PARENT SESSION
Oral Session #68: Nutrient Cycling. Presiding: D. Johnson.
Thursday, August 9, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.
C:N:P stoichiometry of soil, plants, and invertebrates along a moisture gradient in the Sonoran Desert.
Schade, John1, Elser, James1, Fagan, William1, Hobbie, Sarah2, 1 2
ABSTRACT- Studies of planktonic food webs have shown that imbalances in C:N:P stoichiometry of primary producers and consumers strongly influence trophic dynamics and consumer-driven nutrient cycling. New research has begun to extend the study of such stoichiometric relationships in terrestrial ecosystems. In this project, we describe temporal and spatial variation in soil nutrient availability and C:N:P in plants and insects along a moisture gradient in the Sonoran Desert. We measured nutrient availability using ion-exchange resins, and sampled foliage and insects from dominant plant species in 4 zones of a watershed in central Arizona in May and September 2000. Zones ranged from riparian through wet and dry mesquite (Prosopis sp.) woodlands to desert scrub. Both nitrogen and phosphorous availability and N:P in soils were higher in September than May. Small-scale spatial variation tended to be higher within desert scrub and dry mesquite plots than in riparian plots. Overall, spatial differences were small relative to temporal changes. Elemental content of plants in desert and riparian plots changed little over time, but C:N increased and N:P decreased in mesquite plots. This may be due to a strong response of N-fixing mesquite to changes in P availability, coupled with a weak response to the change in N availability. Both C:P and N:P in insect bodies increased in plots on the dry end of the gradient between May and September, with little change in riparian plots.
KEY WORDS: stoichiometry, nitrogen and phosphorous availability, desert moisture gradient, mesquite