Comparison of nitrogen uptake in the roots and rhizomes of Leymus chinensis

Leymus chinensis (Trin.) Tzvel is a rhizomatous grass species in the Eastern Eurasian steppe zone that is often limited by low soil nitrogen availability. Although a previous study showed that the rhizomes of L. chinensis have the capacity to take up nitrogen, the importance of such uptake for nitrogen nutrition is unclear. Moreover, little is known regarding the inorganic nitrogen uptake kinetics of roots and rhizomes in response to nitrogen status. Here, we first found that ammonium is preferred over nitrate and glycine for L. chinensis growth. Using the 15N-labelling method, we found that the rate of ion influx into roots was approximately five-fold higher than into rhizomes under the same nitrogen content, and the ion influxes into roots and rhizomes under 0.05 mM N were greater than in the presence of 3 mM N, especially in the form of NH4+. Using a non-invasive micro-test technique, we characterised the patterns of NH4+ and NO3– fluxes in the root mature zone, root tip, rhizome mature zone, and rhizome tip following incubation in the solution with different N compounds and different N concentrations. These results suggest a dynamic balance between the uptake, utilisation, and excretion of nitrogen in L. chinensis.