Abstract
Rising temperatures in the Arctic have led to the thawing of tundra soils, which is rapidly changing terrain, hydrology, and plant and microbial communities, causing hotspots of biogeochemical activity across the landscape. Despite this, little is known about how nutrient-rich low molecular weight dissolved organic matter (LMW DOM) varies within and across tundra ecosystems. Using a high-resolution nano-liquid chromatography-mass spectrometry (LC/MS) approach, we characterized the composition and availability of LMW DOM from high-centered polygons (HCP) and low-centered polygons (LCP) with Eriophorum angustifolium or Carex aquatilis as the dominant vegetation. Over 3000 unique features (i.e., discrete mass/charge ions) were detected; 521 were identified as differentially abundant between polygonal types and 217 were putatively annotated using high mass accuracy MS data. While polygon type was a strong predictor of LMW DOM composition and availability, vegetation and soil depth were also important drivers. Extensive evidence was found for enhanced microbial processing at the LCP sites, which were dominated by Carex plant species. We detected significant differences between polygon types with varying aboveground landscape features or properties, and hotspots of biogeochemical activity, indicating LMW DOM, as quantified by untargeted exometabolomics, provides a window into the dynamic complex interactions between landscape topography, vegetation, and organic matter cycling in Arctic polygonal tundra soils.
Highlights
The Arctic is warming at least twice as fast as any other landscape on the planet and stores nearly half the Earth’s terrestrial carbon (C) in soil organic matter (SOM) associated with permafrost soils [1,2,3]
Features that matched to multiple hits in a database or multiple formulas were manually scrutinized in an iterative approach by assessing high-resolution mass spectral data for consistent fragmentation profiles. Given that this was the first application of this untargeted exometabolomics technique across multiple Arctic sampling sites, we began with an evaluation of the analytical performance of the approach
While the total number of features varied some between soil cores, overall, hydrophilic interaction chromatography (HILIC) (+) detected the greatest number of high-quality features (HQFs) across the four cores with 3929 (34.9%) followed by RP (+) with 3618 (32.1%), HILIC (−) with 2170 (19.3%), and RP (−) with 1541 (13.7%) (Table 1)
Summary
The Arctic is warming at least twice as fast as any other landscape on the planet and stores nearly half the Earth’s terrestrial carbon (C) in soil organic matter (SOM) associated with permafrost soils [1,2,3]. Predicting where (hotspots) or when (hot moments) this C loss is most likely to occur across the Arctic landscape, depends on multiple interacting factors. These include landscape heterogeneity [11,12,13] and the associated shifts in hydrology (topography) [14,15], Soil Syst. 2021, 5, 10 occur across the Arctic landscape, depends on multiple interacting fa2cotof 1r9s These include landscape heterogeneity [11,12,13] and the associated shifts in hydrology (topography) [14,15], vegetation [16,17], microbial community composition [18]. Furthervmegoereta, ttihoenc[h1e6m,1i7c]a,lmcoicmropboisailticoonmomf SuOnMity, ocroimtspinohsietrioennt[a1v8a].ilaFbuilritthyetromsooriel ,mtihcerocbhieaml ciocmalcmomunpiotiseisti,ovnaroiefsSsOtrMon, golryiwtsitihnhlaenrednstcaapveaihlaebteilriotygetnoesitoyil[1m9i–c2r1o]b, iaanl dcotmhismmunoilteiceus,lavra-srciaesle sitnrfoonrgmlyatwiointhislacnudrsrecanptley hpeotoerrolygeunnediteyrs[t1o9o–d21a]n, danpdotohrilsy mchoaleraccutlearri-zsecdaleininpfroorcmesast-iboanseisd cmurordeenltsly[2p2o–o2r4l]y. understood and poorly characterized in process-based models [22,23,24]
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