Isotopic niche (δ<sup>13</sup>С and δ<sup>15</sup>N values) of soil macrofauna in temperate forests

Korobushkin, Danııl I.; Gongalsky, Konstantin B.; Tiunov, Alexei V.

doi:10.1002/rcm.6903

Cited by 38 publications

(22 citation statements)

References 56 publications

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“…The results suggest that food chains in the mineral soil are longer than in the litter layer. Two other studies showed that the isotopic niche of Collembola in temperate forests (based on δ 13 C and δ 15 N ranges) is at least as wide as that of macrofauna species, suggesting similar variations in the diet of these two groups (Korobushkin, Gongalsky & Tiunov, ; Potapov et al ., ). This is supported by data compiled for this study (Section IX).…”

Section: Trophic Niche Metricsmentioning

confidence: 95%

“…Normalized δ values (often denoted as Δ or ϵ values) of soil animals from different ecosystems can then be compared (Klarner et al ., ; Potapov et al ., ). This normalization is crucial for δ 15 N values, but may not be needed for δ 13 C values (Korobushkin et al ., ). In some cases mineral soil rather than litter δ values has been used as the baseline to normalize animal stable isotope composition (Crotty et al ., ; Cronin et al ., ).…”

Section: Baseline Normalization Across Ecosystemsmentioning

confidence: 97%

“…Typically, soil invertebrates are enriched in 13 C by about 2-5‰ relative to the leaf litter (Schmidt et al, 2004;Okuzaki et al, 2009;Pollierer et al, 2009). This 13 C enrichment ('detrital shift') is likely caused by acquiring C from saprotrophic fungi and bacteria (Potapov et al, 2013;Korobushkin et al, 2014;Hyodo, 2015). In turn, microbial enrichment in 13 C relative to the litter may be driven by selective use of certain organic compounds (Dijkstra et al, 2006).…”

Section: Trophic Enrichmentmentioning

confidence: 99%

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Uncovering trophic positions and food resources of soil animals using bulk natural stable isotope composition

2018

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Despite the major importance of soil biota in nutrient and energy fluxes, interactions in soil food webs are poorly understood. Here we provide an overview of recent advances in uncovering the trophic structure of soil food webs using natural variations in stable isotope ratios. We discuss approaches of application, normalization and interpretation of stable isotope ratios along with methodological pitfalls. Analysis of published data from temperate forest ecosystems is used to outline emerging concepts and perspectives in soil food web research. In contrast to aboveground and aquatic food webs, trophic fractionation at the basal level of detrital food webs is large for carbon and small for nitrogen stable isotopes. Virtually all soil animals are enriched in C as compared to plant litter. This 'detrital shift' likely reflects preferential uptake of C-enriched microbial biomass and underlines the importance of microorganisms, in contrast to dead plant material, as a major food resource for the soil animal community. Soil organic matter is enriched in N and C relative to leaf litter. Decomposers inhabiting mineral soil layers therefore might be enriched in N resulting in overlap in isotope ratios between soil-dwelling detritivores and litter-dwelling predators. By contrast, C content varies little between detritivores in upper litter and in mineral soil, suggesting that they rely on similar basal resources, i.e. little decomposed organic matter. Comparing vertical isotope gradients in animals and in basal resources can be a valuable tool to assess trophic interactions and dynamics of organic matter in soil. As indicated by stable isotope composition, direct feeding on living plant material as well as on mycorrhizal fungi is likely rare among soil invertebrates. Plant carbon is taken up predominantly by saprotrophic microorganisms and channelled to higher trophic levels of the soil food web. However, feeding on photoautotrophic microorganisms and non-vascular plants may play an important role in fuelling soil food webs. The trophic niche of most high-rank animal taxa spans at least two trophic levels, implying the use of a wide range of resources. Therefore, to identify trophic species and links in food webs, low-rank taxonomic identification is required. Despite overlap in feeding strategies, stable isotope composition of the high-rank taxonomic groups reflects differences in trophic level and in the use of basal resources. Different taxonomic groups of predators and decomposers are likely linked to different pools of organic matter in soil, suggesting different functional roles and indicating that trophic niches in soil animal communities are phylogenetically structured. During last two decades studies using stable isotope analysis have elucidated the trophic structure of soil communities, clarified basal food resources of the soil food web and revealed links between above- and belowground ecosystem compartments. Extending the use of stable isotope analysis to a wider range of soil-dwelling organisms, including mi...

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Section: Trophic Niche Metricsmentioning

confidence: 95%

Section: Baseline Normalization Across Ecosystemsmentioning

confidence: 97%

Section: Trophic Enrichmentmentioning

confidence: 99%

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Uncovering trophic positions and food resources of soil animals using bulk natural stable isotope composition

2018

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“…Soil food webs are characterised by two distinct resources, living plant roots and detritus (De Ruiter et al, 1993), with the majority of soil groups consuming from the detrital food web (Korobushkin, Gongalsky & Tiunov, 2014). The δ 15 N of non-plant feeders, namely, saprophagous omnivores, bacterial feeders and fungal feeders, in soil food webs are elevated through the assimilation of microbially-processed organic matter with a marked isotopic distance from plant matter (Hendrix et al, 1999).…”

Section: Discussionmentioning

confidence: 99%

“…More information is becoming available on trophic distances between feeding groups in soil food webs, as evinced by a recent stable isotope meta-analysis (Korobushkin, Gongalsky & Tiunov, 2014). , However, the ‘trophic distance’ in soils is less clear than between trophic levels (i.e., 3.4 mUr for δ 15 N) in other systems (Hendrix et al, 1999), with soil food webs having more trophic levels than other food webs (Digel et al, 2014).…”

