For this Pensive Tuesday, I'm once again ruminating on the subject of dirt. Desert dirt, specifically. I've spent long stretches of time hiking through the desert on archaeological digs, and for other assorted reasons. The hard crust of desert soils has always intrigued me. What makes that crunchy crust? When that crust is disturbed, for instance, by vehicles, dust storms can erupt. And plants can no longer live there. So what is it about the crust in which so many Mesembs and cacti live?
Cyanobacteria.
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| Cyanobacteria (photo Wiki Commons) |
They are so ancient, these little guys, that they have been around for practically all of Earth's history. They grow into vast collectives that stabilize soils, fix nitrogen, provide oxygen, and prevent erosion in arid and semi-arid environments. They make it possible for plants and animals to colonize harsh environments. When they are destroyed, the soil is no longer hospitable to other plants and the animals that feed on the plants. Amazing!
Climate change is having an effect on these critters, but we don't know much about it yet. The main species that grows in hot deserts, Microceleus steenstrupii, should do fine for a time, but other species, equally important to the environment, might not. Hopefully, scientists are doing more research to find out what's going on in those crusts. And when you're walking over a soil crust, be sure to thank the tiny creatures that make it possible!
My college professor said, "Dirt is something you sweep up and throw away, Soil is something you grow plants in." :-) He also said that the soil crust was the result of water separating out the fine material from the larger aggregates and the fine material fits together nicely and forms the crust. In some desert areas there is also a lot of calcium carbonate in the soil and this adds to the binding of the fine particles of soil to make something like weak concrete. I think they call that caliche.
ReplyDeleteI like soils a lot too. I can't cook very well but I can whip up potting soil mixes with all sorts of ingredients. My latest ingredient has been crushed clay pots. I break the pots up into pieces of 5 to 15 mm in size, and I have used that (about 20% by volume) in some of my latest lithops potting mixes. At least it recycles old dirty clay pots.
Cyanobacteria were probably the pioneers of life. I've heard several biologist say that if intelligent aliens from another world came here they we view cyanobacteria the most important life form in earth, not humans. Thanks for a great pensive Tuesday topic!
Bob
I'd always liked caliche since my archaeology days, made trekking so much easier, but had assumed it was biologically inert except for scrubby little plants that I could see...I had no idea that cyanobacteria could thrive in such stuff, or that it was such a vital component. I'm glad it's finally getting some proper study. They really are the pioneers of life!
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