Variation in nitrogen‐use traits within and between five Carex species growing in the lowland mires of northern Japan

Abstract

Summary Theory suggests that there should be a trade‐off between nitrogen productivity (A) and mean residence time of nitrogen in plant tissues (MRT), and that this trade‐off depends on the N availability of the habitats. To test this, we studied A, MRT and nitrogen‐use efficiency (NUE, reciprocal of N concentration in the dead shoot) in wetland Carex species sampled from seven lowland mires in Japan. The NUE and MRT of unproductive species that usually grow in acidic and N‐poor habitats exceeded those of productive species that are abundant in weakly acidic and N‐rich habitats. Except for the most productive species, C. lyngbyei, interspecific differences in A were small, irrespective of productivity. Intraspecific variation in A was relatively large in contrast to those in NUE and MRT. Within each species, no parameter correlated with the concentration of total dissolved nitrogen (TDN) in the soil water. Although NUE and MRT of the plants growing in the weakly acidic habitats correlated negatively with TDN, they were constantly high in the acidic habitats regardless of the TDN concentration. Responses of A did not correlate with TDN concentration of soil water in either acidic or weakly acidic habitats. A trade‐off between A and MRT in the five Carex species was not detected in relation to habitat N richness. We suggest that soil water acidity dominates the ecological performance of the Carex species, and that the trade‐off between A and MRT does not necessarily apply to wetland vegetation.