Proposed explanations for these contradictory results include the importance of other factors than initial nutrient availability in determining the net effect of herbivores on soil N, such as trampling-induced soil compaction or lateral transport of nutrients between habitats (Sitters and Olde Venterink ).
In addition, a recent model analysis predicts that herbivory will decrease microbial activity by reducing C supply to the soil through consumption of plant biomass and will thus have a negative effect on N availability at low plant C/N ratios through a decrease in mineralization rates and a positive effect at higher plant C/N ratios through a decrease in immobilization rates (Cherif and Loreau ).
The aim of this study is therefore to determine the long-term effects of reindeer on soil N and P availabilities and plant nutrient traits across a topographic gradient encompassing both nutrient-poor and nutrient-rich environments.
More specifically, we test the hypotheses that herbivory will have a negative effect on N and P availabilities in nutrient-rich environments and a positive effect in nutrient-poor environments.
Mean annual temperature at the site was −3.3°C based on local loggers, and the average precipitation at the nearest climatic station (Kautokeino) is 389 mm/year.
We conducted the study across a reindeer fence, established in the 1960s to prevent reindeer from entering their winter ranges during summer.
We want to emphasize that grazing in this study includes trampling on the vegetation in its definition.
for a description of topographic gradients in the arctic).
We determined long-term effects of reindeer on soil extractable nitrogen (N) and phosphorus (P) and their net mineralization rates along a fertility gradient of plant carbon (C) to N and P ratios in arctic tundra.
Our results showed that reindeer had a positive effect on soil N in the more nutrient-poor sites and a negative effect on soil P in the more nutrient-rich sites, which contrasts from the general consensus.