Initial Stages of Tundra Shrub Litter Decomposition May Be Accelerated by Deeper Winter Snow But Slowed Down by Spring Warming

Abstract

The Arctic climate is projected to change during the coming century, with expected higher air temperatures and increased winter snowfall. These climatic changes might alter litter decomposition rates, which in turn could affect carbon (C) and nitrogen (N) cycling rates in tundra ecosystems. However, little is known of seasonal climate change effects on plant litter decomposition rates and N dynamics, hampering predictions of future arctic vegetation composition and the tundra C balance. We tested the effects of snow addition (snow fences), warming (open top chambers), and shrub removal (clipping), using a full-factorial experiment, on mass loss and N dynamics of two shrub tissue types with contrasting quality: deciduous shrub leaf litter (Salix glauca) and evergreen shrub shoots (Cassiope tetragona). We performed a 10.5-month decomposition experiment in a low-arctic shrub tundra heath in WestGreenland. Field incubations started in late fall, with harvests made after 249, 273, and 319 days of field incubation during early spring, summer and fall of the next year, respectively. We observed a positive effect of deeper snow on winter mass loss which is considered a result of observed higher soil winter temperatures and corresponding increased winter microbial litter decomposition in deep-snow plots. In contrast, warming reduced litter mass loss during spring, possibly because the dry spring conditions might have dried out the litter layer and thereby limited microbial litter decomposition. Shrub removal had a small positive effect on litter mass loss for C. tetragona during summer, but not for S. glauca. Nitrogen dynamics in decomposing leaves and shoots were not affected by the treatments but did show differences in temporal patterns between tissue types: there was a net immobilization of N by C. tetragona shoots after the winter incubation, while S. glauca leaf N-pools were unaltered over time. Our results support the widely hypothesized positive linkage between winter snow depth and litter decomposition rates in tundra ecosystems, but our results do not reveal changes in N dynamics during initial decomposition stages. Our study also shows contrasting impacts of spring warming and snow

Leaf anatomy, BVOC emission and CO2exchange of arctic plants following snow addition and summer warming

“…Both sides of the snow fence also had a year-round installed polycarbonate hexagon open-top chamber (OTC; bottom diameter 150 cm, height 35 cm). Continuous temperature measurements showed that the OTCs significantly increased the surface air temperature by 2Á7 C during the summer of 2013, but not during the winter of 2012-13 (Blok et al, 2016). With six replicates of the treatments C, S, OTC and the combined SþOTC, the total number of treatment plots used in this study was 24.…”

“…S1). Snow remained in the snow addition treatment (S) until mid-June, whereas the control treatment (C) was close to snow-free (362 cm) following a spring warming event in late March 2013 (Blok et al, 2016). Both sides of the snow fence also had a year-round installed polycarbonate hexagon open-top chamber (OTC; bottom diameter 150 cm, height 35 cm).…”

“…The experiment has been described in detail by Blok et al (2016). The experiment consisted of factorial passive warming and passive snow addition treatments replicated in six blocks, each with a snow fence (14Á7 m long and 1Á5 m high).…”

“…In colder regions, a greater snow depth is expected as a result of increased precipitation rates during winter (Collins et al, 2013). The insulating property of the snowpack increases the soil temperature and can thereby lead to increased litter turnover rates (Blok et al, 2016), greater nutrient availability and higher soil moisture concentrations (Wipf and Rixen, 2010;Semenchuk et al, 2015). Furthermore, greater snow depth may delay snowmelt and the start of the growing season (Wipf and Rixen, 2010).…”

Water flow in the active layer along an arctic slope – An investigation based on a field campaign and model simulations

“…The deepening of the active layer will change the flow and transport pattern and typically lead to longer travel paths and times (Frey and McClelland, 2009;Frampton and Destouni, 2015). An ecological effect is related to the release and subsequent migration of inorganic nitrogen stored in the perennially frozen ground (Elberling et al, 2010) or from winter decomposition (Blok et al, 2016). These two processes occur at different times during the year and release nitrogen at different depths in the active layer.…”