Long‐term effects of nutrient enrichment controlling plant species and functional composition in a boreal rich fen

Abstract

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.

Plant distribution, stature, rarity, and diversity in a patterned calcareous fen: tests of geochemical and leaf‐height models

“…Indeed, Øien et al. () recently found strong evidence for co‐limitation of fen production by P and N in a 15 yr study involving factorial application of N, P, and K.…”

“…() found P limitation in microsites with low standing crops, and N limitation in microsites with high standing crops. P limitation has subsequently been demonstrated in several calcareous spring fens via fertilization experiments or inferred from NPK stoichiometry of live leaf tissue (e.g., Koerselman and Meuleman, ; Bedford et al., ; Olde Venterink et al., ; Rozbrojová and Hájek, ), but some fens appear to be jointly limited by N and P (Cusell et al., ; Øien et al., ), and sulfide production plays a key role in reducing coverage by dominant plants near springheads in one New York fen (Simkin et al., ).…”

Changes in functional, phylogenetic and taxonomic diversities of lowland fens under different vegetation and disturbance levels

“…3 Mean SES values of functional (a = 0) and phylogenetic (a = 1) diversities of plant communities generated by UPGMA clustering. Error bars denote 95% confidence intervals probably being driven by differences in environmental variables between the two communities influenced by localised nutrient enrichment, soil chemistry, water table height and peat depth (Øien et al 2018;Pillar et al 2009).…”

Cryptogams and dwarf evergreen shrubs are vulnerable to nitrogen addition in a boreal permafrost peatland of Northeast China

“…These observations suggest that, due to the interspecific variations of eco‐physiological strategies, the biomass responses to N enrichment are divergent among plant growth forms in boreal peatlands. Similar to N, P is also an important nutrient for plant growth in peatlands (Øien, 2004; Li et al, 2019; Salmon et al, 2021), especially in rich fens (Øien & Moen, 2001; Øien et al, 2018), given that N enrichment often aggravates P limitation of plant production by disturbing the stoichiometric balance between N and P (Li et al, 2016). In this peatland, elevating soil N:P ratio after N addition (Appendix S2) indicates the N:P stoichiometric imbalance, implying that P availability may determine the ultimate response of plant biomass to N enrichment.…”

“…Because N is considered a major limiting nutrient for plant growth in many terrestrial and aquatic ecosystems (Du et al, 2020), continually increasing N availability can impact plant composition and productivity (e.g., Payne et al, 2017; Li et al, 2019; Midolo et al, 2019; Ma et al, 2020). However, plant responses to N enrichment are highly dependent upon plant growth form, N addition level, and experimental duration (Yang et al, 2011; Scarpitta et al, 2017; Øien et al, 2018; Levy et al, 2019; Lin et al, 2020). Thus, the responses of plant communities to ongoing N enrichment are unclear, particularly in nutrient‐poor ecosystems.…”