Fate of recently assimilated carbon in the soil–plant system of Vaccinium vitis-idaea and its response to warming in a 2.5-year translocation experiment

Abstract Background and aims Shrubs like Vaccinium vitis-idaea substantially contribute to forest carbon (C) sequestration. Therefore, understanding their allocation patterns under climate change is crucial. We conducted a translocation experiment with 13 CO 2 pulse-labelling to test if (I) belowground pools accumulate total and recently assimilated C, (II) within fine roots, assimilated C is preferentially allocated to root tips and mycorrhized cells and (III), whether warming alters C allocation patterns. Methods We translocated soil cores with V. vitis-idaea from North- to South-Finland (+ 3.7 °C mean temperature). After 2.5 years, we excavated and pulse-labelled them with 13 CO 2 , tracing the 13 C in plant, soil, and respiration. We used laser-ablation isotope ratio mass spectrometry to examine 13 C distribution in fine roots. Results Roots represented the largest plant C pool (north: 49.69 ± 9.73%, translocated: 43.92 ± 6.59% of plant C stock). A substantial amount of recently assimilated 13 C was recovered belowground (roots + soil, north: 15.59 ± 5.77%, translocated: 39.21 ± 29.32%) 8 days after labelling. Most assimilated C was respired (north: 63.3 ± 5.9%, translocated: 44.1 ± 3.2%) or recovered in leaves (north: 17.9 ± 5.92%, translocated: 19.2 ± 3.19%). Within fine roots, 13 C content tended to be higher at root tips, while mycorrhizal infection had no effect. Warming tended to increase C allocation to the shoot and significantly decreased 13 C in the microbial biomass in the mineral soil. Conclusion V. vitis-idaea allocates a large portion of assimilates belowground, but 2.5 years of warming only marginally change C allocation patterns. Accelerated soil microbial processes after translocation may increase plant N availability, potentially affecting C allocation over longer time spans.