The δ¹⁵N of lettuce and barley are affected by AM status and external concentration of N

Abstract

Mean δ¹⁵N of whole-plants of lettuce and barley varied by [les ]3‰ when given a chemically and isotopically uniform N source. This variation was related to the presence, absence and species of arbuscular mycorrhizal (AM) fungi and to external N concentration. A highly AM-susceptible plant (lettuce) responded to treatments differently than a less susceptible one (barley). The largest change in whole plant δ¹⁵N was related to the experimental combination most likely to be found in field conditions: species of fungus interacting with varying external concentrations of N.

The mechanisms underlying observed variations of plant δ¹⁵N are not understood, nor can they be approached directly using δ¹⁵N. However, descriptive data, such as presented here, are important to the development of a mechanistic model, because they suggest relationships for future research, using inter alia¹⁵N-enriched tracers. They also confirm that plant N sources, cannot be identified using plant δ¹⁵N, even when the type of mycorrhizal association (endo vs. ecto) is known.