Temperature and water controls on vegetation emergence, microbial dynamics, and soil carbon and nitrogen fluxes in a high Arctic tundra ecosystem

Abstract

Summary1. Arctic tundra ecosystems contain 14% of the global soil carbon (C) store which is becoming vulnerable to decomposition. Arctic soil organic matter (SOM) contains large amounts of old, recalcitrant, high molecular weight (MW) C compounds which are protected from decomposition whilst soils remain frozen. Climatic change alters soil temperature and water regimes in the Arctic, however, the impact of these changes on C decomposition and storage is poorly understood. 2. We investigated vegetation emergence, microbial dynamics and nutrient fluxes in response to snow melt on the high Arctic Svalbard archipelago using field and laboratory studies. Using bacterial and archaeal genetic material (16S rRNA) and ammonia-oxidising genes, microbial communities were quantified in transects across the active snow melt front. The effects of soil temperature and water content on SOM decomposition rates were measured using 14 C-labelled low and high MW compounds. 3. Vegetation and below-ground microbial communities, in the field, responded rapidly with peaks in nutrient availability and soil respiration observed within 72 h of snowmelt. Temperature strongly drives early growing season C dynamics in the Arctic. We suggest the nutrient peaks following snowmelt, coupled with higher levels of DNA in the subniveal zone are due to the decomposition of bacteria and archaea from previous years. 4. We show, in the laboratory, when soils thaw, mineralisation of recalcitrant C (high MW) compounds was sensitive to soil water but not to increasing temperatures. In contrast, low MW compounds exhibited sensitivity to both temperature and soil water. We suggest that if future soil water content increases under climate change, high MW compounds could become more susceptible to decomposition, releasing more C to the atmosphere.

A satellite data driven biophysical modeling approach for estimating northern peatland and tundra CO<sub>2</sub> and CH<sub>4</sub> fluxes

“…The observed CH 4 emission sensitivity to surface soil warming may be influenced by cold temperature constraints on CH 4 production in the carbon-rich root zone where organic acids are more abundant (Turetsky et al, 2008;Olefeldt et al, 2013). Lightweight carbon fractions have been shown to be more suscep-tible to mineralization following soil thaw and temperature changes than heavier, more recalcitrant soil organic carbon pools in high-latitude environments (Glanville et al, 2012). However, the depletion of older organic carbon stocks may also become more prevalent in permafrost soils subject to thawing and physiochemical destabilization (Schuur et al, 2009;Hicks Pries et al, 2013a) in the absence of wet, anoxic conditions (Hugelius et al, 2012;Hicks Pries et al, 2013b).…”

Nonlinear temperature sensitivity of enzyme kinetics explains canceling effect—a case study on loamy haplic Luvisol

“…For chemical reactions, the Arrhenius equation predicts exponentially increasing reaction rates with increasing temperature, assuming constant values of activation energy (Kirschbaum, 2000 ; Craine et al, 2010 ; Craine and Gelderman, 2011 ). In nature, however, the decomposition of SOM is mediated by extracellular enzymes, produced by microorganisms (Allison et al, 2010 ; Glanville et al, 2012 ; Zimmermann and Bird, 2012 ; Van Gestel et al, 2013 ). Therefore, deviations from Arrhenius behavior can occur as a consequence of temperature sensitivity of enzyme systems, through enzyme denaturation and proteolysis, for example (Bennett et al, 2008 ; Maire et al, 2013 ; Goyal et al, 2014 ) or by temperature-accelerated desorption of immobilized enzymes (Nannipieri et al, 1996 ; Nielsen et al, 2006 ).…”

Snow vole (Chionomys nivalisMartins) affects the redistribution of soil organic matter and hormone‐like activity in the alpine ecosystem: ecological implications

“…; DeLuca and Zabinski ; Glanville et al. ). Despite this, there is still insufficient information on the role of bioturbation on SOM cycling and properties in alpine soils.…”

“…Alpine soils have received increasing attention in recent years (Geng et al 2012) as they are able to stock soil organic matter (SOM) in critical environmental conditions where low temperatures and low turnover rates of soil organic carbon are expected (Celi et al 2010;Zhuang et al 2010;Budge et al 2011;DeLuca and Zabinski 2011;Glanville et al 2012). Despite this, there is still insufficient information on the role of bioturbation on SOM cycling and properties in alpine soils.…”