Not much, you’d think, but look at these two plants!

On the left is Thylacospermum caespitosum growing at around 5300 m in Ladakh, and on the right is an acrocarpous moss (probably Amphidium mougeoti) growing on boulders below Cauldron Snout, in Upper Teesdale.  Thylacospermum has to cope with very low temperatures so its cushion shape helps trap heat around the crucial growing parts (see Cushion plants as nurses?) but both plants specialise in growing where soil and water are very limited.  The upper side of a chunk of basalt can be a mini desert just as much as a scree slope in true desert conditions. I have to admit that Upper Teesdale, on Saturday, didn’t look much like a desert though.

Left, scree below Taglang La pass, Ladakh (5300 m).  Right, Whin Sill boulders, Upper Teesdale

Another thing that seems like a common adaptation, initially, is the red colour of some plants. In Ladakh, we saw Xanthoria lichen using carotenoids to protect its algal cells from excessive visible and UV light at altitudes of 4000-5000 m.  It was noticeable that, as we climbed higher, the lichens became darker orange in colour (see More weird and wonderful lichens).

Xanthoria elegans, Ladakh

An alga called Chlamydomonas nivalis, which uses a carotenoid pigment to allow it to grow on the surface of snow, is responsible for the dramatic, bright red streaks known as ‘watermelon snow’ in the USA and plain old ‘red snow’ elsewhere. The red pigment not only acts as a sunscreen, it also heats up as it absorbs solar radiation so snow melts faster in these patches in the summer. This provides the growing alga with a ready source of water – great for the alga, but less good for climate change.  A study by Stefanie Lutz and her colleagues at Leeds University suggests the red snow may decrease albedo (how much light the snow reflects) by as much as 13 % and may well contribute significantly to the rate at which snow is melting as the world warms.  They argue that it’s time to start including watermelon snow in the models we use to look at the possible impacts of warming.

Watermelon snow (and Penguin!), Neko Harbour, Antarctica
Jerzy Strzelecki (Own work) [GFDL CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)%5D, via Wikimedia Commons

I’ve noted before that the willowherb in my allotment has startlingly bright red leaves at this time of year (see Note to self) but I’ve never seen heather the colour we found growing alongside the Tees at Cauldron Snout this weekend.  The first plant we saw was so bright I worried that someone had spray painted it red as a marker of some sort, but a closer look confirmed it was absolutely natural.  In fact it’s only the upper surface of each branch that is red; the underside just has a delicate red edge.

Heather, Calluna vulgaris, growing in Upper Teesdale – the photo on the right shows the upper and lower surface of a branch

There is debate about how much protection this red colouring, due to anthocyanin pigments, offers against bright sunlight.  The hairs which cover many young leaves are believed to have a more significant effect, by diffusing the sunlight. Anthocyanins are probably more important in protecting the tender, early-season leaves from insect attack.

It’s interesting that plants growing together, like this, can have such different approaches….

Lutz, S. et al. (2016). The biogeography of red snow microbiomes and their role in melting arctic glaciers. Nature Communications 7, Article number: 11968 doi:10.1038/ncomms11968