Soils, including litter layers, provide a habitat for a wide range of soil organisms. Organisms that are visible to the naked eye, but which can fit through a 2mm hole are called “mesofauna”, smaller animals are micro-organisms (needing a microscope to view), and larger ones are macro-fauna. Soil mesofauna are the most abundant visible organisms in most terrestrial ecosystems, and are dominated by mites, springtails, insects, other hexapods and smaller oligochaete worms. The types numbers and diversity of soil mesofauna indicate soil processes. Mesofauna biomass reflects the amount of organic matter entering the soil, and provides an overall indicator of rates of soil function, the types of organisms present indicate the rates of nutrient turnover (how fast nutrients are released from organic matter), and levels of disturbance. A more detailed understanding of soil mesofauna communities can reflect many other soil properties, such as pH and moisture regime. In this activity, participants will collect soil samples, extract soil mesofauna and interpret the results. Students will collect a known volume of soil, and extract soil mesofauna using a Tullgren Funnel apparatus, which takes advantage of the natural behaviour of most soil animals to avoid excessing heat, light and dryness, to drive specimens into a collecting pot.
- Understand that soils are homes to a wide diversity of living organisms
- Understand how to sample for, and extract, soil mesofauna.
- (Context dependent extension) appreciate how energy supply and disturbance affect soil communities.
- Identify and classify soil mesofauna using a simple key
- (Extension) use published keys and compound microscopes to identify specimens to higher taxonomic levels.
- 4 cm diameter plastic drainage pipe cut into 8 cm lengths (1 per sample)
- Nylon netting
- Rubber bands
- PVC tape
- Long-bladed knife with protective sheath.
- Wooden block
- Ziplock bags
- Marker pen
- GPS (optional)
- Posable desk/bedside lamp with 40W incandescent bulb (one per sample is ideal, can 1 between 2 samples)
- Plastic funnel (one per sample).
- 5cm diameter petri dishes.
- Gardening gloves
- Metal mesh with 2mm holes (availanle from car supplies)
- Pint glasses
- Collection pots (50ml centrifuge tube or similar is ideal)
- Microscope (USB or binocular dissecting microscope with top lighting)
- Printed keys (see appendix).
- Compound microscopes for extension (more detailed identification)
Net-capped plastic cores can be prepared in advance. Cut a 10cm by 10cm square of netting, secure over one end of the 8cm long pipe using a rubber band, trim off excess netting around the rubber band, secure netting beneath rubber band with PVC tape, remove rubber band, and continue to secure netting with PVC tape around sides of tube, leave top open.
Allow 10 minutes for sampling in the field in each location and factor in any travel time to, from and between sites. Allow 20 minutes for setting up Tullgren funnels. Allow 3-5 days for full extraction of soil mesofauna. For reasonably dry soils, a large proportion of the community can be extracted from 1 overnight extraction. Allow half an hour for superficial examination of the extracted organisms. Extension: full identification of soil organisms from a single sample would take an expert several days!
|Disease from soil||Low||High||Ensure participants have Tetanus jabs, wear gloves if there are cuts on hands, advise participants to avoid contact between hands and mouth, eyes, nose etc.|
|Injury from knives and plastic cores (sharp edges)||High||Low||Advise participants to cut away from themselves, and to wear protective (gardening) gloves to avoid small cuts. Keep knives in sheaths when not in use.|
|Alcohol – risk of poisoning and/or fire||Low||Medium/high||Ensure participants can be trusted to behave responsibly advised not to drink alcohol, clean up spills immediately, do not allow smoking or other naked flames near alcohol. Ensure that Tullgren funnels and microscopic examination of extracts are set up in adequately ventilated areas to avoid headaches etc.|
|Eye strain, muscle strain from working at microscopes.||Medium||low||Encourage participants to take regular breaks and encourage them to establish a comfortable working position providing adjustable chairs and/or different height benches etc.|
|Site/local specific risks||Unknown||Unknown||Anyone running this activity should consider risks particular to their location, trainees and circumstances and develop suitable mitigation strategies.|
Description of activities
- Pick areas of soil to sample. It is suggested that you compare at least two areas of soil which differ strongly in their i) vegetation type ii) amount of plant cover iii) history of management iv) time since last disturbance.
