15N natural abundance during early and late succession in a middle-European dry acidic grassland |
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Authors: | W Beyschlag S Hanisch S Friedrich A Jentsch & C Werner |
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Institution: | Department of Experimental and Systems Ecology, University of Bielefeld, Bielefeld, Germany; Junior Professorship, Disturbance Ecology and Vegetation Dynamics University of Bayreuth, Bayreuth, Germany |
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Abstract: | δ15N and total nitrogen content of above- and belowground tissues of 13 plant species from two successional stages (open pioneer community and ruderal grass stage) of a dry acidic grassland in Southern Germany were analysed, in order to evaluate whether resource use partitioning by niche separation and N input by N2-fixing legumes are potential determinants for species coexistence and successional changes. Within each stage, plants from plots with different legume cover were compared. Soil inorganic N content, total plant biomass and δ15N values of bulk plant material were significantly lower in the pioneer stage than in the ruderal grass community. The observed δ15N differences were rather species- than site-specific. Within both stages, there were also species-specific differences in isotopic composition between above- and belowground plant dry matter. Species-specific δ15N signatures may theoretically be explained by (i) isotopic fractionation during microbial-mediated soil N transformations; (ii) isotopic fractionation during plant N uptake or fractionation during plant–mycorrhiza transfer processes; (iii) differences in metabolic pathways and isotopic fractionation within the plant; or (iv) partitioning of available N resources (or pools) among plant groups or differential use of the same resources by different species, which seems to be the most probable route in the present case. A significant influence of N2-fixing legumes on the N balance of the surrounding plant community was not detectable. This was confirmed by the results of an independent in situ removal experiment, showing that after 3 years there were no measurable differences in the frequency distribution between plots with and without N2-fixing legumes. |
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Keywords: | 15N natural abundance dry acidic grassland N2-fixing legumes niche differentiation nitrogen resource partitioning stable isotopes |
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