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Questions: How does long‐term increase in nutrient availability affect species composition, species diversity and functional composition in boreal rich fens, and how does this differ from short‐term effects? What are the possible mechanisms behind the observed changes, and how does nutrient limitation influence species diversity in these communities? Location: Sølendet Nature Reserve, central Norway. Methods: A full‐factorial field experiment. Plots in two localities received one of following treatments (n = 3): no nutrient addition (control), N, P, K, NP, NK, PK and NPK addition. Cover of plant species was recorded before treatment, and after two and 15 years of treatment. Results: Two years of nutrient addition caused small changes in species composition, but addition of NP led to large increase in abundance of species with high ability to exploit the added nutrients—a direct result of the elimination of nutrient limitation in the communities. After 15 years of nutrient addition there were significant changes following three different pathways, one for each of N, P and NP addition. The addition of NP led to large community shifts, considerable species turnover and reduced species and functional richness, mainly caused by increase in cover of highly competitive and tussock‐forming grasses like Deschampsia cespitosa, Festuca ovina and Molinia caerulea, out‐competing other species, especially bryophytes. Addition of N led to smaller changes in species turnover, and without clear dominant species. Addition of P led to considerable species turnover, but no reduction in species or functional richness, and the bryophyte diversity increased. This is explained by the bryophytes' association with N‐fixing cyanobacteria, suggesting less N limitation and a greater ability to utilize the added P when vascular plants suffer from N shortage. In addition, bryophytes are more sensitive to low P availability, due to larger P requirements compared to vascular plants. There was no effect of K addition. Conclusions: Both N and P limitation is essential for the maintenance of high species diversity in boreal rich fens, and P limitation controls bryophyte diversity. From a management perspective, N and P limitation is vital in the conservation of boreal rich fens or when a functional fen system is reestablished through restoration measures. Long‐term addition of N and P in a boreal rich fen caused changes in species composition following three different pathways. Addition of NP: reduced species and functional richness. Highly competitive grasses out‐competed other species, especially bryophytes. Addition of P: large species turnover, but no reduction in species or functional richness; bryophyte diversity increased. Addition of N: only smaller changes without clear dominants. [ABSTRACT FROM AUTHOR]

Question How does pioneer vegetation of acid inland dunes respond to addition of nitrogen (N) and phosphorus (P)? Location Two inland dune reserves in The Netherlands with low and high N deposition. Methods During 2.5 yr, N and P addition (control, N, P, NP) took place in three different vegetation types of inland dunes ( Polytrichum piliferum mats, Campylopus introflexus mats and lichen-dominated vegetation). In each site, changes in the vegetation were recorded in three replicate quadrats of 1 m × 1 m per treatment. Differences in element content of grasses and lichens were recorded, together with vegetation parameters, including cover and height of grasses, bryophytes and lichens. Results In the site with high N deposition, grasses were taller, had higher N:P ratios and a generally lower lichen cover than in the low-deposition area. Experimental N application resulted in higher N and lower base metal concentrations in grasses and an increase in grass cover and size. In contrast, lichens showed a general decline in the N treatment and the lichen:grass ratio decreased. The effect of N addition was larger in the low-deposition area. The P treatment had an opposite effect: lichens increased in size and cover and overgrew grasses, especially when reindeer lichens were present. This suggests that the cryptogam layer was P-limited even in the low N deposition site. Conclusions Pioneer vegetation in inland dunes is susceptible to N and P addition. The results provide evidence for a decrease in lichen cover due to increased N deposition. [ABSTRACT FROM AUTHOR]