Lichens in = Coursework

Using lichens in practical coursework

The = following is=20 intended to give you some brief background information about these = fascinating=20 organisms. The aim is to help you arrive at a suitable topic for = investigation.=20 You should seek further detail relevant to your own investigation from=20 textbooks... but be sure to stick to those dealing with = UK=20 lichens.

What are lichens?
Lichens are = actually two=20 organisms - an alga and a fungus living in symbiotic association. They = are=20 therefore eukaryotes. Thus you should expect to find plastids in = the=20 algal component. the ones you may well be = interested in=20 for coursework projects are the chloroplasts. Figure out for = yourself why=20 I suggest this - or email me if = you=20 cannot see the connection. You may also want to find out what benefits = each=20 partner derives from this association..... Note that in a small = number of=20 cases the lichen contains more than one algal species. You may need to = bear this=20 in mind when designing practical investigations! The lichen has a = totally=20 different form to either the alga or the fungus.

What do they look like?
Lichens vary both in = form and=20 colour. In terms of form, lichens may be:-

Crustose. These are the flat crust like lichens = you=20 commonly see on roofs, tree trunks, stone walls etc. In the=20 UK these probably exhibit = the=20 greatest range of colour.=20
Foliose.=20 These are described as 'leaf like'. Essentially this means the outer = edges are=20 not in intimate contact with the substrate. Some foliose lichens are = lobed=20 whereas others are circular (attached by a single central cord). Some = foliose=20 lichens can feel quite leathery.=20
Squamulose. (Think of squamous epithelium) The = appearance=20 of this form is in between the foliose and crustose=20 type. Thin and crust like but often with small thin lobes. Not = leathery.=20
Fruticose. Possessing erect structures-sometimes = finely=20 branched. Fruiting bodies are at the end of these. Some cladonia species have beautiful red tips. =
Gelatinous.=20 It is not expected you will need to concern yourself with these. =

Identifying lichens can be extremely tricky! You should take this = into=20 account when designing your investigation. Aim to avoid having to = identify the=20 exact type and sub-type, whatever you do! Instead look for the grosser=20 differences- e.g. colour, flattened, foliose = etc....
Colour
Lichens=20 range through shades of green, through blue green to yellow, orange and = silvery=20 blue green. If you have studied photosynthesis you may have carried out=20 chromatography of leaf pigments. You may recall the action and = absorption=20 spectra. You may also recall that different pigments are excited at = different=20 wavelengths of light. Is this significant? You may think so when you = have read=20 to the end.

Different=20 coloured lichens on hawthorn trunks on Dunstable Downs, December. =

"How do they grow?"
Generally very slowly! They are = also=20 long lived - some lichens have been dated at 4500 years old! However you = must be=20 aware that man has not always shared my interest in lichens... in some = churches=20 people become almost paranoid about removing lichens from stonework and=20 gravestones. (they are usually the same = people who want=20 to 'remove' bats because they cause 'mess') You should bear in mind = the=20 effects of removal on the validity of your investigation and plan=20 accordingly..=20
Reproduction in lichens can be complicated- both sexual and = non-sexual=20 reproduction occurs. This is probably not something you need to concern = yourself=20 with for your project... unless you really like making things difficult = for=20 yourself. On the other hand, never let it be said I am a killjoy. =
Lichens do=20 not have true roots- they are like mosses and liverworts in this = respect.=20 However whereas the latter two are attached to the substrate by = rhizoids, some=20 lichens are attached by rhizines = based on a=20 bundle of hyphae.

Where do they grow?
Almost everywhere! You will find = no=20 shortage of sites to survey your lichens.
For = instance=20 on roofs....
But note that you may find different ypes on different roof substrates, slopes = etc. Is=20 there an idea here?

As noted above, you will also find them on tree trunks, fences, = posts, brick=20 and stone walls.
Many lichens are quite substrate specific. = You will=20 therefore need to consider characteristics of the surface, for instance: =

Aspect.=20 Vertical? Horizontal?=20
Type=20 of substrate - rough? smooth? porous? gritty? etc...=20
pH of substrate.

