Analysis of trophic structure

Sample collection

For each taxonomic group or solid type of organic material enough dry matter must be collected to amount to minimum 1 mg or approx. 300 µg per triplicate.

A sample should contain between 20-150 µg N and 200-2000 µg C [1]:

To determine the amount of organic material use the Sample Weight Calculator to determine the amount of material accepted by SIF.

Sample preparation

All material for isotope analysis is dried at 60 ^oC (may depend on type of material) for maximum 24 h or until constant weight which may occur after only 3 hours.

• Each sample of microarthropods typically consists of pooled individuals (e.g. between 1 and 120 adult specimens based on body size of the species) to obtain sufficient material for ¹⁵N/¹³C analysis.
• Soil: a representative sample of the soil sieved through 2 mm mesh is used to indicate the isotope ratios for total soil organic matter. All visible non-soil organic matter is cleaned from the soil including, roots, plant remains. Details of the procedure is discussed with the project manager before implementation.
• Roots: a representative sample of roots is collected from the foerne samples. If roots has clearly vivible differences that can be grouped, then they should possible be kept separate. Details of the procedure is discussed with the project manager before implementation.
• Shoots: dominating above-ground plant material including senescent leaves are collected from the foerne samples. Any vivible types of plant material is considered for separation into different plant material types.

The dried samples may be grinded or otherwise crushed to ensure homogenrity and representativity of the whole sample.
One replicate tin capsules consisting of pooled animals
from the same habitat and treatment will be analysed for stable isotopes. However a few
samples will be analysed in duplicate and triplicate, to assess the within-sample variability.

For details on sample preparation in tin capsules and collection into 96-well microplates read SIF guidelines or the pdf version here.

Soluble organic compound and microbial biomass: possible extraction with chloroform-fumigation (Coyle et al. 2009) may be considered in

future studies.

Sample analysis        

 The tin capsules with material for analysis are send to:

UC Davis Stable Isotope Facility (SIF)
Department of Plant Sciences
California

web address: stableisotopefacility.ucdavis.edu

An order form and a sample list is filled and e-mailed to: sif@ucdavis.edu. Printout is included with the sample package.

Calculations

Stable isotope abundances of ¹³C and ¹⁵N are expressed using the δ notation in parts per thousand:
δ X (‰) = (R_sample/R_standard - 1) 1000
where X= ¹³C or ¹⁵N and R is ¹³C/¹²C or ¹⁵N/¹⁴N.