Labile carbon limits late winter microbial activity near Arctic treeline

Patrick F Sullivan,Madeline C Stokes,Cameron K Mcmillan,Michael N Weintraub

doi:10.1038/s41467-020-17790-5

Patrick F Sullivan, Madeline C Stokes + Show 2 more

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https://doi.org/10.1038/s41467-020-17790-5

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Abstract

Soil microbial communities remain active during much of the Arctic winter, despite deeply frozen soils. Overwinter microbial activity affects the global carbon (C) budget, nutrient cycling, and vegetation composition. Microbial respiration is highly temperature sensitive in frozen soils, as liquid water and solute availability decrease rapidly with declining temperature. Climate warming and changes in snowpack are leading to warmer Arctic winter soils. Warmer winter soils are thought to yield greater microbial respiration of available C, greater overwinter CO2 efflux and greater nutrient availability to plants at thaw. Using field and laboratory observations and experiments, we demonstrate that persistently warm winter soils can lead to labile C starvation and reduced microbial respiration, despite the high C content of most Arctic soils. If winter soils continue to warm, microbial C limitation will reduce expected CO2 emissions and alter soil nutrient cycling, if not countered by greater labile C inputs.

Highlights

Soil microbial communities remain active during much of the Arctic winter, despite deeply frozen soils
Our field observations, field experimentation, and laboratory incubations clearly demonstrate that relatively warm winter soils at our study sites near the Arctic treeline in the western Brooks Range can lead to pervasive labile C limitation of microbial respiration
This finding has important implications for current estimates and projections of Pan-Arctic C budgets with warming, while adding complexity and uncertainty to our understanding of relationships among vegetation, snow and soil nutrient cycling at high latitudes

Summary

Introduction

Soil microbial communities remain active during much of the Arctic winter, despite deeply frozen soils. 1234567890():,; The importance of overwinter microbial activity to ecosystem C budgets was first recognized in the sub-alpine forests of Colorado and Wyoming, where relatively deep and often early developing snowpacks maintain soil temperatures of −3 to 0 °C throughout the winter[1] These lightly frozen to unfrozen soils contain substantial amounts of liquid water, because solutes depress the freezing point, minimizing important physical constraints to microbial activity that are present in deeply frozen soils[2]. A vegetation clipping experiment in Arctic tundra of northern Sweden showed that overwinter microbial respiration is primarily associated with recently fixed plant C, rather than the large pool of bulk soil organic C14,15 In this experiment, winter CO2 efflux was much lower and less temperature sensitive in clipped than unclipped plots. At treeline in northern Sweden, labile C inputs from mountain birch trees were shown to stimulate microbial respiration and decomposition of older soil organic matter, thereby reducing soil C stocks relative to the tundra[16]

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