Daniel and his den of diatoms …

After contemplating astronomy-without-optics at Ulug Beg’s observatory (see previous post) we walked ten minutes down the road to another of Samarkand’s sights, the mausoleum of Daniyar (the Old Testament prophet Daniel, also venerated by Muslims).  This was a much plainer structure than the polychromatic wonders we had seen elsewhere in the city and, no doubt as a result, fewer visitors.  Daniel’s sarcophagus runs the entire length of the building: the legend is that his severed leg has continued to grow, necessitating an eighteen metre tomb.  The presence of a group of pilgrims, praying with an Iman, reminded me that our word “holiday” is a concatenation of “holy day”, and that pilgrims were the original tourists, both in this part of the world and in Europe.

Our guidebook mentioned an ancient spring on the site, offering me my first opportunity to mix business and pleasure. Unfortunately, the spring was dry but, following the valley up a steep hillside, we reached a graveyard, beside which there was a water trough whose bottom, when I peered inside, was covered with dark brown circular patches, up to about half a centimetre across.  I had not really come prepared for diatom sampling but managed to commandeer an empty water bottle into which I scraped some of these colonies using a piece of plastic that I found lying on the ground nearby.   The water bottle was then stuffed into my rucksack as we continued our explorations, cutting across country towards another set of monuments that we could see on the horizon (Colin Thurbron describes the same journey in reverse in his excellent book The Lost Heart of Central Asia).   Once we were back at our hotel, I let the sample settle overnight, poured off the supernatant and then added an equal volume of local vodka to the remaining suspension.  As in India last year, this is the quickest and least hazardous way of keeping diatoms in reasonable condition when on the road (see “Diatoms from the Valley of Flowers”).

Left: the water trough near Daniyar’s mausoleum, Samerkand from which my diatom sample was collected and, right, the circular colonies of diatoms on the bottom of the water trough.  The largest of these colonies is about half a centimetre across.

Several freshwater diatoms form conspicuous colonies but what intrigued me about these particular growths was that the colonies were disc-shaped, reflecting horizontal growth with little vertical development.  Once back from my travels, I had a look under the microscope and was surprised to see that they were composed of almost-pure growths of either Achnanthidium minutissimum or a very close relative (my observations were on the vodka-preserved specimens and I have not yet had a chance to look at cleaned valves).   This is an extremely common constituent of biofilms all over the world but I have never seen it forming discrete colonies in this way.  I suspect that, given time, all of these colonies would merge to form a continuous biofilm and that, in a natural ecosystem (rather than a water trough), grazing by invertebrates would then control the biomass so that they formed a subaquatic and microscopic “turf”.   Maybe what I am seeing is the early stage of colonisation in a situation where there are, as yet, no grazers?   It is very hard to tell an ecological story from a single, brief visit to any habitat but that would be my opening gambit.

Microscopic views of Achnanthidium minutissimum colonies from the water trough near Daniyar’s mausoleum, Samarkand, April 2017.  The left hand image was taken at x100 magnification and shows a colony (or fragment) that is about 650 micrometres across.  The right hand image was taken at x1000 magnification.   Scale bar: 10 micrometres (= 1/100th of a millimetre).

Achnanthidium minutissimum was not the only familiar plant (in the broadest sense) that we saw on our travels.   The grazed grassland between Daniyar’s mausoleum and Bibi Khanym mosque, our next objective, contained several flowers familiar from home (see Heather’s blog) and our trip to the Tien’shan mountains a few days later revealed many more, including a steep-sided valley full of hawthorn bushes.   It is a good reminder that, however far from home we are, and however exotic our surroundings, we are still in the broad temperate belt around the Eurasian continent that allows a measure of biogeographical continuity across this area.  Some of the plants we saw in the wild in Uzbekistan are garden plants in north-west Europe (the tulip is a good example) but several others thrive in the wild in both places.

Botanising in the grassland between Daniyar’s mausoleum and Bibi Khanym mosque, Samerkand, April 2017.

Decoration on mausoleums at the Shar-i-Zinda complex in Samerkand, near the Bibi Khanym mosque and Daniyar’s mausoleum.  The photograph at the top of this post shows the exterior of Daniyar’s mausoleum.

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