Growth and functioning of Sphagnum mosses are closely linked to water level and chemistry. Sphagnum mosses occur in wet, generally acidic conditions, and when buffered, alkaline water is known to negatively impact Sphagnum. The effects of time, dose and species-specific responses of buffered, alkaline water on Sphagnum are largely unknown.• We investigated the effects of bicarbonate and calcium on the survival, growth and physiological functioning of seven Sphagnum species occurring in contrasting environments, from raised bogs to (rich) fens. Mosses were submerged in different concentrations of bicarbonate and calcium solutions for 10 weeks under climate-controlled circumstances.• After 2 weeks, all species exposed to the high bicarbonate treatment (2.0 mM) showed severe potassium leakage and swift discoloration. In contrast, species showed differential responses to the intermediate bicarbonate treatment (0.8 mM), some with a later onset of potassium leakage. S. squarrosum, S. teres & S. contortum generally persisted the longest, with all species dying after 6 to 10 weeks. Calcium alone, in contrast, negatively affected S. squarrosum, S. teres & S. contortum, causing discoloration and potassium leakage.• Our study shows enrichment with bicarbonate, but not calcium, is detrimental for most Sphagnum species tested. A mechanistic model was developed that is consistent with dose and duration dependence and the species specificity. Future conservation and restoration measures for Sphagnum-dominated habitats and Sphagnum farming (cultivation, production and harvest of Sphagnum moss biomass) should limit flooding with bicarbonate-rich waters while investigating new management options, like acidifying surface waters to lower bicarbonate levels.

Seagrass meadows form essential ecological components in coastal zones but are rapidly declining worldwide due to anthropogenic impacts, including eutrophication and climate change-related heat waves. An important consequence of increased eutrophication is organic matter input in the sediment, which, together with raised temperatures, stimulates the production of toxic sulfide. Although multiple recent studies have highlighted that seagrass can engage in a mutualistic relationship with lucinid bivalves alleviating sulfide toxicity in the rhizosphere, it remains unclear how this mutualism is affected by temperature and eutrophication. To unravel this relation, we investigated the response of the seagrass Zostera noltii to contrasting sediment organic matter conditions, temperatures and presence/absence of the lucinid clam Loripes orbiculatus in a full-factorial mesocosm experiment. Results demonstrate that temperature increased porewater sulfide and nutrient levels, particularly in treatments with high sediment organic matter content. Interestingly, L. orbiculatus reduced not only sulfide levels, but also porewater nutrients. The removal of sulfide in turn stimulated Z. noltii growth, despite lower nutrient availability. Finally, increased temperature suppressed the mutualistic benefit for Z. noltii as sulfide detoxification became hampered. We conclude that, as eutrophication remains an issue in the coastal zone and temperature extremes will likely become more common in the future, seagrass meadows where lucinids occur may need to increasingly rely on this mutualism. At the same time, however, this interaction will become more strained, with an inherent increasing risk of mutualism breakdown.

Aim The formation of a local vegetation mosaic may be attributed to local variation in abiotic environmental conditions. Recent research, however, indicates that self‐facilitating organisms and negative species interactions may be a driving factor. In this study, we explore whether heterogeneous geohydrological conditions or vegetation feedbacks and interactions could be responsible for a vegetation mosaic of rich and poor fen species. Location Lake Aturtaun, Roundstone Bog, Ireland. Methods In a floating fen, transects were set out to analyze the relation between vegetation type and rock–peat distance and porewater electrical conductivity. Furthermore, three distinct vegetation types were studied: rich fen, poor fen and patches of poor fen within rich fen vegetation. Biogeochemical measurements were conducted in a vertical profile to distinguish abiotic conditions of distinct vegetation types. Results Geohydrological conditions may drive the distribution of poor and rich fen species at a larger scale in the floating fen, due to the supply of minerotrophic groundwater. Interestingly, both rich and poor fen vegetation occurred in a mosaic, when electrical conductivity values at 50 cm depth were between 300 µS/cm and 450 µS/cm. Although environmental conditions were homogeneous at 50 cm, they differed markedly between rich and poor fen vegetation at 10 cm depth. Specifically, our measurements indicate that poor fen vegetation lowered porewater alkalinity, bicarbonate concentrations and pH. No effects of rich fen vegetation at 10 cm depth on biogeochemistry was measured. However, rich fen litter had a higher mineralization rate than poor fen litter, which increases the influence of minerotrophic water in rich fen habitat. Conclusions These results strengthen our hypothesis that species can drive formation of vegetation mosaics under environmentally homogeneous conditions in a floating fen. Positive intraspecific self‐facilitating mechanisms and negative species interactions could be responsible for a stable coexistence of species, even leading to local ecosystem engineering by the species, explaining the local vegetation mosaic at the microscale level in a floating fen.