We took advantage of the quiet mornings at Latitude to drive off the site and explore the countryside around Southwold. I had memories of a family holiday here in 1968 and little seems to have changed: it is traditional seaside town, seemingly frozen in time, with a pier, beach huts (as in the image above), a lighthouse and a row of cannons facing out into the North Sea.
As we followed footpaths along the dykes beside the creeks, I noticed a red mat of vegetation covering the surface in one of the stagnant areas close to the A1095. Closer inspection revealed this to be the floating fern Azolla filiculoides, an introduced plant that is quite common in the south of England but which is an unusual sight to an adopted northerner such as myself (see also “No longer a dispassionate observer of nature…”). Inevitably, I was soon down on hands and knees to pull out a small sample for closer inspection.
Azolla filiculoides in Buss Creek near Southwold, July 2016.
When seen in close up, each individual plant is about a centimetre across, but is composed of tiny fronds, each no more than a couple of millimetres in size. Long hair-like roots hang underneath the plant. The red colour is due to pigments called anthocyanins, which belong to a class of compounds called flavonoids and which offer the plant some protection against very high light intensities (an alternative strategy to that seen in Cladophora in the previous post). Interestingly, anthocyanin production also takes place in response to low temperatures, possibly because the generally low metabolism of the plant under such conditions leads to the same build-up of excess energy when there is abundant light, because the cell machinery is grinding along at too slow a pace to keep up with photosynthesis.
Left: collecting Azolla filiculoides from Buss Creek near Southwold, July 2016; right: fronds of Azolla filliculoides in the palm of my hand.
One of the intriguing features of Azolla is that it, along with the pea family and a few other groups of organism an ability to fix nitrogen. This allows it to grow in habitats where nitrogen, a naturally scarce plant nutrient, is in short supply. Like the pea family, Azolla does not, itself, capture and transform nitrogen into the compounds it needs to grow, but carries a complement of passengers who do this work for the plant. The symbiotic organism in the case of Azolla is the cyanobacterium (blue-green alga) Anabaena and I was keen to have a closer look at my Azolla to see if I could tease these out. However, as I mentioned in my previous post, festival conditions are far from ideal for preserving fragile plant specimens, and my material was not in a very healthy state by the time I got it under my microscope.
The blue-green filaments of Anabaena were, nonetheless, conspicuous, once I had squashed a few fronds gently under a coverslip. Anabaena is a close relative of Nostoc (see “Nosing around for blue-green algae …”) and also forms long chains of bead-like cells that resemble rosaries. Look at the photograph below and note how there is a larger cell spaced at intervals along each filament. These are the “heterocysts”, the specialised cells that contain the enzymes responsible for nitrogen fixation. The ease with which Azolla grows in damp habitats, particularly in warm climates, and the ability of “Team Anabaena-Azolla” to catch large quantities of nitrogen means that Azolla is grown as a “Green Manure” in some parts of the world, as it bypasses the need to buy expensive artificial fertiliser.
Anabaena filaments from a squashed frond of Azolla filiculoides from Buss Creek near Southwold, July 2016. Scale bar: 10 micrometres (= 1/100th of a millimetre).
Sample safely collected, we followed the dyke across the marshes (all slightly below sea level here) until Buss Creek joined the River Blyth and we then turned towards the sea. As we reached Southwold Harbour, we found a small café offering fresh crab sandwiches, which sounded too good to resist, even though it was barely 11:00. And, from there, it was just a short walk back to Southwold. A few kilometres away, the Latitude Festival was getting under way again, and our brief sojourn in Southwold had to be curtailed in favour of other attractions, culminating in a rather impressive headline set by The National. For one weekend in the year, at least, Suffolk is not quite the boring county that most of us think.
Janes, R. (1998). Growth and survival of Azolla filiculoides in Britain. 1. Vegetative reproduction. New Phytologist 98: 367-375.
The National’s headline set from Latitude 2016