Species Differences in δ13C and δ18O in Arctic Shrubs: Evidence from a Snow Fence Experiment

Carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes provide key insights into plant physiological processes, including water-use efficiency, water source utilization, and carbon assimilation. In Arctic ecosystems, changes in snow conditions may influence shrub growth, physiology, and isotopic composition by altering soil moisture, temperature, and soil nutrient conditions with carry-over effects from winter to the main growing season. We analyzed δ¹³C and δ¹⁸O values in two dominant Arctic shrub species, Salix glauca (gray willow) and Betula nana (dwarf birch), growing at a snow fence experiment implemented summer 2012 on Disko Island, Greenland. Using novel laser ablation methods with beam sizes of 100μm and 40μm for δ¹⁸O and δ¹³C, respectively, we analyzed growth rings from 20 individuals per species, covering the period 2007-2017. In total, we obtained 255 δ¹⁸O measurements (122 for S. glauca and 133 for B. nana) and 352 δ¹³C measurements (175 for S. glauca and 177 for B. nana). We obtained annual resolution measurements of δ¹⁸O for 162 rings and of δ¹³C for 320 rings, despite narrow rings averaging ~93μm (~85μm for S. glauca and ~100μm for B. nana). Our preliminary results indicate that increased snow depth due to the snow fence did not significantly alter the carbon or oxygen values in either species. While δ¹⁸O values were similar between the species, suggesting similar water sources regardless of snow depth, S. glauca had significantly enriched δ¹³C values than B. nana, indicating greater water-use efficiency, which may give it a competitive advantage during drier periods. These findings suggest that species-specific physiological traits, rather than snow depth changes, may be the primary drivers of isotopic differences in Arctic shrubs, with implications for shrub expansion and Arctic carbon and water cycles.