PARENT SESSION
Oral Session #25: Soil Ecology: Microbial and Invertebrate. Presiding: W. Parsons.
Tuesday, August 7, 2001. 8:00 AM to 12:00 PM. Hall of Ideas G.
The effects of microbiotic soil crust on soil moisture loss.
George, Dylan1, Roundy, Bruce2, St. Clair, Larry2, Johansen, Jeff3, Schaalje, Bruce2, Webb, Bruce2, 1 2 3
ABSTRACT- Microbiotic soil crusts play several important roles in many arid and semi-arid ecosystems around the world. However, their effects on soil hydrology are poorly understood. It has been speculated that crusts (1) improve soil moisture availability by 'sealing' the soil surface to water loss, or (2) diminish soil moisture by increasing the latent heat of a soil profile thereby increasing evaporation. In order to distinguish between these two opposing hypotheses, we analyzed moisture loss and temperature of soil profiles covered by different types of microbiotic soil crust (cyanobacteria, Psora decipiens, Placidium squamulosum) and a bare soil. We conducted experiments under growth chamber and field conditions. After watering to field capacity, crusted surface soils (1-3 cm deep) took as long or longer to decrease to -1.5 MPa water potential as bare soil in both the growth chamber and the field. In the growth chamber, soils covered by each of the crust types took longer to dry than bare soil, but, in the field, soils covered by cyanobacteria took longer than bare soils or those covered by the other crusts. Soil temperature was not different among the different crust types and bare soil in either experiment. This study did not support the hypothesis that crusts dry a soil profile more quickly by increasing the amount of energy available for evaporation. Rather our data suggested that crusts increase soil moisture availability by increasing water flux resistance, specifically at the soil surface. Past studies have overlooked the importance of species composition in determining different ecosystem processes, yet crust-specific effects were apparent in this study. This result emphasizes the importance of characterizing crust composition in future studies.
KEY WORDS: microbiotic crust, hydrology, available soil moisture