DOI: 10.5061/dryad.mcvdnck3m
title: Channelling of basal resources and use of allochthonous marine carbon by soil arthropods of the Wadden Sea salt marsh

description: Salt marshes are located between the marine and terrestrial systems.
 Because they form as sediment accumulates, they comprise a gradient of
 shore height with differing inundation frequencies and associated abiotic
 soil conditions. Along this gradient, both autochthonous vascular plant
 resources and allochthonous marine algal or detrital resources are
 available, with the availability of both varying with season and salt
 marsh zone. However, little is known about the importance of either
 resource for the soil animal food web. We investigated both spatial and
 temporal resource use of the soil macro- and mesofauna of the salt marsh
 using neutral lipid fatty acids (NLFAs). Generally, irrespective of season
 and zone the soil animal food web relied on carbon originating from
 autochthonous vascular plants and associated bacteria and fungi, with the
 role of bacteria generally exceeding that of fungi. However, the
 channelling of fungal resources consistently peaked in October, whereas
 seasonal changes in the channelling of plant and bacterial resources
 varied among salt marsh zones. Further, variations in the channelling of
 resources with season and zone varied among salt marsh animal species.
 Although being only minor, allochthonous resources of marine origin
 contributed to soil food web nutrition across salt marsh zones and
 seasons. The contribution of algae to soil food web nutrition depended on
 inundation frequency and season, i.e. algal productivity. Overall, the
 results demonstrate that the salt marsh soil fauna predominantly relies on
 autochthonous vascular plant resources, with the contribution of
 allochthonous marine resources being minor and restricted to few taxa.
description: Samples were taken along five transects spanning across the USM,
 LSM and PZ on the island of Spiekeroog (Wadden Sea National Park, Germany;
 53˚45’2”- 53˚47’1”N, 7˚40’0”-7˚49’1”E) in April (spring), July (summer)
 and October (autumn) 2019. Within each transect, one soil core of 20 cm
 diameter was taken per zone and separated into two layers (0–5 and 5–10 cm
 depth). Cores were stored in plastic containers and kept at ambient
 temperature until soil fauna extraction at the University of Göttingen.
 Soil fauna was extracted using heat (Kempson et al. 1963); animals were
 extracted into a 1:1 mixture of Glycol and water. Once extracted, the
 animals were filtered through 45 µm gauze, flushed with water and placed
 into 70 % ethanol for storage at -20°C. Animals were identified under a
 stereomicroscope, macrofauna was identified to species, whereas mesofauna
 species were grouped to higher taxonomic units to gain sufficient material
 for lipid extraction. To achieve sufficient fauna material soil horizons
 and samples were in part pooled. The identification followed (Weigmann
 2006), and (Schaefer 2018). Sorting was done within 2–4 weeks after
 extraction to minimize the loss of lipids due to placement in ethanol;
 prior to storage the ethanol was evaporated and the animals placed at
 -20°C. Lipid extraction and allocation:
 Animals were placed into 10 mL tubes and extracted as described
 in Haubert et al. (2004). In brief, animals were shaken in 5 ml extraction
 solution [chloroform/methanol/0.05 M phosphate buffer (pH 7.4), 1:2:0.8]
 overnight. Then, the extract was transferred to fresh tubes with
 additional 2.5 ml extraction solution and shaken for 1 h. Chloroform and
 distilled water were added (0.8 ml each), vortexed and centrifuged at 1500
 rpm at 7–10 °C for 5 min. The top phase was removed, and the remaining
 phase was fractionated in silica columns (Chromabond® SiOH (3 ml),
 Machery-Nagel™, Düren, Germany) and eluted with 1.5 ml then 2 ml
 chloroform. Samples were then dried at 30 °C in a vacuum centrifuge before
 saponification with 1 ml of a sodium hydroxide–methanol solution (45 g
 NaOH, 150 ml CH<sub>3</sub>OH, 150 ml distilled
 H<sub>2</sub>O) at 100°C for 30 min. Followed by methylation
 with 2 ml HCl – methanol solution (325 ml 6.0 N HCl, 275 ml
 CH<sub>3</sub>OH) at 80°C for 10 min. Finally, neutral lipids
 were extracted into hexane – methyl tertiary butyl ether (1:1) and washed
 with liquid NaOH (10.8 g NaOH, 900 ml distilled
 H<sub>2</sub>O). Lipids were stored in 1.5 ml GC-vials, capped
 and stored at -20°C until gas chromatography. Lipids
 were separated using a gas chromatograph (Clarus 500, PerkinElmer
 Corporation, Norwalk, USA) equipped with an Elite-5 capillary column (30 m
 x 0.32 mm i.d., film thickness 0.25 mm, PerkinElmer, Norwalk, USA). The
 analysis started with 60°C for 1 min, increased by 30°C/min to 160°C;
 followed by 3°C/min increase to 260°C; injection temperature was 250°C,
 with helium as carrier gas. Lipids were identified by retention time,
 based on standard mixtures composed of 37 FAMEs (Fatty Acid Methyl Esters)
 ranging between chain lengths of C11-C24, as well as 26 BAMEs (Bacterial
 Acid Methyl Esters, Sigma-Aldrich, St Louis, USA) and algal standards for
 16:2ω6,9 and 16:3ω3,6,9 (Larodan AB, Solna, Sweden) (Buse et al. 2013).
 Lipid concentration was calculated as percentages Only lipids contributing
 &gt;1 % of total were included in the analysis. Lipids were aggregated
 into six NLFA marker groups including algae (14:0; 16:2ω6,9; 16:3ω3,6,9
 and 20:5ω3,6,9,12,15), animals (20:1ω9), bacteria (a15:0; i15:0; i16:0;
 16:1ω7; i17:0 and 18:1ω7), fungi (18:2ω6,9), vascular plants (18:1ω9 and
 24:0) and unspecific (13:0, 14:1, 15:0, 16:0, 17:0, 17:1, 18:0, 20:0,
 20:2, 20:3ω6,9,12, 20:4ω6,9,12,15). All values given in
 data table are percentages % (see above).
description: Program required: Microsoft Excel, or similar