Data from: Long-term heavy reindeer grazing promotes plant phosphorus limitation in arctic tundra

1. The potential of large mammalian herbivores to shift plant communities between nitrogen (N) and phosphorus (P) limitation has received little attention so far. However, herbivores can influence the cycling of these growth-limiting nutrients, and thereby affect plant nutrient limitation and productivity. Tundra ecosystems are nutrient-poor and commonly grazed by large herbivores like reindeer and may thus be responsive to such changes. 2. Here we examined the effect of long-term light and heavy reindeer grazing on nutrient limitation of plant growth in a Scandinavian arctic tundra. We are the first to conduct a factorial N and P fertilization experiment across the two grazing regimes in two functionally contrasting vegetation types: heath and meadow. 3. Annual primary productivity (APP) showed contrasting responses to our fertilization treatments under light and heavy grazing. Under light grazing, APP increased in response to N + P additions in both the heath and meadow. Under heavy grazing, APP increased in response to N in the heath, with an additional positive effect of N + P combined, while APP increased in response to P and N + P additions in the meadow. 4. These results clearly show that an increase in the grazing intensity of reindeer facilitated a shift towards more P limited conditions in Scandinavian arctic tundra, by increasing N cycling without having a corresponding positive effect on P cycling. In the N-poor heath, reindeer increased soil N availability at least partly due to a shift towards more N-rich graminoids, while in the meadow reindeer decreased soil P availability. The mechanisms behind this decrease remain unclear, but reindeer may simply export more P from the system than N due to their large P demand for the production of their antlers. 5. Synthesis. We conclude that heavy and long-term reindeer grazing promoted a more P limited tundra, thus experimentally confirming the potential of large mammalian herbivores to influence nutrient limitation of plant growth.Annual Primary Productivity data from NP fertilization experimentThe datafile contains 2 sheets, the first sheet contains the metadata and the second sheet contains the actual data. The data are from a full-factorial nitrogen (N) and phosphorus (P) addition experiment performed in the artic tundra in two contrasting vegetation types (heath and meadow) under two contrasting reindeer grazing regimes (lightly and heavily grazed). We collected data on annual primary productivity (in g per m2) of 4 different plant functional types (deciduous shrubs, evergreen shrubs, forbs, graminoids).Fertilization experiment_APP.xlsxR script used for the statistical analysesThis document contains the R script used for the statistical analyses of the paper: 'Long-term heavy reindeer grazing promotes plant phosphorus limitation in arctic tundra' by Sitters et al.Rscript_Fertilization experiment_Sitters.doc