Microarthropod sampling

Principle:

Soil microarthropods flee a heating soil sample, falling into a collection vessel, where they can be counted under a microscope.

Notes:

Before sampling, set up the laboratory apparatus, since you should process your soil samples as soon as possible after you collect them. The longer you delay, more microarthropods will die or not respond to the extraction and you will end up with fewer.

Equipment:

  • Tullgren extractor setups, one for each soil sample (you will get these from the biology department; they have 12)(Fig. 1)
    • Ring stand
    • Funnel
    • Screen
    • Light source
    • Sample jars with 70% ethanol to catch the microarthropods
  • Dissecting microscope
  • Petri plates and a dissecting needle for sorting and counting organisms
  • Ziplock bags, sharpie, and cooler for collecting samples from the field
  • Soil corer, at least 5 cm diameter, preferably one with an internal sleeve
  • Field notebook for recording data

Procedure:

  1. In the lab, make sure your Tullgren funnels are clean, dry, and ready to go except for the ethanol collector jars.
  2. Collect soil samples using a 5-10 cm corer. If possible, use a piston corer with an internal sample sleeve of known volume. Get at least the top 5-10 cm of soil. If sampling from grassland soils with a deep A horizon, you may need to sample to 15 cm depth. However you collect the samples, be consistent between sample sites and record your sampling method in your field notebook.
  3. Each sample (bare soil or a sample sleeve containing soil) should be placed immediately in a ziplock bag, labeled with date, sample site, treatment (e.g. soil type) and the initials of the investigator, and placed into the cooler for transport back to the laboratory.
  4. In the lab, label a jar of ethanol solution with a sharpie and put it underneth a Tullgren funnel, then empty the contents of the corresponding bag onto the screen. If you used a corer with inner sleeves, the entire sleeve can be placed inverted (original soil surface down) atop the screen. Repeat for each sample.
  5. Turn on the lights and allow the extractions to continue for one week. During this time, look in periodically to make sure the light bulbs are working and the ethanol is not evaporating.
  6. Sort and count microarthropods for each sample. A preliminary level of detail is quanitifying collembolans, mites, and all other microarthropods. This can be done with a dissecting scope between 10x and 40x magnification.
    1. Transfer the contents of a sample jar to a petri dish for sorting and counting.
    2. Use the dissecting needle to transfer individual microarthropods to other labeled containers with a small amount of 70% ethanol in each. Don't stab them with the needle, you can just "scoop" them up and they should cling to the needle.
  7. The identification of microarthropods to the species level requires a high-magnification microscope, probably a phase contrast microscope, and additional procedures to clear and mount each specimen.
Tullgren funnel
Figure 1: Tullgren funnel setup.  (a) Sample cover; (b) sample; (c) screen; (d) funnel; (e) collection vessel.  Figure from Coleman, D.C., A.D. Crossley Jr., and P.F. Hendrix, 2004. Fundamentals of Soil Ecology 2e. Burlington, MA: Elsevier Academic Press.

Tullgren funnels in use
Figure 2: Tullgren funnels in use.

Figure 3: Identifying microarthropods
Comments