Kevin Tu University of California, Berkeley 510-642-1054 ktu@socrates. berkeley.edu
Tim Griffis University of Minnesota
Chun-Ta Lai University of Utah
Bill Riley Lawrence Berkeley National Lab
Nate McDowell Los Alamos National Labs
We describe the role that a network of stable isotope measurements of C and O in atmospheric CO2 and H2O play in addressing the science challenges of NEON, and specifically, how do the interactive effects of climate, land use, hydrology and environmental chemistry affect the carbon and water cycles of terrestrial ecosystems of the United States, in particular exchanges between ecosystems and the atmosphere, their response to long-term changes, and feedbacks to the climate system.
Understanding and forecasting fluxes of carbon and water requires robust techniques to partition the net fluxes made by eddy covariance into their process-level components, estimate the environmental sensitivities of the separate fluxes, and incorporate those sensitivities into forecasts using models.
Stable isotopes of C and O in CO2 (13C, 18O) and H2O (D, 18O) provide powerful constraint on different biological and physical processes as each imparts a process-specific isotopic signature on atmospheric CO2 or H2O. As a result, the combination of meteorological and stable isotope techniques has significantly advanced our understanding of land-atmosphere fluxes of carbon and water.
It is expected that the capacity of the isotope measurements to achieve the aforementioned results will in turn provide: 1) greater insight into the controls on 13CO2 discrimination processes and isotopic disequilibrium between photosynthetic uptake and respiratory losses associated with climate variation and land use change; 2) a mechanistic understanding of the physiological and ecological processes controlling gross leaf, root and microbial fluxes, including the importance of lags, pulses, acclimation, and functional and/or species diversity on ecosystem function; 4) separating the contribution of C3 and C4 plant types to ecosystem fluxes; 5) identification of source water depths and the role of rooting depth in plant and ecosystem response to climate variability; and 6) the ability to forecast future ecosystem-atmosphere carbon and water fluxes based on scenarios of external forcing (e.g. fossil fuel burning, land use change, atmospheric pollution), including prediction of feedbacks with the climate and ecological systems (e.g. succession, disturbance).
The science question addressed here is designed to complement and leverage the activities and design described in the “AmeriFlux Consortium for Continental Trends” RFI.