% ¹⁵N, and 100% ¹⁵N) 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) % ¹⁵N was twice as high in the 100% ¹⁵N treatment as in the 50% ¹⁵N treatment, and the at% of the ¹⁴N treatment (0% ¹⁵N) remained unchanged. This observed absence of preference for ¹⁴N in M. spicatum suggests that this species can be useful in determining N sources to freshwater systems, which often differ in ¹⁵N/¹⁴N ratio.