Biological Soil Crusts of Joshua Tree National Park

Biology x412.28 (1 unit)

Nicole Pietrasiak, M.S., and Ph.D. Candidate, Graduate

Teaching Assistant, UC Riverside

B.S. Biology, John Carroll University, University Heights, Ohio


I.                Definitions

a.     Biological soil crust (aka cryptobiotic crust, cyanobacteria, blue-green algae) means the “communities of cyanobacteria, green algae, lichens, mosses, liverworts, and microorganisms that colonize the surface of bare soil…Crusts hold the soil in place and protect underlying sediments from erosion.  They pioneer soil development on bare inorganic sediments, absorbing water and enriching the surface with nutrients and organic matter…the first stage in the natural revegetation of barren ground…They are among the oldest and most primitive life forms on earth….”

b.     Bacteria, unicellular microorganisms (the proper study of bacteriology or microbiology) “microscopic, single-celled organisms”

                                                    i.     Cyanobacteria: “photosynthetic bacteria formerly called blue-green algae, their growth forms tend to be filamentous. “

c.      Fungi: “nonphotosynthetic multicellular organisms that are either saprophytic or parasitic.”

d.     Hyphae: “single strands of a fungus.”

e.     Lichen: “a composite plant consisting of fungi living symbiotically with algae or cyanobacteria.”

f.      Liverworts and mosses: “nonvascular plants of small stature, the two are similar with the exception of reproductive methods.”

g.     Rhizines/rhizoids: “root-like structures of lichens and mosses respectively, they are used for attachment.”

h.     Sheaths:external coating formed by some filamentous cyanobacteria, those discussed in the article are formed from polysaccharides.”

i.       Algae: “nonvascular photosynthetic plant-like organisms, they are informally divided into groups by their dominant pigments (i.e., green, brown, red, etc.).”

                                                    i.     algae species

1.     10,000 living diatom species

2.     8,000 species of algae

                                                  ii.     1,500 of blue-green algae (i.e., filamentous cyanobacteria)

1.     Anabaena, can fix atmospheric nitrogen (symbiotic relationship with ???)

                                                iii.     Red (i.e., Rhodophyta)

                                                iv.     7,000 species of green algae (most have a single nucleus; chlorophyll to capture light energy to manufacture sugars) 

                                                  v.     Brown (i.e., Phaeophyceae)

j.       Circadian rhythms (KaiC phosphorylation cycle


II.              Environment

a.     Abiotic (minerals in soil)

b.     Inter-species relationships

                                                    i.     Neither profits, no relationship (neutralism)

                                                  ii.     One profits, one doesn’t care (commensalism)

                                                                                                                i.     Birds nesting in a tree

                                                                                                              ii.     Cattle egret in Costa Rica

                                                iii.     Both profit (mutualism)

                                                                                                                i.     Yucca moth/yucca (total co-dependency)

                                                iv.     One profits, other doesn’t (parasitism)

                                                                                                                i.     Mistletoe

                                                  v.     One profits, killing the other (predatorism)



Lorena B. Moore, “Cryptobiotic Crust in the Sonoran Desert (updated 6.6.07)”

An Introduction to Biological Soil Crusts (updated: April 24, 2006)


1)     A. Herrero and E. Flores, editors. The Cyanobacteria: Molecular Biology, Genomics and Evolution.  Norwich: Caister Academic Press, 2008.

ABSTRACT: Cyanobacteria are a fascinating and versatile group of bacteria of immense biological importance. Thought to be amongst the first organisms to colonize the earth, these bacteria are the photosynthetic ancestors of chloroplasts in eukaryotes such as plants and algae. In addition they can fix nitrogen, survive in very hostile environments (e.g. down to -60°C), are symbiotic, have circadian rhythms, exhibit gliding mobility, and can differentiate into specialized cell types called heterocysts. This makes them ideal model systems for studying fundamental processes such as nitrogen fixation and photosynthesis. In addition cyanobacteria produce an array of bioactive compounds, some of which could become novel antimicrobial agents, anti-cancer drugs, UV protectants etc. The amazing versatility of cyanobacteria has attracted huge scientific interest in recent years. Given that 24 genomes sequences have been completed and many more projects are currently underway, the point has been reached where there is an urgent need to summarize and review the current molecular biology, genomics, and evolution of these important organisms.


This volume brings together the expertise and enthusiasm of an international panel of leading cyanobacterial researchers to provide a state-of-the art overview of the field. Topics covered include: evolution, comparative genomics, gene transfer, molecular ecology and environmental genomics, stress responses, bioactive compounds, circadian clock, structure of the photosynthetic apparatus, membrane systems, carbon acquisition, nitrogen assimilation and C/N balance sensing and much more. Essential for anyone with an interest in cyanobacteria, bacterial photosynthesis, bacterial nitrogen fixation, and symbiosis.  See chapter details at link above.



2)     Nicole Pietrasiak, Jeffrey R. Johansen, and Tasha La Doux, “Biogeography of Microbiotic Crusts in Joshua Tree National Park” ESA/SER Jointing Meeting, August 2007.

ABSTRACT: All wilderness segments within the boundaries of Joshua Tree National Park were surveyed for frequency and cover of microbiotic soil crusts.  Areas within both the Mojave Desert and Colorado Desert were examined.  A total of eight vegetation community types were sampled.  In order of greatest sample representation, these community types were: Sonoran Creosote Bush Scrub, Mojave Creosote Bush Scrub, Blackbrush Scrub, Mojave Pinyon-Juniper Woodland, Mojave Mixed Woody Scrub, Mojave Mixed Steppe, Stabilized Sand Dunes, Sonoran Mixed Woody and Succulent Scrub.  A total of 75 research sites were established in the summer of 2006.  At all sites, 100 1.0 m2 frequency plots and 250 cover points were scored for shrub vegetation (by species), perennial grass and forbs, cacti, annuals (cover only), rock, and several crust categories (algal, lichen, moss, mixed crust).  

            Crust cover was generally low in most areas of the park in comparison to crust cover in other arid lands of the western United States.  Cover for total microbiotic crust was on average only 13.1%, with most of that cover attributable to algal crust (11.4%).  The remaining cover was due to lichens.  Only one site of the 75 had any detectable moss cover.  The vegetation zones with highest crust cover were Mojave Creosote Bush Scrub (18.7%), Sonoran Creosote Bush Scrub (14.4%), and Mojave Mixed Woody Scrub (9.9%).  All other vegetation zones had less than 6% average crust cover.  There was a weak correlation between the soil stability index and crust cover (R2=0.41).

3)     Barren Deserts Can Host Complex Ecosystems” (December 2014)



NOTE: Quotations in the definition section come from the “Glossary” at (accessed 30 September 2009).