Sunday, March 27, 2016

A World from Dust (Update): Should the White Rot Story Change?

One of the hazards and joys of science writing is that what you write will change in some way after publication. The first one of these just happened. A paper just came out that may change one of the sections in A World from Dust Chapter 9, from what was explained as a biochemical cause to what is more a geological/climate cause. In the book, I put forward the explanation that so many plants grew so big in the Carboniferous Era because they invented lignin, and it took millions of years for fungi to evolve an efficient system for degrading that lignin, so it eventually turned into coal deposits till the fungi evolved. This is what most people thought, and it was backed up by a recent phylogenetic analysis.

But wait! M.P. Nelson et al. just published "Delayed fungal evolution did not cause the Paleozoic peak in coal production" in PNAS. The title speaks for itself -- Nelson et al. have produced an impressively integrated array of sciences to argue that most of the biomass wasn't lignin anyway and also that many lignin-degrading activities did evolve quickly. Rather, they propose that wet climate related to geological activity resulted in the unprecedented burial of carbon as coal. As a scientist outside the field, their argument seems compelling because it depends on bringing together so many lines of evidence.

My only hesitation comes from another paper I saw during the same reading session: Nagy et al. in Mol Biol Evol titled "Comparative Genomics of Early-Diverging Mushroom-Forming Fungi Provides Insights into the Origins of Lignocellulose Decay Capabilities." This paper suggests that white rot evolved later than previously stated, although I don't find many dates to pin down just how much later they propose it evolved. If this activity is significantly better on crystalline lignin or some extra-sturdy form, the story might end up aligning in part with the book's explanation.

I'll have to see how the scientists in the field sort this one out. If, as I suspect, Nelson et al. end up with the winning story, then there is a take-home lesson that takes a story away from Chapter 9 but will reinforce part of Chapter 10: evolution tends to surprise us with how quickly it can solve problems. If Nelson et al. are right, then it didn't take many millions of years to crack the tough nut that is lignin, and fungi were able to respond much faster than I or others presumed.

I'll try to update this part as more info comes out. The book is in print, but the blog can change as science does.

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