Greater nitrogen and/or phosphorus availability increase plant species’ cover and diversity at a High Arctic polar semidesert

Enhanced nitrogen (N) deposition at high latitudes is a circumpolar phenomenon. Low soil phosphorus (P), however, may limit vegetation responses to increased N inputs. From 2000 to 2002, the effects of N at 0, 0.5 (a rate occurring in Greenland and Iceland) and 5 (equivalent to deposition in areas of Europe) g N m⁻² a⁻¹ and P (0.1 g m⁻² a⁻¹) treatments on plant species’ cover and diversity were determined at a polar semidesert site (ambient deposition c 0.1 g N m⁻² a⁻¹) in Svalbard (79°N). The largest response was to combined 5 g N plus 1 g P m⁻² a⁻¹, where cover of Saxifraga oppositifolia increased c fourfold, density of Salix polaris leaves c ninefold, seedlings of several ‘new’ species (Draba oxycarpa, Saxifraga caespitosa, Sagina nivalis) were established and ‘immigration’ of Bryum arcticum and ‘extinction’ of Schistidium apocarpum were observed. There were fewer, less pronounced, effects on the plant community at 0.5 g N m⁻² a⁻¹. Low P availability did indeed appear to restrict vegetation response to N. There was a trend for plant species’ richness and diversity to increase with 1 g P m⁻² a⁻¹ at 0 and 0.5 g N m⁻² a⁻¹, but not at 5 g N m⁻². Plant species showed individualistic responses so that generalisation by functional type was not possible. Such increased colonisation by moss species of bare soil, and greater densities of previously unrecorded angiosperm seedlings, are not usually observed in more closed (subarctic) tundra as a response to N and P additions. These changes are likely to influence significantly nutrient cycles, whole system carbon budgets and surface energy and water balances. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.