Link to paper: https://doi.org/10.1038/ncomms3614. The underlying reason for this seems to be that Eucalyptus roots are unusually deep and aggressive (something I have personally witnessed), and any gold they pick up is toxic and gets transported to the leaves, where it can’t do as much harm.
Totally a tangent but as an Australian I'm amazed at how common eucalyptus trees are in California. They were introduced just 150 years ago and parts of California have denser eucalypt forest than Australia now. Which isn't good for California's bio diversity and given the flammability of eucalyptus is bad from a safety point of view too. There should be more of an effort to remove them.
Unlike eucalypts in Australia, in California and Hawai'i nothing eats them. Tasmanian bluegum is the most common eucalypt in that range [0]. Therefore a) they grow very rapidly, and b) are useless as structural or furniture woods. The Berkeley Hills "Tunnel" fire of 1991 [1] was driven in large measure by the presence of eucalypts. In much of northern California today, eucalypts are seen as large flammable weeds.
We would do better to grow Acacia acuminata, Raspberry Jam Tree, in SoCal. It grows fast, and smells like raspberry jam when sawed. Australia has millions of century-old A. acu. fenceposts, 'cause they last forever. Carbon capture! The wood (like most acacia) is excellent for furniture.
We used to have tons of eucalyptus trees in my hometown in northern Mexico. Then an unusual winter arrived 10 years ago, temperatures dropped to -24 Celsius. All the eucalyptuses died and with them a big percentage of our vegetation and shade. I don’t know why we are so obsessed with foreign flora in our cities.
They're also all over southern China - https://www.fao.org/3/AC772E/ac772e04.htm suggests over 1.5 billion. As well as eucalypts there are really a huge amount of street plantings of Aussie Myrtaceae, such as bottlebrush and paperbark. All are deep rooted trees, they will seek water to impressive depths. Casuarina as well, although the predominant species is endemic to much of Asia and apparently Gondwanan.
It's the same in parts of Spain. You take a walk in the wild, hoping to experience the local flora, and you find yourself surrounded by these highly flammable trees that have travelled as far as you have to get there. Pretty, but no more so than the displaced native flora, and disastrous from an environmental or fire management point of view.
I'd hazard a guess that that is precisely why it's toxic to plants. It brings to mind things like Lead poisoning for us, because it takes the place of calcium in the body to horrific effect. And it just never really goes away. Meaning it doesn't really react with anything much, since that would reduce it over time. IIUC of course.
That said, I'm sure lead isn't the best example, since I am merely hazarding a guess right now.
For the Eucalyptus plant, sending the gold to the leaves is probably a good way to get the gold out of the way for more important nutrients to get where they need to go. Worst case scenario for the plant, it loses a few leaves. Which is something it already had to deal with before through Koala bears.
Thats not true. Gold won't patina but it can react with things. It can replace other metals in key enzymes which will inhibit their function. You can also use it as a catalyst both heterogeneous (as nanoparticles) and homogeneous (as an organometalic complex).
Well thats just the thing, if a gold atom were to replace say a copper atom in the active site of an enzyme, it would behave differently and more than likely in a deleterious manner.
