PARENT SESSION
Poster Session # 10: Soil Ecology.
Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Ecological contributions of hypolithic cryptobiotic soil crusts in hyperarid ecosystems.
Heckman, Katherine*,1, Anderson, Wendy1, Wait, Alexander2, 1 Drury University, Springfield, MO, USA2 Southwest Missouri State University, Springfield, MO, USA
ABSTRACT- The important role cryptobiotic soil crusts play in terrestrial ecosystems has only recently been recognized. In arid ecosystems, this role is amplified by the fact that soil crusts represent a large percentage of overall productivity. In such environments, where conditions at the soil surface are exceedingly harsh, crusts can be found living underneath semi-translucent rocks such as quartz. Very little is known about the ecological role of these hypolithic crusts in arid ecosystems, e.g., their impacts on soil, C-fixation, N-fixation, and contributions to other taxa, including plants and animals. We addressed these questions with a study of hypolithic crust communities on three hyperarid islands in the midriff region of the Gulf of California. Crusts were found in areas with inherently low soil N content, but were absent in soils with high N content (i.e. those with seabird guano enrichment). When present, crusts were found on 41% of quartz rocks, covering approximately 1.0% of the sampling area. Soils underneath encrusted rocks exhibited higher NO3 and organic content than soils unassociated with hypolithic crusts. Crusts were also found to alter soil properties such as pH, element concentrations, moisture content, and salinity. The hypolithic crusts in these communities also represent an integral part of the nitrogen cycle. The crusts were found to have 15N isotope ratios between 0 and 1.5, indicating a high level of N fixation. We hypothesized that this fixed N would be released into the surrounding soils where it would be taken up by annual plants growing within a certain proximity. Stable isotopes confirmed soil crusts as the dominant source of N for surrounding plants and soil. Though hypolithic soil crusts remain a somewhat obscure and unapparent part of the landscape, further exploration of their relative importance will inspire appreciation of the fundamental part they play in hyperarid ecosystems.
Key words: deserts, cyanobacteria, nitrogen fixation, nitrogen isotopes