Old trees, ancient algae

Botanists on the US west coast have found that blue-green algae living on mosses, which in turn live on old trees, keep forests alive and healthy.

As reported by ScienceDaily, Zoë Lindo and Jonathan Whiteley, from McGill University, are studying the way nutrients like nitrogen move around old-growth forests growing from southern Alaska to northern California.

We all know, don’t we, that blue-green algae (or cyanobacteria) ‘fix’ nitrogen from the air, turning it into nitrogen compounds that other plants can use? Nitrogen, in its right form, is one of those things that can limit growth (like phosphorus in Australia, where many crops can only be grown if huge amounts of superphosphate are added to the soil).

Blue-green algae have been on earth for maybe three billion years, producing the first biological oxygen and pretty much starting the procession of life on this planet. Today they live all over the place, including hot springs, slippery paths and in stagnant water. They also live in the roots of some plants, such as cycads. More relevant to this story, they live inside some mosses.

It was already known that blue-greens living in mosses growing on the ground were important sources of nitrogen in mountain forests. This study by Lindo and Whiteley shows they are just as valuable in coastal forests and in the canopy of trees.

In fact, blue-greens in mosses 15 and 30 metres up are more productive than those on the forest floor. In fact they fix about twice as much as their ground-dwelling relatives.

Although the algae are important, of course, they can’t do this without the mosses and very old trees. The botanists apparently argue that many trees need to be more than 100 years old before they start to accumulate significant cloaks of moss, and the beginnings of this marvellous nitrogen-fixing factory. The trees they studied were 500 to 800 years old.

So we need to look after our old trees, allow them to accumulate mosses and other hangers-on, and as always, learn to love algae.

Image: I don’t know what cyanobacterium was found in these high-rise mosses (the scientific article is pay-to-view and I’m too stingy for that) but Nostoc and Stigonema have been found in the ground-floor mosses – this is a picture of Nostoc, living alone... Thanks: to Wendy Joy for citing this story on Facebook.