Fast Responses of Root Dynamics to Increased Snow Deposition and Summer Air Temperature in an Arctic Wetland

Abstract

In wet tundra ecosystems, covering vast areas of the Arctic, the belowground plant biomass exceeds the aboveground, making root dynamics a crucial component of the nutrient cycling and the carbon (C) budget of the Arctic. In response to the projected climatic scenarios for the Arctic, namely increased temperature and changes in precipitation patterns, root dynamics may be altered leading to significant changes in the net ecosystem C budget. Here, we quantify the single and combined effects of 1 year of increased winter snow deposition by snow fences and summer warming by open-top chambers (OTCs) on root dynamics in a wetland at Disko Island (West Greenland). Based on ingrowth bags, snow accumulation decreased root productivity by 42% in the 0–15 cm soil depth compared to ambient conditions. Over the growing season 2014, minirhizotron observations showed that root growth continued until mid-September in all treatments, and it peaked between the end of July and mid-August. During the season, plots exposed to experimental warming showed a significant increase in root number during September (between 39 and 53%) and a 39% increase in root length by the beginning of September. In addition, a significant reduction of root diameter (14%) was observed in plots with increased snow accumulation. Along the soil profile (0–40 cm) summer warming by OTCs significantly increased the total root length (54%), root number (41%) and the root growth in the 20–30 cm soil depth (71%). These results indicate a fast response of this ecosystem to changes in air temperature and precipitation. Hence, on a short-term, summer warming may lead to increased root depth and belowground C allocation, whereas increased winter snow precipitation may reduce root production or favor specific plant species by means of reduced growing season length or increased nutrient cycling. Knowledge on belowground root dynamics is therefore critical to improve the estimation of the C balance of the Arctic.

Foraging deeply: Depth‐specific plant nitrogen uptake in response to climate‐induced N‐release and permafrost thaw in the High Arctic

“…The depth‐specific pattern of root biomass corresponded well to findings from other permafrost ecosystems (Christiansen et al., 2012; D'Imperio et al., 2018; Hewitt et al., 2018; Keuper et al., 2017), where the majority of root biomass occurs in the top 30 cm. Nonetheless, we detected roots throughout the soil profile, even reaching the permafrost thaw front (Figure 1).…”

“…In the High Arctic, plant growth is limited by the short growing season. However, the below‐ground growing season may be longer than the above‐ground (Blume‐Werry, Wilson, Kreyling, & Milbau, 2016; D'Imperio et al., 2018), and for N‐limited high arctic plants, the ability to remain active past the peak growing season is a competitive strength in order to take advantage of late‐season N pools (Iversen et al., 2015). By injecting isotopically labelled 15 N into the soil at the time of maximum active layer depth, we simulated N pulse from permafrost thaw and accrual of plant available N as plant demand and competition lessen in the autumn.…”

“…In the High Arctic, plant growth is limited by the short growing season. However, the below-ground growing season may be longer than the above-ground (Blume-Werry, Wilson, Kreyling, & Milbau, 2016;D'Imperio et al, 2018), and for N-limited high arctic plants, the ability to remain active past the peak growing season is a competitive strength in order to take advantage of late-season N pools (Iversen et al, 2015). By (Figure 2a).…”

“…In the top‐soil, higher temperatures induced by enhanced snow cover in winter and warming in summer accelerate microbial decomposition and N mineralization (Mörsdorf et al., 2019; Salmon et al., 2016; Schimel, Bilbrough, & Welker, 2004; Semenchuk et al., 2015). Increased N availability in upper soil layers is particularly important for arctic vegetation, where the majority of root biomass is concentrated in the top‐soil (Christiansen, Svendsen, Schmidt, & Michelsen, 2012; D'Imperio, Arndal, Nielsen, Elberling, & Schmidt, 2018; Hewitt, Taylor, Genet, McGuire, & Mack, 2018; Keuper et al., 2017). In the deep‐soil, a second process of nutrient release occurs.…”

Estimating meltwater retention and associated nitrate redistribution during snowmelt in an Arctic tundra landscape*

“…Nitrogen (N) in a plant available form is a key component for these responses since N is considered a limiting factor for plant growth in the Arctic (Shaver et al 2006). Future warming and changes in precipitation patterns are likely to catalyze mineralization of stored N, but also potentially increase other sources such as atmospheric deposition, which could lead to alterations in Arctic vegetation dynamics (Rousk et al 2017a, Bokhorst et al 2018, D'Imperio et al 2018. Main sources of plantavailable N at catchment scale in most pristine Arctic ecosystems include redistributed internal N from mineralization of soil organic matter and inputs from fauna, and external input from atmospheric deposition and N 2 fixation (Skrzypek et al 2015).…”