Dear members and friends of the DMG,

Today, there is a bit of science in the greeting. Because I am writing it during the summer break, when there are no groundbreaking developments from society to report. It's about plants (!), which we are working on in our group "Geochemistry of the Earth's Surface" at the GeoForschungsZentrum Potsdam, and what they have to do with mineralogy. Maybe some of you are interested in what your DMG chairman is actually up to scientifically. I will start with a question.

What is the largest transfer of dissolved chemical elements at the Earth's surface? For "surface geochemists," the first choice is probably the elements released during rock weathering, which are carried to the sea by the major rivers. And what controls the size of these transfers? Well, the standard answer would be, first, mountain building and erosion, which is correlated with weathering, and second, precipitation and the carbonic acid it contains, so a climatic control.

As part of the DFG priority program "Earthshape – Earth Surface Shaping by Biota," which I co-coordinate, we have investigated another regulatory mechanism. Plant growth leads to higher carbonic acid content in the soil, which accelerates mineral dissolution. Higher plants also require the essential mineral nutrient phosphorus and other vital elements such as potassium and magnesium, and even silicon, which is stored in leaves as "phytoliths" in amounts of up to percent as a defense against grazing animals, or to provide structural stability. To access these nutrients, the roots live in symbiosis with fungi, called "mycorrhizae," which release these elements from minerals for the plants and, in return, receive energy thru carbon – a brilliant trade-off by nature.

So the hypothesis was obvious: the more plant growth, the more rock weathering. We measured this in the focus program in Chile along a massive vegetation gradient, and, far from it: rock weathering does not increase with plant growth. Instead, we found out what great recyclers plants are (this is, of course, well known in ecology). The more plant growth, the more frequently elements are reused. If they fall to the ground in leaf litter, they are directly reabsorbed from it. Globally speaking, an element like potassium moves thru the global biomass about 20 times after being released thru weathering before it is transported in a body of water, phosphorus even 100 times, and even silicon about 5 times. The answer to my question above is: not the rivers - plants conduct the largest material flow on the Earth's surface!

Why are we even dealing with this question? First of all, plants fractionate the stable isotopes of these elements during uptake. For magnesium, iron, silicon, strontium, and other metals, this is now well known, and the effect of plant uptake on the isotopes of the weathering zone interests us in order to derive mass balances from it. But that's another story. Much more significant is quantifying the delicate balance between the living world and the geological world here in the "Earth System," a system whose functioning is currently in great danger due to human interventions. We simply have to deal with this – also as a DMG topic. And finally, one can simply admire how natural systems have established a resource-conserving "circular economy," which we wasteful humans can only dream of. Better still, we could take a leaf out of their book for our economy. As soon as possible.

Best regards, Yours, Friedhelm von Blanckenburg

PS: In November, there are elections for the DMG board, advisory board, and committees. Please participate. Information at www.dmg-home.org