Section: Discussionmentioning

confidence: 99%

Stable isotope analysis (δ¹³C andδ¹⁵N) of soil nematodes from four feeding groups

Melody

Griffiths

Dyckmans

et al. 2016

PeerJ

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Soil nematode feeding groups are a long-established trophic categorisation largely based on morphology and are used in ecological indices to monitor and analyse the biological state of soils. Stable isotope ratio analysis (13C/12C and 15N/14N, expressed as δ13C and δ15N) has provided verification of, and novel insights into, the feeding ecology of soil animals such as earthworms and mites. However, isotopic studies of soil nematodes have been limited to date as conventional stable isotope ratio analysis needs impractically large numbers of nematodes (up to 1,000) to achieve required minimum sample weights (typically >100 µg C and N). Here, micro-sample near-conventional elemental analysis–isotopic ratio mass spectrometry (μEA–IRMS) of C and N using microgram samples (typically 20 µg dry weight), was employed to compare the trophic position of selected soil nematode taxa from four feeding groups: predators (Anatonchus and Mononchus), bacterial feeders (Plectus and Rhabditis), omnivores (Aporcelaimidae and Qudsianematidae) and plant feeder (Rotylenchus). Free-living nematodes were collected from conventionally and organically managed arable soils. As few as 15 nematodes, for omnivores and predators, were sufficient to reach the 20 µg dry weight target. There was no significant difference in δ15N (p = 0.290) or δ13C (p = 0.706) between conventional and organic agronomic treatments but, within treatments, there was a significant difference in N and C stable isotope ratios between the plant feeder, Rotylenchus (δ15N = 1.08 to 3.22 mUr‰, δ13C = –29.58 to –27.87 mUr) and all other groups. There was an average difference of 9.62 mUr in δ15N between the plant feeder and the predator group (δ15N = 9.89 to 12.79 mUr, δ13C = –27.04 to –25.51 mUr). Isotopic niche widths were calculated as Bayesian derived standard ellipse areas and were smallest for the plant feeder (1.37 mUr2) and the predators (1.73 mUr2), but largest for omnivores (3.83 mUr2). These data may reflect more preferential feeding by the plant feeder and predators, as assumed by classical morphology-based feeding groups, and indicate that omnivory may be more widespread across detritivore groups i.e. bacterial feeders (3.81 mUr2). Trophic information for soil nematodes derived from stable isotope analysis, scaled as finely as species level in some cases, will complement existing indices for soil biological assessment and monitoring, and can potentially be used to identify new trophic interactions in soils. The isotopic technique used here, to compare nematode feeding group members largely confirm their trophic relations based on morphological studies.

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Widespread variation in stable isotope trophic position estimates: patterns, causes, and potential consequences

Kjeldgaard

Hewlett

Eubanks

2021

Ecological Monographs

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Stable isotope analysis is one of the most widely used techniques to estimate trophic position and provides fundamental insight into the structure and management of ecological communities. To account for the effects of geographic variation in isotope levels, trophic position is typically estimated relative to an isotope “baseline” (i.e., material representing geographic variation) using a methodology such as a formula or statistical analysis. There is, however, remarkable variation in the baselines and methodologies used to estimate trophic position from stable isotopes. The consequences of this lack of standardization are unknown but could result in biased or erroneous conclusions. We conducted a literature review to quantify the variation in baselines and methodologies used to estimate trophic position from stable isotopes. Next, we assessed the consequences of this variation on individual species estimates and food web structure by extracting published trophic positions and applying various baselines and methodologies to existing data sets. We identified 10 baselines and eight methodologies, the use of which varied by ecosystem studied. Moreover, we found that different baselines and methodologies yield significantly different trophic position estimates for individual species, as well as different conclusions about food web structure. Authors should avoid biological interpretations of absolute, stand‐alone trophic positions (as these are prone to a number of biases). We recommend pairing stable isotope analysis with other techniques for more robust conclusions. Increased sample size may mitigate some of the variation caused by different baselines and methodologies; however, an alarmingly large proportion of studies collected only one sample in at least one trophic group (41% of all reviewed studies). Authors should collect a minimum of five samples per trophic group (but ten for best practices) from as many trophic groups as possible to increase statistical power and redundancy in comparisons. When sample size is unavoidably constrained, we recommend using compound‐specific isotope analysis with a taxon‐specific trophic discrimination factor, because it may be more accurate and require fewer samples to maintain appropriate statistical power. Implementing our recommendations will increase the robustness and accuracy of conclusions based on stable isotopes, resulting in better management decisions and a more accurate understanding of ecological communities.

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Isotopic niche (δ¹³С and δ¹⁵N values) of soil macrofauna in temperate forests

Cited by 38 publications

References 56 publications

Uncovering trophic positions and food resources of soil animals using bulk natural stable isotope composition

Uncovering trophic positions and food resources of soil animals using bulk natural stable isotope composition

Stable isotope analysis (δ¹³C andδ¹⁵N) of soil nematodes from four feeding groups

Widespread variation in stable isotope trophic position estimates: patterns, causes, and potential consequences

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Isotopic niche (δ13С and δ15N values) of soil macrofauna in temperate forests

Cited by 38 publications

References 56 publications

Uncovering trophic positions and food resources of soil animals using bulk natural stable isotope composition

Uncovering trophic positions and food resources of soil animals using bulk natural stable isotope composition

Stable isotope analysis (δ13C andδ15N) of soil nematodes from four feeding groups

Widespread variation in stable isotope trophic position estimates: patterns, causes, and potential consequences

Contact Info

Product

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Isotopic niche (δ¹³С and δ¹⁵N values) of soil macrofauna in temperate forests

Stable isotope analysis (δ¹³C andδ¹⁵N) of soil nematodes from four feeding groups