This file contains the delta 15N values for leaf material collected from Cyathea rojasiana tree ferns before and after fertilization using ammonium -15N chloride solution to determine whether 15N update is possible from senescent leaves.

Details of the experiment are provided in the online supplement to the published paper. Briefly, In February 2022 we selected three mature C. rojasiana individuals 1-1.5m in height that had leaves rooted in the soil and one new developing (but unexpanded) leaf. For each fern, two plastic pots (10 x 10 x 12 cm) were filled with a 50:50 mixture of washed river sand and soil from the Chorro watershed. For each pot, one senescent leaf that was rooted in the soil was carefully excavated and its roots transplanted into the pot. Pots were then fertilized by adding 30 ml of a 0.02 M 15N solution of ammonium-15N chloride (98% 15N; Sigma-Aldrich 299251; St Louis, MO) to yield a target concentration of 2 µg15N cm-3 of soil. After fertilization pots were carefully enclosed within thick plastic bags, and sealed around the senescent leaf rachis to prevent leaching any of 15N from the pot to the surrounding soil.

At the time of N fertilization, pinnae of the youngest fully expanded leaf were collected from each fern. One pinna was collected from the base of the leaf and one from the distal end of the leaf. In March 2022, after 28 days the roots were removed from pots and two additional leaf pinnae sampled from each fern: one from the base and one from the distal end of the youngest (now fully expanded) leaf. Leaf samples were dried for 72 hours at 60 C and then leaf lamina tissue finely ground with a bead beater. The delta 15N for each leaf sample determined at the University of Illinois, Urbana-Champaign using a Thermo Delta V Advantage IRMS run in combination with a Costech 4010 Elemental Analyzer. Samples were run in continuous flow relative to laboratory standards that were calibrated with USGS 40, 41, and NBS 19 reference materials.