PARENT SESSION
Contributed Oral Session 89: Soil Ecology: Plant - Soil Relationships
Wednesday, August 10, 8:00 AM - 11:30 AM, Meeting Room 524 B, Level 5, Palais des congrès de Montréal
Landscape level effects of increased nitrogen deposition, summer precipitation and soil disturbance on surficial nitrogen and phosphorous dynamics.
Zimpfer, Jeff*,1, Wagner, Diane2, Newingham, Beth3, Smith, Stanley3, 1 University of Hawai'i Sea Grant College Program, Honolulu, Hawai'i, USA2 University of Alaska Fairbanks, Fairbanks, Alaska, USA3 University of Nevada, Las Vegas, Las Vegas, Nevada, USA
ABSTRACT- Biological soil crusts (lichen, moss, fungi, cyanobacteria and algae) play a critical role in the Mojave Desert by reducing soil erosion and increasing phosphorous and nitrogen availability. Climate and land use changes are likely to affect the integrity and physiological processes of crusts, and thus the availability and forms of nitrogen and phosphorous. At the Mojave Global Change Facility in Nevada, we increased rates of nitrogen deposition (10 and 40 kg NO3-N ha-1 y-1), summer precipitation (7.5 cm y-1), and soil disturbance (trampling) on 48-14 x 14 m plots. Treatments were initiated in 2001. In June 2002, following a very dry winter and spring, and April 2004 following a "wet" winter and spring, we randomly collected soil cores (1 cm x 3 cm dia.) from control, 10N, 40N, irrigated and disturbed plots. In the lab we measured rates of N-fixation via acetylene reduction (AR) and chlorophyll a (chl a) content. We also determined organic matter, plant available phosphorous, ammonia and nitrate of the soil cores. There were no statistical differences in rates of N-fixation or chl a content for samples collected in the summer of 2002. However, for samples collected in late spring of 2004, 10N plots had the highest AR (P < 0.05) rates. Lower rates of AR were found in 40N, summer irrigated, and soil disturbance plots (P < 0.01, P < 0.05, and P < 0.001, respectively). In 2004, 40N and disturbed plots had significantly less chl a than controls (P < 0.05, P < 0.001, respectively). Irrigation decreased surface soil organic matter and increased both soil and mineral N. Disturbance had no significant effect on soil chemistry, and N addition increased both NO3-N and NH4-N, but had no effect on soil organic matter. Our results suggest that added N, soil disturbance and changes in precipitation regimes significantly alter biological soil crust N and P dynamics, as well as crust physiology.
Key words: biotic crusts, Mojave Desert, global change, nitrogen fixation