In controlled N-nutrition experiments, differences in delta15N composition of leaves and roots are regularly found. In this paper we report results from a survey of nitrogen stable isotope signatures of leaves and roots of 16 plant species growing under natural conditions in a meadow and a forest understorey, which differed in nitrate and ammonium availability. Significant differences between leaf and root were observed. The range of delta15N [leaf-root] values was -0.97 to +0.86 per thousand, small compared to published values from controlled N-nutrition experiment, but almost as large as the range of leaf delta15N values (-1.04 to +1.08 per thousand). Forbs showed the largest differences between leaves and roots and showed a significant difference with respect to habitat. Grasses and legumes did not show significant differences in delta15N [leaf-root] between the two habitats. Care must be taken when using leaf delta15N values as representative for whole-plant 15N composition in these two habitats.