Soil warming opens the nitrogen cycle at the alpine treeline. (21st June 2016)

• Record Type: Journal Article
• Authors: Dawes, Melissa A.; Schleppi, Patrick; Hättenschwiler, Stephan; Rixen, Christian; Hagedorn, Frank
• Is Part Of: Global change biology. Volume 23:Number 1(2017)
• Page Start: 421
• Page End: 434
• Publication Date: 2016-06-21
• Subjects: dissolved organic nitrogen -- European larch -- Larix decidua -- mountain pine -- Pinus uncinata -- stable isotope -- Vaccinium gaultherioides -- Vaccinium myrtillus; Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.13365
• Languages: English
• ISSNs: 1354-1013

Abstract

Abstract: Climate warming may alter ecosystem nitrogen (N) cycling by accelerating N transformations in the soil, and changes may be especially pronounced in cold regions characterized by N‐poor ecosystems. We investigated N dynamics across the plant–soil continuum during 6 years of experimental soil warming (2007–2012; +4 °C) at a Swiss high‐elevation treeline site (Stillberg, Davos; 2180 m a.s.l.) featuring Larix decidua and Pinus uncinata . In the soil, we observed considerable increases in the NH 4 + pool size in the first years of warming (by >50%), but this effect declined over time. In contrast, dissolved organic nitrogen (DON) concentrations in soil solutions from the organic layer increased under warming, especially in later years (maximum of +45% in 2012), suggesting enhanced DON leaching from the main rooting zone. Throughout the experimental period, foliar N concentrations showed species‐specific but small warming effects, whereas δ 15 N values showed a sustained increase in warmed plots that was consistent for all species analysed. The estimated total plant N pool size at the end of the study was greater (+17%) in warmed plots with Pinus but not in those containing Larix, with responses driven by trees. Irrespective of plot tree species identity, warming led to an enhanced N pool size of Vaccinium dwarf shrubs, no change in that of Empetrum hermaphroditum (dwarf shrub) and forbs, and a reduction in that of grasses, nonvascular plants, and fine roots. In combination, higher foliar δ 15 N values and the transient response in soil inorganic N indicate a persistent increase in plant‐available N and greater cumulative plant N uptake in warmer soils. Overall, greater N availability and increased DON concentrations suggest an opening of the N cycle with global warming, which might contribute to growth stimulation of some plant species while simultaneously leading to greater N losses from treeline ecosystems and possibly other cold biomes.