PARENT SESSION
Oral Session # 19: Biogeochemistry II: Grasslands.
Presiding: JT Lennon
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 105.
Spatial and temporal variation in islands of fertility in a Sonoran Desert landscape.
Schade, John1, Hobbie, Sarah2, Sponseller, Ryan1, Collins, Scott3, 1 Arizona State University, Tempe, AZ2 University of Minnesota, St. Paul, MN3 University of New Mexico, Albuquerque, NM
ABSTRACT- The influence of canopy trees and shrubs on soil nutrient cycling and understory plants is complex and context-dependent. Canopy plants can exert positive, negative or neutral effects on nutrient cycling rates and production, composition, diversity and nutrient content of understory plant communities, depending on local environmental conditions and position in the landscape. We studied spatial and temporal variation in the influence of mesquite (Prosopis velutina) on soil moisture and nitrogen cycling rates, and understory vegetation along a topographic gradient in the Sonoran Desert. We found significant increases in both soil moisture and N along the gradient from desert to riparian zone. In addition, mesquite canopies had positive effects, relative to open areas, on soil moisture in the desert, and soil N availability, potential N mineralization rates and microbial biomass N in both desert and intermediate terrace, particularly during wet months. Biomass of understory vegetation was highest and species richness was lowest in the riparian zone. Canopies had a positive effect on biomass in both desert and terrace, and a negative effect on species richness in the terrace. The effect of the canopy depended on landscape position, with desert canopies more strongly influencing soil moisture and biomass and terrace canopies more strongly influencing soil N and species richness. Individual species distributions suggested interspecific variation in response to water- vs. N-availability strongly influences species composition at both patch and landscape position levels.
Key words: islands of fertility, landscape position, nitrogen cycling, canopy-understory interactions