Distinct fungal and bacterial δ13C signatures as potential drivers of increasing δ13C of soil organic matter with depth

Kohl, Leonie; Laganière, Jérôme; Edwards, Kate A.; Billings, Sharon A.; Morrill, Penny L.; Biesen, Geert Van; Ziegler, Susan E.

doi:10.1007/s10533-015-0107-2

Cited by 58 publications

(76 citation statements)

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“…1) is too large to be driven by aging of the material within the top 5 cm only. Irrespective of the reason for the gradual enrichment of bulk-soil OM with aging, 13 C enrichment in the range as demonstrated in the presented study require cycling of OM through several soil horizons (e.g., Arrouays et al 1995, van Kessel et al 2006, Yoneyama et al 2006, Kohl et al 2015. First findings from terrestrial systems demonstrate order of magnitude differences in relative fungal abundance (1-55%) to impact the d 13 C of bulk-soil OM in a range of only <3& (Kohl et al 2015).…”

Section: Site Effects On Microbial Structure and Functionmentioning

confidence: 49%

Top‐down control of carbon sequestration: grazing affects microbial structure and function in salt marsh soils

Mueller

Granse

Nolte

et al. 2017

Ecological Applications

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Tidal wetlands have been increasingly recognized as long-term carbon sinks in recent years. Work on carbon sequestration and decomposition processes in tidal wetlands focused so far mainly on effects of global-change factors such as sea-level rise and increasing temperatures. However, little is known about effects of land use, such as livestock grazing, on organic matter decomposition and ultimately carbon sequestration. The present work aims at understanding the mechanisms by which large herbivores can affect organic matter decomposition in tidal wetlands. This was achieved by studying both direct animal-microbe interactions and indirect animal-plant-microbe interactions in grazed and ungrazed areas of two long-term experimental field sites at the German North Sea coast. We assessed bacterial and fungal gene abundance using quantitative PCR, as well as the activity of microbial exo-enzymes by conducting fluorometric assays. We demonstrate that grazing can have a profound impact on the microbial community structure of tidal wetland soils, by consistently increasing the fungi-to-bacteria ratio by 38-42%, and therefore potentially exerts important control over carbon turnover and sequestration. The observed shift in the microbial community was primarily driven by organic matter source, with higher contributions of recalcitrant autochthonous (terrestrial) vs. easily degradable allochthonous (marine) sources in grazed areas favoring relative fungal abundance. We propose a novel and indirect form of animal-plant-microbe interaction: top-down control of aboveground vegetation structure determines the capacity of allochthonous organic matter trapping during flooding and thus the structure of the microbial community. Furthermore, our data provide the first evidence that grazing slows down microbial exo-enzyme activity and thus decomposition through changes in soil redox chemistry. Activities of enzymes involved in C cycling were reduced by 28-40%, while activities of enzymes involved in N cycling were not consistently affected by grazing. It remains unclear if this is a trampling-driven direct grazing effect, as hypothesized in earlier studies, or if the effect on redox chemistry is plant mediated and thus indirect. This study improves our process-level understanding of how grazing can affect the microbial ecology and biogeochemistry of semi-terrestrial ecosystems that may help explain and predict differences in C turnover and sequestration rates between grazed and ungrazed systems.

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Section: Site Effects On Microbial Structure and Functionmentioning

confidence: 49%

Top‐down control of carbon sequestration: grazing affects microbial structure and function in salt marsh soils

Mueller

Granse

Nolte

et al. 2017

Ecological Applications

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“…, Kohl et al. ). It is, however, unclear if such fractionation processes also occur in tidal‐wetland soils to a degree that mixing‐model calculations would be considerably biased (Kelleway et al.…”

