Sharing of nitrogen between connected ramets of Alternanthera philoxeroides in homogeneous environments

Purpose Benefits of clonal integration have been widely documented in clonal species, but quantitative tests of the translocation of resources in both directions between older and younger ramets (e.g., transport rate and partitioning pattern) are still scarce. Methods A control experiment, using a clonal species Alternanthera philoxeroides as plant material and the technique of 15 N isotope, was conducted to quantify the transport rate of nitrogen (N) in two opposite directions (i.e., from younger to older ramets or the other way around) within a clone, and the partitioning proportion of N in recipient ramets. Results The amount of 15 N transported toward the apical part was markedly reduced at the higher external N level, whereas the amount of 15 N transported toward the basal part was unrelated to the external N levels. The rate of 15 N acropetal transport basically averaged 20.9%, and the rate of 15 N basipetal transport generally ranged between 0.2% and 6.3%, both being negatively dependent of ΔPNC (i.e., difference in plant N concentration [PNC] between apical and basal parts). The proportion of 15 N in stems and leaves averaged 74.7% and 18.1%, respectively; the proportion of root 15 N in the apical part significantly decreased from 7.6% to 0.4% when acropetal transport occurred. Conclusion These results suggest that N sharing between connected ramets tended to be acropetal and the partitioning pattern of N is organ-specific in A. philoxeroides , which potentially contributes to the early development of young ramets, and also to the spread of A. philoxeroides in limited N conditions.