Snowpack influences spatial and temporal soil nitrogen dynamics in a western U.S. montane forested watershed

Yuriko Yano,Claire Qubain,Kelsey Jencso,Jia Hu,Zach Holyman

doi:10.1002/ecs2.2794

Yuriko Yano, Claire Qubain + Show 3 more

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https://doi.org/10.1002/ecs2.2794

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Abstract

AbstractDeclines in winter snowpack have increased the severity of summer droughts in western U.S. forests, with the potential to also impact soil available nitrogen (N). To understand how snowpack controls spatiotemporal N availability, we examined seasonal N dynamics across elevation, aspect, and topographic position (hollow vs. slope) in a forested watershed in the northern Rocky Mountains. As expected, peak snow‐water equivalent (SWE) was generally greater at higher elevations and on north‐facing aspects. However, the effects of topographic position and snowdrift led to variability in snow accumulation at smaller spatial scales. Spatial patterns of the snowpack, in turn, influenced soil moisture and temperature, with greater SWE leading to generally higher soil moisture levels during the summer and smaller temperature fluctuations throughout the year. Wetter conditions in spring or fall generally supported greater inorganic N pools, but at the driest locations (low‐elevation slope), pulses of N mineralization in summer may have played important roles in overall N dynamics. More importantly, soil moisture during the summer appeared to be more influenced by antecedent snowpack from the previous year than by current‐year summer rain. Subsequently, N mineralization under snowpack may be strongly influenced by soil moisture and temperature conditions from the previous fall, before snowpack accumulation. Together, our results indicate that snowpack strongly influences N dynamics beyond the current growing season in western coniferous forests through mediation of soil moisture and temperature, and suggest that further decline in winter snowpack may affect these forests through constraints in both water and N availability.

Highlights

In temperate forests, nitrogen (N) is often considered to be the most common limiting nutrient (Vitousek and Howarth 1991), and many experimental studies demonstrate increases in aboveground productivity with increased N availability
While this suggests that snowpack declines and earlier snowmelt under warmer climate can alter seasonal N availability, we currently lack a basic understanding of N dynamics at the landscape scale to evaluate these potential outcomes
Most of our current knowledge is derived from plot-scale studies that have focused on the insulative effect of snowpack on N dynamics mediated by soil microbes because low soil temperature is thought to be the main factor limiting microbial activity in many mesic snowdominated ecosystems (Brooks et al 1998, 2011, Schimel et al 2004, Groffman et al 2009, Duran et al 2014)

Summary

Introduction

In temperate forests, nitrogen (N) is often considered to be the most common limiting nutrient (Vitousek and Howarth 1991), and many experimental studies demonstrate increases in aboveground productivity with increased N availability (summarized in LeBauer and Treseder 2008). While this suggests that snowpack declines and earlier snowmelt under warmer climate can alter seasonal N availability, we currently lack a basic understanding of N dynamics at the landscape scale to evaluate these potential outcomes. Most of our current knowledge is derived from plot-scale studies that have focused on the insulative effect of snowpack on N dynamics mediated by soil microbes because low soil temperature is thought to be the main factor limiting microbial activity in many mesic snowdominated ecosystems (Brooks et al 1998, 2011, Schimel et al 2004, Groffman et al 2009, Duran et al 2014)

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