Linkages between N turnover and plant community structure in a tundra landscape

Abstract

The spatial distribution of organic soil nitrogen (N) in alpine tundra was studied along a natural environmental gradient, covering five plant communities, at the Latnjajaure Field Station, northern Swedish Lapland. The five communities (mesic meadow, meadow snowbed, dry heath, mesic heath, and heath snowbed) are the dominant types in this region and are differentiated by soil pH. Net N mineralization, net ammonification, and net nitrification were measured using 40-day laboratory incubations based on extractable NH 4 + and NO 3 À . Nitrification enzyme activity (NEA), denitrification enzyme activity (DEA), amino acid concentrations, and microbial respiration were measured for soils from each plant community. The results show that net N mineralization rates were more than three times higher in the meadow ecosystems (mesic meadow 0.7 mg N g À1 OM day À1 and meadow snowbed 0.6 mg N g À1 OM day À1 ) than the heath ecosystems (dry heath 0.2 mg N g À1 OM day À1 , mesic heath 0.1 mg N g À1 OM day À1 and heath snowbed 0.2 mg N g À1 OM day À1 ). The net N mineralization rates were negatively correlated to organic soil C/N ratio (r = À0.652, P < 0.001) and positively correlated to soil pH (r = 0.701, P < 0.001). Net nitrification, inorganic N concentrations, and NEA rates also differed between plant communities; the values for the mesic meadow were at least four times higher than the other plant communities, and the snowbeds formed an intermediate group. Moreover, the results show a different pattern of distribution for individual amino acids across the plant communities, with snowbeds tending to have the highest amino acid N concentrations. The differences between plant communities along this natural gradient also illustrate variations between the dominant mycorrhizal associations in facilitating N capture by the characteristic functional groups of plants.

Plant and microbial responses to nitrogen and phosphorus addition across an elevational gradient in subarctic tundra

“…Within each elevation, the mean distance of each plot to the nearest plot for the same treatment is ;10 m (and the mean distance between the two most distant plots is ;100 m). Due to high spatial heterogeneity over very short distances (often on the order of a few meters) in microtopography and soil fertility characteristic of these communities (Bjo¨rk et al 2007), it is expected that the 10 m distance among plots is sufficient to ensure adequate independence among them (Sundqvist et al 2011a(Sundqvist et al , 2012. Plots at the 500 m elevation were situated in open birch forest immediately below the forest line, and plots at 800 m and 1000 m were devoid of trees.…”

“…Heath vegetation is dominated by evergreen and deciduous dwarf shrubs, while the meadow vegetation is dominated by faster growing plants such as forbs, graminoids, and sedges. The heath vegetation has been shown to have lower soil pH and N availability, but higher P availability and soil fungal-to-bacterial ratios compared to meadow vegetation (Bjo¨rk et al 2007, Eskelinen et al 2009, Sundqvist et al 2011a). Plant and microbial communities for these two vegetation types also display vastly different responses to elevation (Sundqvist et al 2011a).…”

Catchment-scale dissolved carbon concentrations and export estimates across six subarctic streams in northern Sweden

“…approximately 550 m. The soils are mainly upland soils and larger patches of peat soil are only found in the catchment of stream 1 were they account for 7 % of the catchment area. Humus layer thickness is generally less than 10 cm (Björk et al, 2007;Giesler et al, 2012). Podsols are commonly found at lower elevations (< 600 m a.s.l.)…”

Vegetation-Associated Impacts on Arctic Tundra Bacterial and Microeukaryotic Communities

“…The diversity and composition of nematode, testate amoeba, and fungal communities can also be influenced by soil properties (23-25), including acidity, although this may not be true of all microbial metazoans (26). Notwithstanding our appreciation that soil characteristics can affect both bacterial and microeukaryotic communities, the key factors that structure communities of different microbial groups among vegetation types in Arctic tundra are poorly understood.The highly heterogeneous soil conditions in the Arctic tundra mirror the variation in plant community composition over short distances (27,28), and because of this, plant community distributions have proven to be indicators of spatial patterns in underlying microbial communities. Despite important insights, research to date has been based on techniques with relatively low taxonomic resolution and on sampling within rather than between replicate sites of the selected vegetation types.…”

“…The highly heterogeneous soil conditions in the Arctic tundra mirror the variation in plant community composition over short distances (27,28), and because of this, plant community distributions have proven to be indicators of spatial patterns in underlying microbial communities. Despite important insights, research to date has been based on techniques with relatively low taxonomic resolution and on sampling within rather than between replicate sites of the selected vegetation types.…”