(This post may seem a bit rambling, but the overall theme is the joy of learning.)
Since March this year I’ve been doing a weekly photo blog for a local nature reserve. By Autumn, I’m rarely finding any new plant species to report, and so my attention has turned to fungi, about which I never really thought very much, except to find the idea of eating wild fungi rather scary.
However, I have thought about lignin, and how so many different plant families seem to carry the genes to synthesise it – and on looking it up on Wikipedia, it seems pretty well all do. I’m interested by lignin, because of its role in forcing plants to enter into an arms races with each other, wasting resources building taller and and more massive trunks to support leaves high up in the canopy, competing for light. It’s my favourite example of nature not being harmonious, however beautiful we find it.
I was thinking about this in connection with the Earth’s evolutionary history, and how this arms race will have led to the sequestration of more and more carbon, which from my reading of popular science I guessed would have been what was happening in the Carboniferous era. But thinking about fungi this Autumn, which seem to be just about the only organisms which can digest lignin, I started speculating about how their evolution fitted into this picture. Fungi were around long before the Carboniferous, and many, such as yeasts, have nothing to do with lignin, but did some evolutionary step happen with the fungi Kingdom to take advantage of the vast new opportunity which the growth of the forests was presenting?
Well, a contact I’ve made in connection with this photo blogging is a researcher who is developing a new way of assessing bio-diversity by making audio-recordings, and who, in conversation, mentioned the site ispotnature.org as a place to go for expert help with identifying species. So I have now joined, and know quite a bit more about fungi than I did. Then last week I ventured onto an ispotnature Forum to ask about the co-evolution of woody plants and fungi, and in due course was directed to this paper in Science Magazine.
from which I found the following clade tree, backing up my guess
(I know it’s not clear from this, but the colour strip at the bottom is a time line for geological eras, with Carboniferous the pale blue in the middle. Above the clade tree explodes into numerous new taxa with the capacity to attack wood starting from that era. And strictly speaking, brown rot doesn’t actually degrade lignin – that’s just white rot.)
The paper concludes
Organic carbon accumulated at an exceptionally high rate during the Carboniferous and Permian, resulting in the formation of vast coal deposits, derived primarily from lignin. A frequently cited explanation for this phenomenon is that decay was inhibited in the anoxic sediments of widespread coastal swamp forests. Our results are consistent with a complementary hypothesis, which posits that the sharp decline in the rate of organic carbon burial at the end of the Permo-Carboniferous was caused, at least in part, by the evolution of lignin decay capabilities in white rot Agaricomycetes
From which it follows that fungi will also have had a role in reversing the cooling which went on in the Carboniferous era