Tracing fresh assimilates through Larix decidua exposed to elevated CO2 and soil warming at the alpine treeline using compound‐specific stable isotope analysis

摘要: Summary How will carbon source–sink relations of 35-yr-old larch trees (Larix decidua) at the alpine treeline respond to changes in atmospheric CO2 and climate? We evaluated effects previously elevated concentrations (9 yr, 580 ppm, ended previous season) ongoing soil warming (4 yr, + 4°C). Larch branches were pulse labeled (50 at% 13CO2) July 2010 trace fresh assimilates through tissues (buds, needles, bark wood) non-structural compounds (NCC; starch, lipids, individual sugars) using compound-specific isotope analysis. Nine years did not lead increased NCC concentrations, nor increase transfer velocities. By contrast, we found slower velocities higher than reported literature for lowland larch. As a result low dilution with older carbon, sucrose glucose showed highest maximum 13C labels, whereas labels lower lipids pinitol. Label residence times needles shorter starch (c. 2 d) 6 d). Although our treatments no persistent effect on relations, temperature high altitudes clearly induced limitation sink activities (growth, respiration, root exudation), expressed concentrations.