Autumn/Winter 2011/12 - Harcourt Arboretum - University of Oxford

16
Botanic Garden News | No. 79
The last word
by
Timothy
Walker
F
erns such as Azolla that are featured
in this edition’s “A few words” may
be an ancient group of land plants
with an illustrious past but they are
new kids on the block compared with their
nitrogen-fixing cyanobacteria lodgers. The
cyanobacteria belong to a very ancient lineage
of living organisms that have had an even
more profound influence on the Earth and its
biology than has Azolla.
Cyanobacteria, also known as blue-green
algae or blue-green bacteria, have been
described as “arguably the most successful
organisms on Earth”. This claim can be
Gunnera leaves in the Bog Garden cut and laid down to protect the rhizomes over winter
supported by the fact that they are found in
almost every habitat from seasonally dry,
bare rocks in cold regions to hot springs
where life should not exist. Moreover, fossil
cyanobacteria have been dated at more than
3,000 million years old. Part of their success
has to be due to their ability to photosynthesise
and fix atmospheric nitrogen. It is
believed that their photosynthesis has made
a significant contribution to current oxygen
levels in the atmosphere.
You might wonder why gardeners should
be interested in these little organisms.
The answer is simple: about 1,200 million
years ago one of these photosynthesising
cyanobacteria was engulfed by another
single celled organism but rather than being
digested and broken down, the cyanobacteria
remained intact and was press ganged
into a symbiosis. This cell was the first plant
and had this endosymbiotic event not
happened our gardens would be empty.
Another species of nitrogen fixing cyanobacteria,
Nostoc punciforme, lives in the vast
leaves of Gunnera manicata which has grown
bigger this year than anyone can remember.
It is one of those odd quirks of biology that
the tiny leaves of Azolla and the huge leaves
of Gunnera both contain cyanobacteria.
Perhaps cyanobacteria could be introduced
into crop plants to replace the need for
nitrogenous fertilizers
University of Oxford Botanic Garden
November to February:
open daily 9.00am to 4.30pm,
last admission 4.15pm
March, April, September & October:
open daily 9.00am to 5.00pm,
last admission 4.15pm
May to August:
open daily 9.00am to 6.00pm,
last admission 5.15pm
We are closed on Christmas Day
and Good Friday
No dogs allowed in the Garden
(except assistance dogs)
University of Oxford Botanic Garden
Rose Lane, Oxford OX1 4AZ
Tel: 01865 286690
E-mail: postmaster@obg.ox.ac.uk
Web: www.botanic-garden.ox.ac.uk/
Garden/obg-intro.html
University of Oxford Harcourt Arboretum
December to March:
open Monday to Friday 10.00am to 4.00pm,
last admission 3.30pm; closed weekends
April to November:
open daily 10.00am to 5.00pm,
last admission 4.15pm
We are closed 22nd December to 3rd January
No dogs allowed in the Arboretum
(except assistance dogs)
University of Oxford Harcourt Arboretum
Nuneham Courtenay OX44 9PX
Tel: 01865 343501
E-mail: postmaster@obg.ox.ac.uk
Web: www.botanic-garden.ox.ac.uk/
Harcourt/obg-harcourt-intro.html
The Friends of Oxford Botanic Garden
and Harcourt Arboretum
Rose Lane, Oxford OX1 4AZ
All Friends’ enquiries, including those about
Friends’ events, should be made to Liz
Woolley, the Friends’ Administrator
Tel: 01865 286690
E-mail: secretary@fobg.org
Web: www.botanic-garden.ox.ac.uk/
Friends
Please note that the Friends’ office is staffed
only on Tuesdays and Wednesdays, between
9.00am and 4.00pm. At other times urgent
Friends’ enquiries will be dealt with by
Garden staff.
The newsletter is published by the University of Oxford Botanic Garden and is edited by Liz Woolley
and Timothy Walker. The views expressed in articles are those of the authors and do not necessarily
reflect the policy or views of the Visitors of the Botanic Garden.
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