Section: Discussionmentioning

confidence: 99%

Assessing the long‐term carbon‐sequestration potential of the semi‐natural salt marshes in the European Wadden Sea

et al. 2019

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Salt marshes and other blue carbon ecosystems have been increasingly recognized for their carbon (C)-sink function. Yet, an improved assessment of organic carbon (OC) stocks and C-sequestration rates is still required to include blue C in C-crediting programs. Particularly, factors inducing variability in the permanence of sequestration and allochthonous contributions to soil OC stocks require an improved understanding. This study evaluates the potential for long-term C sequestration in the semi-natural salt marshes of the European Wadden Sea (WS), conducting deep (1.3 m) down-core OC-density assessments in sites with known site histories and accretion records. Because these young marshes have developed from tidal-flat ecosystems and have undergone rapid succession during the last 80-120 yr, the identification of different ecosystem stages down-core was crucial to interpret possible changes in OC density. This was conducted based on the down-core distribution of different foraminiferal taxa and grain sizes. Comparisons of historic and recent accretion rates were conducted to understand possible effects of accretion rate on down-core changes in OC density. d 13 C in OC was used to assess the origin of accumulated OC (autochthonous vs. allochthonous sources). We show that large amounts of short-term accumulated OC are lost down-core in the well-aerated marsh soils of the WS region and thus emphasize the importance of deep sampling to avoid overestimation of C sequestration. Despite steep declines in OC-density downcore, minimum values of OC density in the salt-marsh soils were considerably higher than those of the former tidal-flat sediments that the marshes were converted from, illustrating the greater C-sequestration potential of the vegetated ecosystem. However, our data also suggest that marine-derived allochthonous OC makes up a large fraction of the effectively, long-term preserved OC stock, whereas atmospheric CO 2 removal by marsh vegetation contributes relatively little. The implication of this finding for C-crediting approaches in blue C ecosystems has yet to be clarified.

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“…1). The atmospheric depletion of 13 C (Suess effect), the accumulation of 13 C enriched microbial products (Lerch et al, 2011;Accoe et al, 2002), higher potential soil respiration (unpublished data), increasing fungal: bacterial ratios (Wallander et al, 2009;Kohl et al, 2015), greater root biomass (Hansson et al, 2010;Peri et al, 2015) and decreasing pH (Hall and Silver, 2013) might have combined to enhance δ 13 C depth trends with proceeding time of forest continuity (Fig. 2).…”

Section: Discussionmentioning

confidence: 99%

Three decades following afforestation are sufficient to yield δ¹³C depth profiles

Brunn

Brodbeck

Oelmann

2017

J. Plant Nutr. Soil Sci.

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Vertical gradients in stable carbon isotope ratios (δ13C) in soil profiles can serve to approximate decomposition of organic matter under field conditions. This study tested the time (0, 30, and ≥ 150 y) required for the development of vertical δ13C profiles in topsoil by comparing arable, afforested and continuously forested sites, and showed that three decades following afforestation of former cropland are sufficient to develop distinct δ13C depth profiles.

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Distinct fungal and bacterial δ13C signatures as potential drivers of increasing δ13C of soil organic matter with depth

Abstract: Soil microbial biomass is a key source of soil organic carbon (SOC), and the increasing proportion of microbially derived SOC is thought to drive the enrichment of 13 C during SOC decomposition. Yet, little is known about how the d 13

Cited by 58 publications

References 50 publications

Top‐down control of carbon sequestration: grazing affects microbial structure and function in salt marsh soils

Top‐down control of carbon sequestration: grazing affects microbial structure and function in salt marsh soils

Assessing the long‐term carbon‐sequestration potential of the semi‐natural salt marshes in the European Wadden Sea

Three decades following afforestation are sufficient to yield δ¹³C depth profiles

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Distinct fungal and bacterial δ13C signatures as potential drivers of increasing δ13C of soil organic matter with depth

Abstract: Soil microbial biomass is a key source of soil organic carbon (SOC), and the increasing proportion of microbially derived SOC is thought to drive the enrichment of 13 C during SOC decomposition. Yet, little is known about how the d 13

Cited by 58 publications

References 50 publications

Top‐down control of carbon sequestration: grazing affects microbial structure and function in salt marsh soils

Top‐down control of carbon sequestration: grazing affects microbial structure and function in salt marsh soils

Assessing the long‐term carbon‐sequestration potential of the semi‐natural salt marshes in the European Wadden Sea

Three decades following afforestation are sufficient to yield δ13C depth profiles

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Product

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Three decades following afforestation are sufficient to yield δ¹³C depth profiles