title: Differential responses of two wetland graminoids to high ammonium at different pH values.
abstract: Enhanced soil ammonium (NH4+) concentrations in wetlands often lead to graminoid dominance, but species composition is highly variable. Although NH4+ is readily taken up as a nutrient, several wetland species are known to be sensitive to high NH4+ concentrations or even suffer toxicity, particularly at low soil pH. More knowledge about differential graminoid responses to high NH4+ availability in relation to soil pH can help to better understand vegetation changes. The responses of two wetland graminoids, Juncus acutiflorus and Carex disticha, to high (2 mmol·l(-1) ) versus control (20 μmol·l(-1) ) NH4+ concentrations were tested in a controlled hydroponic set up, at two pH values (4 and 6). A high NH4+ concentration did not change total biomass for these species at either pH, but increased C allocation to shoots and increased P uptake, leading to K and Ca limitation, depending on pH treatment. More than 50% of N taken up by C. disticha was invested in N-rich amino acids with decreasing C:N ratio, but only 10% for J. acutiflorus. Although both species appeared to be well adapted to high NH4+ loadings in the short term, C. disticha showed higher classic detoxifying responses that are early warning indicators for decreased tolerance in the long term. In general, the efficient aboveground biomass allocation, P uptake and N detoxification explain the competitive strength of wetland graminoids at the expense of overall biodiversity at high NH4+ loading. In addition, differential responses to enhanced NH4+ affect interspecific competition among graminoids and lead to a shift in vegetation composition.
authors.affiliation: B-WARE Research Centre, Radboud University Nijmegen, Nijmegen, the Netherlands.|Institute for Water and Wetland Research, Department of Aquatic Ecology and Environmental Biology, Radboud University Nijmegen, Nijmegen, the Netherlands.
authors.forename: J M H
authors.initials: JM
authors.lastname: van Diggelen
authors.affiliation: B-WARE Research Centre, Radboud University Nijmegen, Nijmegen, the Netherlands.|Institute for Water and Wetland Research, Department of Aquatic Ecology and Environmental Biology, Radboud University Nijmegen, Nijmegen, the Netherlands.
authors.forename: A J P
authors.initials: AJ
authors.lastname: Smolders
authors.affiliation: Institute for Water and Wetland Research, Department of Experimental Plant Ecology, Radboud University Nijmegen, Nijmegen, the Netherlands.
authors.forename: E J W
authors.initials: EJ
authors.lastname: Visser
authors.affiliation: B-WARE Research Centre, Radboud University Nijmegen, Nijmegen, the Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: Hicks
authors.affiliation: Institute for Water and Wetland Research, Department of Aquatic Ecology and Environmental Biology, Radboud University Nijmegen, Nijmegen, the Netherlands.
authors.forename: J G M
authors.initials: JG
authors.lastname: Roelofs
authors.affiliation: Institute for Water and Wetland Research, Department of Aquatic Ecology and Environmental Biology, Radboud University Nijmegen, Nijmegen, the Netherlands.
authors.forename: L P M
authors.initials: LP
authors.lastname: Lamers
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D064751:Ammonium Compounds / Q000494:pharmacology*; D018533:Biomass; D006863:Hydrogen-Ion Concentration; D019684:Magnoliopsida / Q000187:drug effects / Q000502:physiology*; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism; D053833:Wetlands
chemical_list: D000596:Amino Acids; D064751:Ammonium Compounds; D009566:Nitrates; D009584:Nitrogen
keywords: Amino acids; ammonium toxicity; carbon allocation; graminoid dominance; nitrogen availability; pH; stress responses; wetlands