Country diary: venerable beech hosts a swarm of microscopic life | Environment

The beech that stands at the end of the stepping stones across Waskerley beck is an elephantine presence, dwarfing surrounding trees. The scarred grey bark of its bole has the colour and texture of pachyderm skin. Its moss-covered surface roots seem to be melting into the earth under the massive burden they support. Over decades they have grown and coalesced, creating hollows between them that retain water, fed by rivulets of rainwater trickling down the trunk.

There is a name for these mini-ponds that form on the surface of plants and are habitats for small aquatic organisms: phytotelmata, which translates from the Greek root as “plant ponds”. The best studied are those contained by leaf bases of urn plants or bromeliads that live on branches in rainforest tree canopies. They are breeding sites for frogs, dragonflies and even land crabs.

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A
phytotelma (water-filled cavity) contained by coalesced surface roots of a beech tree. Photograph: Phil Gates

Beech root phytotelmata rarely host anything larger than fly larvae, but the microscopic organisms that live in them all year round are no less remarkable. I scooped out a sample of stagnant water from one and took it home for a closer look.

When the water cleared I could see minute crustaceans, wriggling nematode worms, the larvae of midges and a fuzzy mist hovering over the surface of the settled sediment. I pipetted a drop of that cloud on to a microscope slide.

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Swarm of the single-celled organism
Colpidium colpoda magnified 100 times. Photograph: Phil Gates

As I focused, at a magnification of 100 times, an astonishing spectacle swam into view. The mist was a dense swarm of Colpidium colpoda, a single-celled organism propelled by rows of rhythmically beating cilia. Colpidium feeds on bacteria, so perhaps something had died in this phytotelma and created a nutritious bacterial soup.

Swimming Colpidium from a beech root phytotelma

To see so many of these minute organisms moving so fast in such a confined space was akin to watching manic funfair bumper cars, endlessly colliding and reversing.

Colpidium is about 20 thousandths of a millimetre long. One million of these tiny organisms laid end to end would reach from the roots of the century-old beech that hosted them to its uppermost twig. The other-worldly beauty of such life forms, whose individual existence is measured in hours, and which no one would have been aware of before the invention of microscopes, never ceases to amaze.

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