Redistribution of the nitrogen reserves of15N-enriched stem cuttings and dinitrogen fixed by 90-day-old sugarcane plants

Sugarcane plants were grown in sandculture from¹⁵N stem cuttings approximately 3 cm long with one node (“nodes”) or 15 cm long, with two nodes (“seedpieces”), in nutrient solution without or with 8 mM of N. The decrease in the¹⁵N enrichment of plants growing in zero-N solution relative to the initial¹⁵N enrichment of the cuttings indicated N₂ fixation. The contribution from atmospheric dinitrogen to the total N of the plants amounted to 9.3% for those growing from nodes and 15.2% for those growing from seedpieces after 90 and 60-day growth periods, respectively. Most of the fixed nitrogen went to the root-N pool. From 9 to 39% of the N initially present in the stem cuttings was lost from the plants while about 45% of the remaining N was translocated to the shoots and roots during a 30-day growth period for seedpieces and a 15-day growth period for the nodes. More than 85% of the translocated N went to the shoots. At the end of a 60-day growth period (for nodes and seedpieces, respectively) about 35% of the initial N remained in the stem cuttings, irrespective of type of cutting or of the presence or absence of N in the nutrient solution.