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Major Players in Microbiotic Crusts...

This is the major player in a lot of these crusts. It is Microcoleus vaginatus. It's a cyanobacterium or blue green alga. Microcoleus occurs in deserts worldwide. It actually occurs in soils worldwide, so even in Ohio we find these things. I don't know if they're actually all the same. We need to explore the genetic variability in what we call Microcoleus. They are characterized by having a whole bunch of trichomes or filaments of blue green algae in a common sheath. They have the same dimensions and same appearance worldwide, a very cosmopolitan species.


This is another very cosmopolitan species, Schizothrix calcicola. It is actually a much smaller organism. It is also very abundant. It is present in all deserts, but Microcoleus is in the cool desert dominant, while Schizothrix dominates in the hotter deserts.


Here's another cyanobacterium or blue green alga. The larger, clearish cells are the heterocysts. This is a Nostoc species. The significance of genera with heterocysts is that these are the cyanobacteria that are most responsible for nitrogen fixation. Thus, in the desert we have nitrogen fixers, and Nostoc is a key player in this process. Now, Nostoc is important not only as a free living cyanobacterium in the soil, it also occurs as a phycobiont in many of the lichens, so many of the lichens can fix nitrogen as well.


Here is another heterocystous species. This is a Tolypothrix and you can see a couple of heterocysts right in the middle of the filament. Another blue-green, Scytonema. I want to point out something here because Lynn Rothschild introduced it quite well. You can see the sheath is quite yellow. This contains the Scytonema that she was talking about. This is a UV screen, vital to these organisms because they really have to face the UV. In the desert sun, when sunlight comes down and hits them right on the surface of the soil, they are really being nailed by UV. The desert soil surface is a very extreme habitat with UV, temperature, and extreme desiccation. All these organisms must have adaptations in order to survive in this extreme environment. So those are all cyanobacteria. We have lots of different groups.


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