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This study explores how ant mounds affect nitrogen availability and plant productivity in the subarctic tundra, focusing on Betula nana, Vaccinium uliginosum, and Vaccinium vitis-idaea. Climate models show significant temperature increases in high latitudes, impacting tundra ecosystems through permafrost thawing and vegetation shifts. Ants, as ecosystem engineers, can change the soil through mound construction, potentially increasing nitrogen (N) availability, important for plant growth in nitrogen-limited tundra. Hypotheses suggest: A) lower C:N ratio near ant mounds, and B) more productive plants around mounds, using leaf area and number as proxies.

Fieldwork occured in Abisko, Sweden's tundra above the treeline. Shrub samples were collected at various distances from mounds, and leaf area and number were measured. Labwork involved preparing leaf samples for C:N analysis. One-way ANOVA tests were performed in RStudio to analyse differences in leaf amount, area, and C:N ratio.

Results showed B. nana had significantly lower C:N ratio at the mound top than 1m and 4m, supporting hypothesis A. B. nana had higher leaf area and number at the mound rim compared to 1m and 4m, supporting hypothesis B. V. uliginosum and V. vitis-idaea showed significant differences in mean leaf number between distances from mounds, but no significant leaf area differences. Ant mounds could positively impact nutrient availability and plant productivity, especially for B. nana, contributing to tundra greening. Understanding ants' influence in subarctic tundra will help us to predict the areas response to rising temperatures in the future.

Key words: artic tundra, plant productivity, ant mounds, nitrogen limitation, shrubs