- Place a tube, gauze side up, onto the surface of the area to be sampled on top of the vegetation/litter. Press down onto the soil surface and do not remove – some soil bugs will jump away!
- Unsheath the knife and carefully cut vertically around the tube’s base.
- Use the mallet and block to drive the core into the soil so that the gauze is level with the surrounding soil surface.
- Use the knife to cut out a triangular wedge next to the tube, and lever out with a trowel.
- Push the tip of the trowel under the bottom of the tube (cut through any roots with a knife if needed), and carefully lift out the tube.
- Trim excess soil off the bottom of the tube using the knife or scissors.
- Wrap the tube in clingfilm and place into a labelled sample bag (name, date, location, treatment/vegetation)
- Optional – use a GPS to record the location of the sample – this is useful for accurate recording of the species and communities found.
- Indoors, put approximately 15 ml of 70% industrial methylated spirits into a 50ml container.
- Place this container carefully at the bottom of a pint glass
- Place the funnel into the pint glass so that the tip of the funnel is inside the mouth of the 50ml container, but above the level of the methylated spirits.
- Line the funnel with a sheet of metal mesh with 2mm holes, pressing it around the edges so that there are no gaps
- Carefully remove the net cap from the soil sample and gently push out the soil core, laying it on its side on the mesh. You may need to remove the funnel temporarily from the glass to do this, and use 2 people to complete this task, before replacing the funnel over the container in the glass.
- Place the desk lamp on a higher surface and angle it downwards so that the bulb is 2-3cm from the soil. You may need to angle the lap sideways to avoid the base interfering with the funnel and switch the lamp on.
- Leave for 5 days (maximum) or overnight (minimum). Please note that for full extraction of all organisms, the soil should be completely dry by the end of the process.
- Carefully remove the funnel and dry soil and place to one side.
- Remove the 50ml collection pot, gently swirl the contents and pour into a 5cm petri dish.
- Place the petri dish under a microscope (binocular or USB).
- Compare the numbers, sizes, and types of organisms – are they large and pale/coloured, or smaller and dark/hardened? How many organisms have emerged and how does this relate to past management?
A simple pictorial key is provided at the end of this document, copied from Wheater & Read 1996. Pictures of different soil samples have been provided to help you interpret the results.
Few organisms indicate that there is little organic matter available to support the soil fauna, or help fuel soil functions and processes. Discuss: what are the soil processes that need energy (answers: soil structure formation, plant nutrient release).
Many small, round very dark organisms (see Permanent Grassland below): these are oribatid mites, which are decomposers, and are more abundant where the organic matter is lower in nutrients. They live longer (3-4 years), grow slowly, and must protect themselves (their dark colour is due to their hard, sclerotised, armoured exoskeleton).
Mostly larger, pale organisms (see Herb-rich ley below): these tend to indicate rapid nutrient turnover: rapid growth of plants, which have high nutrient contents and decompose rapidly, to release nutrients rapidly. The soil organisms grow larger, more quickly, reflecting an abundance of nutrient-rich food supply.
Few small white organisms (see Compacted arable below): these may be relatives of dust mites (hairy!) and indicate disturbed habitats with little available food, or dry conditions. These animals disperse easily (their nymphs ride on insects) and breed rapidly, to use up temporarily available food supplies.
For more detailed keys see: Springtails http://www.field-studies-council.org/publications/pubs/a-key-to-the-collembola-(springtails)-of-britain-and-ireland.aspx or http://www.field-studies-council.org/publications/pubs/illustrated-key-to-the-families-of-british-springtails-(collembola).aspx ; Mites https://www.dropbox.com/s/udzr5huqyhtpzr2/Mites%20Key%20Test%205f.pdf?dl=0 ; other soil organisms http://www.field-studies-council.org/publications/pubs/a-key-to-the-major-groups-of-terrestrial-invertebrates.aspx ; woodland mini-beasts http://www.field-studies-council.org/publications/pubs/woodland-name-trail-(mini-beasts).aspx