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The natural defenses of dead plants -- which are designed to inhibit enzymes in the gut to prevent digestion -- would be toxic for any other animal. But a group of researchers from Imperial College London have discovered new molecules in the worm gut, named drilodefensins, that can counteract the toxins, breaking them down the way that dish liquid breaks apart grease.
"Without drilodefensins, fallen leaves would remain on the surface of the ground for a very long time, building up to a thick layer," said Jake Bundy, an author of the study and a professor at Imperial College, in a statement. "Our countryside would be unrecognizable, and the whole system of carbon cycling would be disrupted."
The humble worm is amazing. It can turn lawn waste and food scraps into rich black soil in a matter of weeks.
(Score: 5, Interesting) by acid andy on Thursday August 06 2015, @10:36PM
Perhaps I'm being unfairly pendantic here (again), but why would dead plants need natural defences from an evolutionary point of view? Are they defences that were in use whilst they were living that have just remained in death? I know deciduous trees pass toxins into their leaves to remove them from the tree but I don't see how that's relevant here.
I would have thought that it might be advantageous to feed predators on discarded dead leaves in preference to foliage that is still in use.
Master of the science of the art of the science of art.
(Score: 1, Interesting) by Anonymous Coward on Thursday August 06 2015, @11:50PM
One possible explanation is that un-decomposed dead leaves for a barrier on the ground to new plants springing up to compete with the tree. So the tree has some incentive to have leaves that fall not decompose for a time - especially over winter.
(Score: -1, Flamebait) by Anonymous Coward on Friday August 07 2015, @12:47AM
Such an intelligent design, these trees have.
(Score: 0) by Anonymous Coward on Friday August 07 2015, @06:18AM
Plants cannot see or plan ahead of time and cannot see the consequences of their actions down the line, the way humans do.
After a leaf falls, the tree cannot know what happens to it, because it is now disconnected from mothership. It only knows what is currently happening and how its actions change what is happening to the plant (while interacting with something else, like an animal).
To stop other plants from growing in the vicinity would require careful planning, where the plant would fill its leaves with poison and then drop them, hoping that the tree growing near would get killed by it, or not grow at all.
That said, I cannot totally explain how the plant gets its seeds delivered to faraway places (using carriers such as animals and wind), as that would require careful planning. But one explanation is that the tree noticed what happens when seeds fall right next to it and start growing there, competing for resources. The trees that continued to let seeds fall right next to it gradually killed themselves off, allowing the tasty seed plants to flourish.
The planet's been around a long long time.
(Score: 3, Insightful) by wonkey_monkey on Friday August 07 2015, @09:26AM
Have you ever heard of this new idea called "evolution"?
Trees don't know anything. They can't plan at all, regardless of whether they or their constituent parts are alive or dead (which, incidentally, is not always a simple binary distinction). They don't need to. Random mutations - such as leaves which don't decompose quickly - occur and confer advantages or disadvantages which end up being propogated (or not) through the generations.
But one explanation is that the tree noticed
That's a pretty terrible explanation.
systemd is Roko's Basilisk
(Score: 1) by purpleland on Friday August 07 2015, @02:17AM
One explanation is that the tree wants to prevent growth in its immediate vicinity for purely selfish reasons. Leaves dropped in fall that survive well into spring will suppress new saplings/plants from growing, thereby reducing competition against established trees.
(Score: 1) by purpleland on Friday August 07 2015, @02:20AM
Just noticed earlier poster mentioned same thing, but yeah.. this makes sense.
(Score: 2, Interesting) by purpleland on Friday August 07 2015, @02:30AM
If you could devise a simulation (possibly using a genetic algorithm of some sort) of trees with leaves containing this enzyme vs trees without, to demonstrate its effect is directly responsible for creating the most successful (i.e. biggest) trees - couldn't you get published in Nature or something?
(Score: 3, Insightful) by TheLink on Friday August 07 2015, @03:09AM
You could do this in different ways without affecting the ground below e.g. suspend nets below tree branches.
(Score: 1) by purpleland on Friday August 07 2015, @04:30AM
Yes, indeed and I wonder if there are other implications as well... like wouldn't a long lasting dense leaf cover on the ground help keep the soil a bit warmer, thereby protecting its surface roots from the cold?
(Score: 2) by moondrake on Monday August 10 2015, @08:41AM
The problems with such simulations (I do a lot of those) is that you can only model things you already know about (and often only imperfectly). Nature sometimes does things that we do not know about, and thus they cannot be put in a model. Even if the model gives you the expected outcome, it might be for the wrong reasons (especially since you are likely dealing with a gazillion parameters that you have only approximate estimates for).
(Score: 4, Informative) by moondrake on Friday August 07 2015, @09:17AM
its just some silliness from the summary (or perhaps its in the WP already). I am not aware of any proposed function of polyphenols (which is the toxin the original paper [nature.com] talks about) in dead leaves. They are however well-known protectors against herbivory in living plants.
I do not think the polyphenols are itself are a problem for germination or plant growth, so a role in preventing other plants from growing on leaf litter (as proposed by a sibling here) seems unlikely (polyphenols bind and precipitate soluble proteins, for that they need to be in direct contact with such proteins, so inside cells, or inside a digestive tract. Plant cells will not absorb them though, and plants do not have a digestive tract).
Under most conditions, plants are not carbon limited, and thus polyphenol components are not worth recycling from the leaves (it would probably very hard to do so practically anyway). Biologist tend to try and make everything "functional", but lets not forget that in many cases, things just evolved because they did not affect the survival of the species negatively (or negatively enough). This is not to say that it is impossible that polyphenols in litter have a function, just that I think there is currently no evidence for it.
This all seems a little bit like an alien hypothesizing we put old cleaning utensils in the garbage to make sure the garbage truck stays clean.
Disclaimer: I am a botanist (though not a phytopathologist)