Cryptobiotic Soil Crusts

Very informative post by Chris Clark on "Cyanobacteria, the desert soil, and you" at Pharyngula. I learned a lot. I'll include a bit of Clark's post below, but the whole thing isn't all that long ... and it's good.

Soil crust in Utah | J. Brew photo

"Cryptobiotic soil crusts, also referred to as cryptogamic soils, or just plain “crypto,” are pretty common in arid lands that haven’t been disturbed for a while. They’re alive, as indicated by the  suffix “biotic”: living communities of half a dozen different kinds of organisms: cyanobacteria, green and brown algae, fungi, lichens, mosses and liverworts. The “crypto” part means that when conditions are less than optimal, the organisms that make up the crust can go dormant, seeming to die off — “hiding” their life. Cryptobiotic.

"The crusts develop in places where there isn’t enough moisture to maintain a soil vegetative cover: no trees, no sod, no leaf litter, no humus. They usually start with filamentous cyanobacteria, which grow mats similar to fungal mycelia penetrating the top inch or three of soil. Cyanobacteria photosynthesize and many of them fix nitrogen, so  all they need to grow is water and a few soil nutrients. When it’s wet they extend their filamentous sheathes into the soil, which is exactly as sexy as it sounds, and then when the drought comes the cyanobacteria shrink back but the sheathes — made of polysaccharides, mainly — stay behind.

"Sometimes the crusts begin with green algae instead of cyanobacteria, often in places where the base soil is more acidic. Sometimes the two foundational phyla coexist, and sometimes a crust’s bedrock filament mat will shift from one to the other if soil pH shifts. Over time an entire swath of soil can become riddled with the filaments, and other organisms colonize them. Lichens are common crust inhabitants, as are free-living fungi, and the fungal hyphae from both add to the sturdiness of the crust. Mosses often join the cryptobiotic crust community, as do liverworts ..."