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 N-15 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 N-15 transported toward the apical part was markedly reduced at the higher external N level, whereas the amount of N-15 transported toward the basal part was unrelated to the external N levels. The rate of N-15 acropetal transport basically averaged 20.9%, and the rate of N-15 basipetal transport generally ranged between 0.2% and 6.3%, both being negatively dependent of Delta PNC (i.e., difference in plant N concentration [PNC] between apical and basal parts). The proportion of N-15 in stems and leaves averaged 74.7% and 18.1%, respectively; the proportion of root N-15 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.

Automated summary

Quantitative tests were conducted to measure the transport rate and partitioning pattern of nitrogen (N) in a clonal species Alternanthera philoxeroides. The results showed that the transport of N towards the apical part was reduced at higher external N levels, while the transport towards the basal part was unaffected by external N levels. The rate of N transport to the apical part averaged 20.9%, and the rate of N transport to the basal part ranged between 0.2% and 6.3%, both dependent on the difference in N concentration between the apical and basal parts.