The fate of nitrogen inputs in a warmer alpine treeline ecosystem: a 15N labelling study. (2nd May 2017)

• Record Type: Journal Article
• Authors: Dawes, Melissa A.; Schleppi, Patrick; Hagedorn, Frank
• Editors: Wardle, David
• Is Part Of: Journal of ecology. Volume 105:Number 6(2017:Nov.)
• Page Start: 1723
• Page End: 1737
• Publication Date: 2017-05-02
• Subjects: δ13C -- δ15N -- ammonium -- climate change -- glycine -- plant–soil (below‐ground) interactions -- stable isotope -- Vaccinium gaultherioides -- Vaccinium myrtillus; Plant ecology -- Periodicals; 577.05
• DOI: 10.1111/1365-2745.12780
• Languages: English
• ISSNs: 0022-0477

Abstract

Summary: Global warming may accelerate nitrogen (N) transformations in the soil, with potentially large effects in N‐poor high‐elevation ecosystems. To gain insight into the partitioning of inorganic and organic N inputs within the plant–soil system and how warming influences these patterns, we applied a 15 N label ( 15 NH4 Cl or 15 N‐glycine) shortly after snowmelt during the sixth year of experimental soil warming (+4 °C) at treeline in the Swiss Alps. Seven weeks after labelling, approximately 60% of the applied label remained in the soil organic layer to 10 cm depth, whereas label recovery summed over all measured plant pools was <10% of the added label. Soil warming led to a weaker Δ 15 N signal in plants and no change in the amount of added label recovered in plants. This 15 N dilution resulted from a greater N pool size of some plant species in warmed plots as well as enhanced availability of (unlabelled) N under warming. Temporal dynamics of foliar Δ 15 N in dominant dwarf shrub species suggested that these plants primarily take up N early in the season. In a subset of plots labelled with 13 C‐enriched glycine (U‐ 13 C2 ‐ 15 N‐glycine), the labelled glycine was mineralized rapidly, with approximately 50% of the applied 13 C respired as CO2 during the first 99 h, suggesting that effects of warmer soils on N dynamics in this treeline system are only slightly modulated by the preferences of different plant species for inorganic and organic N forms. Synthesis . Plants growing in warmer soils acquired more unlabelled, soil‐derived N in the sixth year of treatment, implying a sustained increase in N mineralization and availability in alpine treeline ecosystems with higher soil temperatures predicted for the future. Wide variation in the ability of plant species and functional groups to compete for early‐summer N inputs means that there is a feedback between plant community shifts and N dynamics under environmental change at the treeline. Abstract : We applied a 15 N label after snowmelt during the sixth year of soil warming at the Swiss treeline. Plants growing in warmer soils acquired more unlabelled, soil‐derived 15 N, implying a sustained increase in N availability in treeline ecosystems with warming. Variation in the ability of plant groups to compete for early‐summer N inputs suggests a feedback between plant community shifts and N dynamics under environmental change.