Do One Thing

Summer Term 2009

Playing fields and sports grounds aren't just for sport, they can also be a great place for science investigations. And summer is the perfect time to do science out of doors. This page contains ideas for projects on plants that you should be able to carry out in your local area.

In a single grassy field, some parts of the field will be damper than others. The amount of water in the soil is very variable. These damp areas are different habitats for plants than dry areas. This is because an environment factor (soil water) is different between the two places. You could investigate the variations in soil moisture in different parts of the field.

If you have made a bog garden, you could investigate how the plants in the bog garden are different to those growing in drier soil elsewhere. Late spring and early summer, when many of these plants will be in flower, is the best time of year to carry out an investigation. Here are some photographs of a pond and bog garden.

	A bog garden has been created at the edge of this small pond. The ground slopes gently upwards from the edge of the water. Soil close to the water is very wet, but it becomes drier the further up the slope. At the edge of the pond garden there is a small area of grassland.
	This is a different view of the same pond. Some plants are only found in the wettest ground (e.g. marsh marigold - the plant with yellow flowers), some are found in slightly drier ground (e.g. water mint and soft rush, both in the centre of the photo) while others grow only in drier soils.
	In this grassy area in Finsbury Park in London, soil on the left is much damper than soil on the right. There is also a small slope in the background - you could compare plants growing on the top, middle and base of the slope.

How does water in the soil affect plants?

Plants use water in photosynthesis, to transport minerals and to make the plant firm. Water in the soil can be a problem for plants if there is too little water or too much water. To understand why this happens, we need to remember what happens in the processes of photosynthesis and respiration.

In the process of photosythesis, plants use carbon dioxide from the air and water taken in through the roots to make carbohydrates.

In the process of respiration, cells within the plant use carbohydrates made in photosynthesis and oxygen taken in from the air to release energy.

If there is too little water in the soil, the leaves can wilt. Wilting is a way in which the plant tries to save the water which it already has. Unfortunately, a plant with wilted leaves will photosynthesise at a lower rate than plants without wilted leaves. A wilted leaf the is no longer held at a right angle to the sun, so is much less efficient at catching light.

If there is too much water in the soil, there will be less oxygen in the soil around the roots. Instead of being filled with air (which contains oxygen), gaps in the soil are filled with water. Roots, like any part of the plant, need oxygen for respiration.

Which plants grow where?

Bog garden plants

Plants which grow in soil with a high moisture content (like a bog garden) have special adaptations to overcome the lack of oxygen in the soil. Here are some examples.

Marsh marigold	Soft rush
Ragged robin	Water mint

The roots and stems of soft rush are spongy because they contain with air spaces. These air spaces allows oxygen to pass to the roots for use in respiration. Marsh marigold is tolerant of soils with a high moisture content. Ragged robin and water mint and will be found in slightly drier soil, higher up in the bog garden, and other damp places like the bottom of wet grassy ditches.

Damp grassland plants

There is not a sudden break from bog garden to damp grassland. Plants like ragged robin and water mint will continue to be found, but they will be joined by other like cuckoo flower and slender speedwell.

The three most common species of buttercups are found growing in different places. If you study a slope (like the edge of a ditch) in May and June, you might see that creeping buttercup is commonest at the bottom of the slope, meadow buttercup is commoner in the middle of the slope and bulbous buttercup is found at the top of the slope. You can download a simple key (with photographs) to these buttercups from the SAPS website (pdf).

Creeping buttercup	Meadow buttercup
Daisy	Cuckoo flower
Slender speedwell	Moss

Dry grassland plants

Among the grass, you should find plants which are not tolerant of high soil moisture content. Slender speedwell is replaced by Germander speedwell, and bulbous butterup is found at the top of slopes.

Germander speedwell	Bulbous buttercup
Common mouse-ear	Hop trefoil

Investigating plants and soil moisture

There are many possible scientific investigations that you can carry out to test the effect of soil moisture on plants.

1. Density of one species in two habitats

The simplest investigation is to concentrate on one species of plant and see if there is a difference in the amount of that plant in wet and dry areas. For example:
Are there more daisies in wet parts of the field than in dry parts of the field?

To answer this question, choose two parts of the field where there is a difference in soil moisture. Make sure that it is a fair test, and that you have controlled other variables such as the amount of trampling. Use random sampling to place at least 10 quadrats in each part of the field. Count the number of daisy plants in each quadrat. Find the average number of daisies per quadrat in each part of the field. Is there a difference?

For more detail on how to carry out this investigation, see KS3 Science: Where do most daisies grow?

2. Percentage cover in two habitats

You can carry out other investigations into one type of plant, such as Is there more moss in wet parts of the field than in dry parts of the field?

For some plants (like grass and moss) it is difficult to work out where each plant begins and ends. Instead of counting the number of individual plants in a quadrat, estimate what percentage of the quadrat is covered by each species of plant. You might estimate, for example, that moss covers a quarter of the ground surface, so record 25% moss. This is easier to do if you are using a gridded quadrat which is divided into 100 squares. You can either concentrate on recording the percentage cover of a small number of species or try to record the percentage cover of all species.

3. Wet-dry transect with a small number of species

A more difficult investigation is to set up a transect. This can work well if there if, for example, the bog garden is gently sloping or it has been created on the edge of a grassy field.

Instead of random sampling, you need to take measurements along a transect - a line running along the environmental gradient from soil with a high moisture content to soil with a low moisture content. Use a tape measure or piece of string to mark a straight line 20m across the area you are investigating.

Concentrate on three species of plant that you suspect show a change along the transect. You may wish to concentrate on the three species of buttercup shown above (creeping buttercup, meadow buttercup and bulbous buttercup). Or you can choose one bog garden plant, one damp grassland plant and one dry grassland plant. Place a quadrat at one end of the transect. Count how many plants of your chosen species there are in the quadrat. Measure a metre along the string from the edge of your quadrat. Again count the number of plants. Carry on doing this until you have completed results for 10 quadrats.

You can display your results on a bar charts. Drawing the bar charts on the same sheet of graph paper will allow you to compare the species easily.

4. Wet-dry transect with percentage cover

This is similar to 3. Instead of random sampling, you need to take measurements along a transect - a line running along the environmental gradient from soil with a high moisture content to soil with a low moisture content. Use a tape measure or piece of string to mark a straight line 20m across the area you are investigating.

Place a quadrat at one end of the transect. Try to measure what percentage of the quadrat is covered by each species of plant. You might estimate, for example, that moss covers a quarter of the ground surface, so record 25% moss. This is easier to do if you are using a gridded quadrat which is divided into 100 squares. You can either concentrate on recording the percentage cover of a small number of species or try to record the percentage cover of all species.

5. Full investigation

As well as carrying out a wet-dry transect with percentage cover, for a full investigation you should try to measure some of the environmental factors as well. Soil moisture levels are the most important environmental factors. Use a trowel to dig a small amount of soil from the centre of each quadrat. You can quickly estimate soil moisture by taking a handful of soil in the plam of your hand and squeeze it. How wet is the soil?

• Dry - soil is loose and does not stick together when squeezed
• Moist - soil sticks together but water does not drip out when squeezed
• Wet - soil sticks together and water drips out when squeezed.

Other environmental factors that you may want to measure include soil pH, soil hardness and light levels. There is more information on how to measure these things at the Urban Ecosystems website.

More information

The Urban Ecosystems website has sections on grassland and wasteland.

The Life in Freshwater website has background material on ponds and rivers.

For more help with identifying common grassland plants, see the Playing field plants chart.