The two Marys at Basturs gran lake

It has been said that ultimately we all came out of the sea. Why then are so many land plants, including many of those on which we depend for food, unable to survive increased salinity in the soil? This is an important question, since between 2.3 and 6.4 % of the Earth’s total land surface is saline – an enormous amount, and one which continues to steadily increase, especially in Australia. Some answers may be found in the behaviour of giant-celled green algae, the charophytes or stoneworts, which are widespread in ponds, dams, creeks and lakes of the world.

The charophytes are the living relatives of the algae that evolved into all the land plants amongst us today. Some, like Lamprothamnium succinctum, tolerate salinity and thrive in marine as well as freshwater environments. Others, like Chara corallina, quickly die in saline waters. The ability to cope with salinity is reflected in the electrical behaviour of the cells, and the comparative electrophysiology of salt-tolerant salt-sensitive charophytes has long been a focus of my research. Up to date I am finding that the differences between these charophytes are surprisingly subtle. The ability to cope with varying amounts of sodium salt in the environment is clearly very useful. How did it evolve?

In 2004 I joined the International Research Group on Charophytes (IRGC). This group is mainly concerned with fossil charophytes, and classification and ecology of living charophytes. This connection has added an evolutionary dimension to my research. Last October I headed to Barcelona to take part in the 14th meeting of European branch of the IRGC and met up with my USA collaborator, Mary Bisson.

My talk on electrophysiology provided somewhat different fare from the ecology and systematic botany that is usually featured. In turn, I was interested to learn that the charophytes were around in the time of the dinosaurs and probably served as food to some of them. I was amazed at the variety of modern charophytes and their habitats. There are many salt-sensitive genera, some brackish genera and only a few truly salt – tolerant genera, mainly in the Lamprothamnium genus.  I was also interested to learn about charophytes growing in high concentration of potassium salts. I have investigated the electrophysiology of this situation, but did not realise it exists in nature. As to whether the original ancestral charophytes were salt-sensitive or salt-tolerant, there are gaps in the fossil record and so, no-one yet knows.

After the talks the organisers took us to the Pyrenees Mountains. On the first day we visited two karstic lakes. These looked volcanic in origin, but were created by a deep aquifer emergence, recharged in the high mountains nearby. We collected some living charophytes, including rare Lychnothamnus barbatus.

As the sun was setting we drove to the La Cerdanya basin, the widest valley in the Pyrenees. The valley used to be a paleolake with the bottom deposits dating within 10 - 13 million years ago to higher deposits dating within 4.9 - 6.8 million years ago. We made several stops and looked for fossils – my first experience with a geologist’s hammer. Only in the last stop did we find fossilised charophyte fruiting bodies and ghostly white impressions of the whole plants of Lychnothamnus. What magic to gaze upon a plant imprint imprisoned in the rock for millions of years! A living relative of this ancient charophyte was recently found in Australia and is thought to be salt-sensitive. Its electrophysiology might be worth studying!

Mary Beilby