PARENT SESSION
Oral Session #59: Soil Ecology: Microbial and Invertebrate.
Presiding: M. Rillig
Wednesday, August 7. 8:00 AM to 11:30 AM. Palo Verde Room, Radisson.
Temporal variation in community composition and pigmentation of desert cyanobacterial soil crusts.
Bowker, Matthew*,1, Reed, Sasha2, Belnap, Jayne2, Phillips, Susan2, 1 Department of Biological Sciences, Flagstaff, AZ2 USGS-BRD, Canyonlands Field Station, Moab, UT
ABSTRACT- Summers on the Colorado Plateau (USA) are typified by harsh conditions such as high temperatures, brief soil hydration periods, and high UV and visible radiation. We investigated whether community composition and pigmention might vary in biological soil crusts as a result of such conditions. Representative surface cores were sampled on the ENE, WSW, and top microaspects of 20 individual soil crust pedicels at a single site in Canyonlands National Park, Utah, in spring and fall of 1999. Frequency of major cyanobacterial taxa and pigment concentrations were measured for each core. The frequency of major cyanobacterial taxa was lower in the fall compared to spring. The less-pigmented cyanobacterium Microcoleus vaginatus showed significant mortality when not in the presence of Nostoc spp. and Scytonema myochrous (both synthesizers of UV radiation-linked pigments) but exhibited little or no mortality when these species were abundant. We hypothesize that the sunscreen pigments produced by Nostoc and Scytonema in the surface of crusts protect other less-pigmented taxa. When fall and spring samples were compared, overall cyanobacterial frequency was lower in fall, while sunscreen and photosynthetic pigment concentrations were higher in fall. In the fall sample, most pigments associated with UV radiation or repair were at their highest concentrations on pedicel tops and WSW microaspects, and at their lowest concentrations on ENE microaspects. We suggest that differential pigment concentrations between microaspects are induced by varying UV radiation dosage at the soil surface on these different microaspects.
KEY WORDS: Biological soil crusts, UV radiation, Cyanobacteria, Pigments