PARENT SESSION
Oral Session #44: Global Change and Climate Change.
Presiding: C. Wessman
Tuesday, August 6. 1:00 PM to 4:45 PM. Grand Ballroom West, Radisson.

Soil nitrate and phosphate availability under simulated global changes in a California annual grassland ecosystem.

Kerr, Amber^*,1, Cleland, Elsa^1,2, Shaw, Rebecca², Field, Christopher^1,2, ¹ Dept. of Biological Sciences, Stanford University, Stanford, CA² Dept. of Global Ecology, Stanford, CA

ABSTRACT- As atmospheric carbon dioxide (CO₂) concentrations rise, increasing attention is focusing on the potential for terrestrial ecosystems to take up excess carbon into plants and soils. Soil nutrient availability is expected to constrain plant production responses to elevated CO₂, and nutrient availability may also be changed by other global changes. This study aimed to non-destructively measure plant-available nitrate and phosphate under simulated global changes. Since 1998, in a California annual grassland, the Jasper Ridge Global Change Experiment (JRGCE) has simulated four drivers of global change; increased atmospheric CO₂, temperature, nitrogen deposition, and precipitation. The design is fully factorial, allowing detailed analysis of ecosystem response to interacting drivers of global change (16 treatments, 8 replicates, N=128, significance level p<0.05). Nitrate and phosphate were measured using ion-exchange resins placed in nylon bags at 30 cm depth. Bags were left in the ground for seven days at a time, and measurements were made over the course of the growing season from November to May. Nitrogen deposition strongly increased nitrate availability, but decreased phosphate availability. Elevated CO₂, increased precipitation, and warming all decreased nitrate availability. Increased precipitation and elevated CO₂ also tended to decrease phosphate availability (non-significant trend). The results of this study show that nutrient availability is altered in complex ways by interacting global changes; with the exception of nitrogen deposition, nutrient availability generally decreased under simulated global changes.

KEY WORDS: global change, nutrient availability, nitrogen, phosphorous