HR: 1340h
AN: B43B-1175 INVITED    [Abstracts]
TI: Ecosystem Responses in the Jasper Ridge Global Change Experiment Over Seven Years
AU: * Gurwick, N P
EM: ngurwick@globalecology.stanford.edu
AF: Carnegie Institution, Dept of Global Ecology 260 Panama Street, Stanford, CA 94305, United States
AU: Field, C B
EM: cfield@globalecology.stanford.edu
AF: Carnegie Institution, Dept of Global Ecology 260 Panama Street, Stanford, CA 94305, United States
AU: Field, C B
EM: cfield@globalecology.stanford.edu
AF: Jasper Ridge Biological Preserve, Stanford University, Stanford, CA 94305, United States
AU: Field, C B
EM: cfield@globalecology.stanford.edu
AF: Stanford University, Dept of Biological Sciences Herrin Labs, Stanford, CA 94305, United States
AU: Chiariello, N
EM: nonajrbp@stanford.edu
AF: Jasper Ridge Biological Preserve, Stanford University, Stanford, CA 94305, United States
AU: Vitousek, P M
EM: vitousek@stanford.edu
AF: Stanford University, Dept of Biological Sciences Herrin Labs, Stanford, CA 94305, United States
AB: Field plots within a California grassland at Jasper Ridge, USA, have been exposed for 9 years to enhanced levels of CO2, nitrogen, heat, and precipitation, singly and in all possible combinations. We here report an updated analysis of major trends in NPP response, based on an analysis of data collected through 2006. First, as reported in earlier syntheses of NPP response at the JRGCE, NPP responded most strongly and consistently to enhanced N deposition. However, the magnitude of this response peaked in 2003 and had been markedly less pronounced since then. Second, all statistically significant effects emerged as interactions with year, highlighting the dependence of ecosystem responses to global change factors on temporal variation in uncontrolled drivers. Third, the influence of enhanced CO2 on NPP varied regularly across years, and correlated strongly with annual precipitation (R2=0.89, p<0.05). Contrary to expectations, enriched CO2 concentrations diminished NPP in dry years and enhanced NPP in wet years. Two observations point to the seasonal pattern of precipitation (vs. total amount) as mediating the ecosystem response to interactions among global change factors. First, although the effect of CO2 varied regularly with annual precipitation, the interaction of the CO2 and precipitation treatments did not produce a parallel result. The enhanced precipitation treatment in the JRGCE adds 50% to each rain event and adds two rain events to the end of the growing season but does not shift the pattern of rainfall during the growing season. Second, enhanced CO2 appears to diminish the positive effect of N deposition on NPP, contrary to a traditional model of co-limitation by C and N, but only in years with minimal precipitation during March.
UR: http://globalecology.stanford.edu/DGE/Dukes/JRGCE/home.html
DE: 0428 Carbon cycling (4806)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 1630 Impacts of global change (1225)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting