Climate Variability and Landscape Fluxes

Climate Variability and Landscape Fluxes

This research task serves as a bridge between ORNL TES SFA components in manipulative experiments and fundamental process studies and those in modeling. Its overall goal is to develop a mechanistic understanding of ecosystem structural and functional responses to climate variability at different spatial and temporal scales and to transform such understanding to ecological, societal and modeling applications concerning impacts of various atmospheric stresses (e.g., droughts, heatwaves, unseasonable temperature changes).

This overall goal will be achieved by:
  • Providing coordinated, continuous, process-rich measurements from belowground to top of canopy and from leaf to landscape scales for process understanding and model testing
  • Developing improved and new process representations suitable for implementation in large-scale ESMs
  • Developing and testing ecologically and physiologically-based indicators and predictors of impacts of climate variability and extreme events that can contribute to the National Climate Change Indicator System
  • Conducting cross-scale/site syntheses of new advances, data sets and models to answer crucial science questions related to ecosystem structural and functional responses to climate variability and extreme events.

Major research components under this task include the following:

             1. The Missouri Ozark AmeriFlux (MOFLUX) Site

             2. The SPRUCE Mass and Energy Fluxes

             3. Integrated Research

The Missouri Ozark AmeriFlux (MOFLUX) Site

The MOFLUX site is part of the long-term, high quality core sites of the AmeriFlux network. It is located in the University of Missouri’s Baskett Wildlife Research and Education Area (BWREA, Lat. 38o44’39’’N, Long. 92o12’W), placed strategically within the geographically and ecologically distinct prairie-forest biome / precipitation transition in the central United States. MOFLUX operates a suite of meteorological, flux, ecological, physiological, and biometrical measurement systems that are either above or within the canopy, or on the forest floor, or in the soil. From its initiation in 2004, MOFLUX has played a key role in nearly all major Fluxnet and AmeriFlux network syntheses. The MOFLUX forest is the world’s strongest isoprene source that has ever been measured (Potosnak et al. 2014). MOFLUX has been crucial to the reformulation of the fundamental eddy covariance (EC) equation (Gu et al. 2012) and the development of novel EC theories (Gu et al. 2013). MOFLUX research has contributed to the improved understanding of photosynthetic carbon isotope discrimination (Gu and Sun 2014) and the importance of mesophyll diffusion for terrestrial carbon cycle (Sun et al. 2014).

The MOFLUX site characteristic and data are available from the AmeriFlux web site (http://ameriflux.ornl.gov/). Additional information is also available from the FLUXNET site (http://www.fluxnet.ornl.gov/fluxnet/sitepage.cfm?SITEID=967).

For FY 2016 to 2018, MOFLUX research will focus on:
  • Root dynamics and its relation to soil efflux and canopy functions
  • Spatial/temporal heterogeneity of soil moisture and its ecological impact
  • Leaf to canopy solar induced chlorophyll fluorescence measurements and modeling to partition EC measurements of net ecosystem exchange (NEE) of CO2 into gross primary production and ecosystem respiration.


The SPRUCE Mass and Energy Fluxes

Eddy covariance measurements at the SPRUCE site in northern Minnesota will include fluxes of CO2, methane, water vapor and sensible heat. Fluorescence measurements will be also made to provide multi-scale GPP estimates at SPRUCE. The primary objective is to collect ambient landscape-level flux observations for these variables for comparison to plot-level SPRUCE manipulations. Such measurements will produce temporally resolved measures for testing ecosystem models with a specific focus on the development of an efficacious CLM-Wetland model. An associated empirical objective is to quantify raised-bog peatland CH4 and CO2 fluxes and the relationships between them as the ecosystem responds to climate variability at hourly to inter-annual time scales.

Integrated Research

To move beyond an investigation of individual ecosystem components, measurements and process understanding will be integrated into broad system modeling frameworks in close collaboration with the TES SFA modeling efforts. Specifically, MOFLUX root observations will contribute to the development and validation of CLM root module. The partitioning of NEE into gross primary production and ecosystem respiration with joint fluorescence, EC and soil respiration measurements will be used to validate and improve CLM photosynthesis and ecosystem respiration modeling. Measurements of spatial variability in soil moisture will be made available to the ORNL’s ACME and PFLOTRAN teams for validating and improving subsurface flow and reactive transport model. These efforts will lead to a better integrative understanding of how dynamic environmental forcings such as precipitation regimes affect ecosystem C uptake, water use, surface energy balance, spatial/temporal heterogeneity of soil moisture, and other above- and below-ground biogeochemical processes.

References

Gu L & Sun Y (2014) Artefactual responses of mesophyll conductance to CO2 and irradiance estimated with the variable J and online isotope discrimination methods. Plant Cell & Environment 37: 1231-1249.

Gu, L., W.J. Massman, R. Leuning, S.G. Pallardy, T. Meyers, P.J. Hanson, J.S. Riggs, K.P. Hosman, B. Yang (2012) The fundamental equation of eddy covariance and its application in flux measurements. Agricultural and Forest Meteorology 152, 135-148.

Gu LH (2013) An eddy covariance theory of using O2 to CO2 exchange ratio to constrain measurements of net ecosystem exchange of any gas species. Agricultural and Forest Meteorology 176, 104-110.

Potosnak MJ, LeStourgeon L, Pallardy SG, Hosman KP, Gu LH, Karl T, Gerone C & Guenther AB (2014) Observed and modeled ecosystem isoprene fluxes from an oak-dominated temperate forest and the influence of drought stress. Atmospheric Environment 84: 314-322.

Sun Y, Gu L, Dickinson RE, Norby RJ, Pallardy SG, Hoffman FM (2014) Impact of mesophyll diffusion on estimated global land CO2 fertilization. Proceedings of the National Academy of Sciences of the United States of America, 15774–15779, doi: 10.1073/pnas.1418075111.