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Collecting samples to analyse in the laboratory

During your visit to the Sainsbury Laboratory you will be analysing samples of bacteria extracted from the root nodules of white clover.

Why

We want to explore the genetic diversity of bacteria that form a symbiotic relationship with white clover growing in different areas of the UK.

How you can help

If you are registered to attend our Cambridge Festival event on Sunday 3 April 2022 and also register to collect your own samples, please watch the video on this page and read the below instructions on collecting clover samples. We will send registered participants a collection kit together with a self-addressed and stamped return envelope. Please do not send us samples unless you have registered to be a collector and a collection kit is sent to you.

All samples must be posted back to us by St Patrick's Day (17 March 2022) so they arrive in time to be ready for our event. 

Thank you for participating in this project with us. We look forward to welcoming you to the Lab to learn more about your samples!

 

What is white clover

  

White clover (Trifolium repens) in flower. Image credit: Forest & Kim Starr, CC BY 3.0, via Wikimedia Commons

 

White clover (Trifolium repens) is a small herbaceous (non-woody) perennial that is native to Europe, including the UK, and central Asia. It is the most widely cultivated clover in the world and is grown in mixed pastures for animal forage. As a result of its domestication and its voracious ability to spread through stolons (horizontal stems that form roots) it has spread throughout the world and is often considered a weed in gardens, lawns and arable crops. 

However, white clover is valuable to pollinators. It produces abundant nectar that honey bees and short-tongued bumblebees and solitary bees love.

White clover is a valuable nectar source for bees. Image credit: Andy Murray, CC BY-SA 2.0, via Wikimedia Commons

 

Other plants also benefit as it replenishes the soil with nitrogen thanks to a special partnership it has formed with soil bacteria. White clover is a legume, which is in the same family as beans and peas. Many legumes, including white clover, host soil bacteria in their roots in roundish structures called root nodules. These bacteria convert nitrogen from the air into a form that the host plant can use – this process is called nitrogen fixation. And this is the process that we are interested in exploring in this project.

How to identify white clover

  

White clover is very low growing (like a carpet) and at this time of the year you will possibly only see leaves as it is too early for flowers (it usually flowers June to September). The leaves are quite a distinct clover-shape – called a compound leaf, with three rounded leaflets. One of the key distinguishing features of clover is the white band across the middle of the leaflets which is often a chevron shape. 

White clover growing on a mowed patch of lawn.


Close-up images of white clover compound leaves, showing distinguishing white chevron-shaped marking across the leaflets.

Look-alike plants

  

Some other plants you might find look similar to white clover. We have listed below some common look-alikes with photos to help you distinguish between them: 

Red or Crimson Clover (various species): This has significantly larger and more elongated leaves that have a tapering/narrow tip compared to the rounded white clover leaflets. It also usually has the white chevron-shaped band across each leaflet. The leaflets have tiny but visible hairs on both sides.

Crimson clover in field (left) and compared with white clover (right) to illustrate crimson clover's larger and more elgongated leaflets with tapering tip.

 

Trefoils and Medicks (various species): Trefoils and medicks are also legumes. Their leaves are very similar to white clover, especially early in spring. It can be very difficult to tell them apart without the flowers. The leaves can be heart-shaped or quite narrow and the edges of leaflets also have notches (to make the heart) or are serrated. Both trefoils and medicks commonly occur in disturbed bare ground, bases of walls and pavement cracks.

 Spotted medick (left), birdsfoot trefoil (middle) and black medick (right).

 

Oxalis (various species): The leaves look very similar to clover, but it is usually taller with the leaves occurring only at the tip of a fleshy upright stem and occurs in quite prominent clumps. The leaflets come in many sizes and are often heart shaped, some with a deep notch, or are almost a triangle shape.

Creeping wood sorrel (left) and unidentified oxalis species in grassy verges in England.

 

Columbine: The early spring leaves of columbine look similar to clover leaves, but are significantly larger and have wavy edges and usually have a blueish tinge. 

Examples of seedlings of columbine (Aquilegia).

 

Creeping Buttercup: Creeping butter cup has deeply serrated leaflet but can sometimes look a bit like clover hiding amongst grass. 

Creeping buttercup has deeply serrated leaflets. You might be able to spot some tiny white clover leaflets among the grass and buttercup leaves in the far right image.

 

Silverweed and other Rosaceae species: Common in lawns, In the early stages of growth the new leaves might look a little bit like the white clover compound leaf. They leaflet edges are serrated. 

Silverleaf and other creeping plants in the Rosaceae family are commonly found in lawns.

Where to find

Search for white clover in your own garden, allotment, or somewhere where you have the landowner’s permission to uproot plants, for example you could ask your school for permission. For more guidelines on plant collection, read the Botanical Society of Britain and Ireland (BSBI) Code of Conduct. Please ensure you are collecting somewhere safe and stay aware of your surroundings.

Once you have found some white clover plants, take a photo of the clover you are about to harvest and record the location using your phone’s GPS coordinates, What3Words, a screenshot of your map location, or record via another method. If you are unsure of whether you have found the right plant, email us a photo at events@slcu.cam.ac.uk before collecting.

How to collect

Put on the protective gloves. Have a close look at the plant and find where the stem joins to the soil. Use your trowel or spoon to loosen the soil in an area about 5cm diameter away from the stem. You do not need to dig too deep – about 10cm is adequate. Try to remove the plant with as much root material as possible. Gently shake and tap off the soil to make sure there are roots attached. If the soil is wet or claggy, you may need to wait until you wash the soil off the roots to see them. If you can, try to collect three plants to ensure you have enough root material. White clover usually grows in patches, so you should be able to find a few plants to collect in the same area. Put your samples into one of the resealable bags provided. Return the soil that you dug out back into the hole and tap down the area with your foot to flatten the soil as to not leave a hole behind that someone might trip on.

Check that you have root nodules

  

Take your collected plants home and carefully wash the soil off the roots in an old container filled with water. Don’t wash the soil down your sink plug! Examine the cleaned roots for root nodules using the magnifier. They are roundish shapes attached to the roots. These are the structures that hold nitrogen-fixing bacteria!

The nodules will be different sizes depending on how mature they are. And they can sometimes have a pinkish/reddish colour, which indicates that they are functioning nodules where the bacteria are alive and are actively fixing nitrogen for the plants.

The root nodules start off quite small and grow bigger as they mature. Aim to collect as many nodules as possible (~15-20 nodules in total). Keep the whole plant intact so we can confirm the host plant species.

Post your sample to us

Add a few drops of water to the numbered sample jar to dampen the cotton wool and to help prevent the plants from drying out. Place all three plants you collected into the jar, with roots nearest the cotton wool at the bottom. Close the jar securely. Place the jar in the remaining clean plastic bag and seal. Wash your hands after handling the plants. Fill in the online form we have emailed you with the date, location and photo of your clover samples. Then, post the samples back to us as soon as possible in the envelope provided. If you cannot post the samples immediately, store them in a cool place like a garage or in the shade outside until you can post them.

Please post the samples to us by the 17th March.