You also need to consider environmental = factors, for=20 instance:

Exposed=20 to wind/rain etc.... or sheltered?=20
Subject=20 to dripping- e.g. from trees?=20
Run=20 off. Look at the lichens on house roofs. Where rainwater (acidic) has = washed=20 over the lead flashing around chimney stacks, is the roof below free = of=20 lichens? Are any lichens lead tolerant?=20
Other=20 dropping modifiers. Look underneath bird perching or roosting = branches. Does=20 the constant fall of bird droppings (nitrogenous) affect the lichen = profile=20 compared to areas clear of the 'dropping zone'?=20
North,=20 east, south or west? Apart from the prevailing wind direction this is = linked=20 to the amount of sunlight. Is it also linked to predominant = wavelength?=20
Shade.=20 Would lichens on substrates beneath a tree canopy receive all the = wavelengths=20 or would some have been absorbed/reflected by the leaves? Think of the = range=20 of colorations of seaweeds. some are brown, = some=20 green, and so on. Think back to leaf pigments.=20
Pollution.=20 Many lichens have been identified as useful 'indicator = species'.=20 Remember that it is the absence of species rather than the = presence=20 which is significant. Some lichens just cannot survive in polluted = air. But=20 which pollutants? You need to find out! Remember too, in some cases = lichens=20 sensitive to acid rain can hang on if they are attached to a = substrate=20 which 'buffers' the effect.

Churches are useful = places
Those who know me as an active Christian won't be = surprised=20 at this atatement! But apart from the = obvious and=20 intended use of churches, most Amglican = Parish=20 Churches have one thing in common. They are usually built with the = longest side=20 on an east-west axis. Inside the church the left hand side of the=20 altar/communion table is north. This means that it is easy for you to do = a=20 preliminary visual check for lichens on the outside faces of a church. =

Are=20 there more or less lichens on the north or the south side? Check = back to the=20 previous section for possible reasons.... and a hypothesis you could = test.=20
Is=20 one colour - yellow for instance, more common on one face than the = other? If=20 it looks like it, you have the germ of your hypothesis. You then = need to=20 consider how you will sample(not dealt = with here=20 beyond saying that you will almost certainly be checking = percentage=20 cover using a 'bullseye' perspex quadrat). =

Another=20 thing about Churches is the range of substrates.

The=20 type of stone,=20
the type of mortar used to stick the stones in = place=20 (this may be a calcareous lime mortar-will this counteract = acid=20 rain?).=20
You=20 will also probably find 'string courses' on older churches. These = are bands=20 of different types of stone... are the lichens different here? Why = might=20 this be? Test it!=20
While=20 doing your preliminary inspection, see if there seems to be any = relationship=20 between height above ground level and types/numbers of lichens = found.=20

And=20 remember - there are lots of them! Some studies have sampled lichens = on=20 Churches at different distances from a city centre or factory. As = distance=20 increases and, presumably pollution decreases, what happens to the types = of=20 lichens found?
More gloomily- churches have graveyards. = Graveyards=20 have gravestones. Gravestones are indelibly inscribed with the date of = death=20 which is usually within a year or so of the date the stone was actually=20 installed. You will also find a marvellous range of substrates-from = finest=20 smooth marble, through portland stone and = sandstone to=20 simple wood(rare). Be careful to standardise- = if you=20 are comparing rate of growth stick to the same substrate!
Gravestones = are=20 also (but not always) often geographically arranged so the face with the = writing=20 faces the church. Interestingly the vicars's/rectors=20 are traditionally buried with their head end closest to the church so = they can=20 still proclaim the Word to the members of their flock who have their = feet=20 nearest the church so they can still receive the Word.
Exercise caution and sensitivity about using=20 churches!

Don't=20 scrape away at church walls or gravestones. Apart from being deeply=20 upsetting and offensive to many, you are also interfering with = ecosystems!=20 It is NOT NECESSARY to remove lichens.
Don't=20 assume that the lichens on a gravestone dated 1800 are over 200 = years old!=20 The stone may well have been cleaned - AND lichens do not necesarily start growing the moment the stone = is set in=20 place. The stone may have been weathered first. You will probably = never be=20 able to establish the previous history so be sensible with your = hypothesis.=20
Take=20 into account changes in the surrounding area. The church wall = lichens may he=20 been subject to sulphur dioxide pollution from a nearby brickworks = until=20 fairly recently, when the works closed down. Do some research! = There's a lot=20 to be said for sticking to a locality you yourself know the history = of.=20
Be=20 prepared to tell the vicar and/or churchwardens what you are doing! = In these=20 days of church thefts the last thing you want is the screaming = arrival of=20 police cars in pursuit of someone suspected of 'casing the church' = for a=20 robbery. "I am just checking the lichens, officer", sounds a bit = thin to=20 most magistrates, when read out in court!

Lichens offer loads of scope for = demonstrating your=20 skills at planning, standardising and executing and evaluating an = investigation.=20 For A2 you can also easily use a statistical test to support your = analysis. They=20 carry the basis for a really high scoring investigation.At least give lichens some = thought!
Happy=20 planning!

As always, you can email me for assistance with = developing your=20 project ideas.

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