Landscape-level (Eddy Covariance) Measurement of CO 2 and Other Fluxes Measuring Components of Solar Radiation Close-up of Eddy Covariance Flux Sensors Tower Flux Measurement and Analysis Verma/IndoFlux/IndoFlux_July 2006

Outline Background information/ methodology Flux magnitudes: seasonal/ interannual variations Controlling variables Comments

Objectives Quantify CO 2 exchange in major ecosystems: seasonal and interannual variability Improve our basic understanding of biophysical processes that govern CO 2 exchange in these ecosystems Test and improve terrestrial biosphere models of CO 2, water, and energy exchange

Landscape Level Carbon Dioxide Flux (uptake and release) Plant photosynthesis Above ground productivity Root and rhizosphere respiration Partitioning of Carbon in Agroecosystems Soil respiration Plant respiration Microbial respiration Root exudates Root productivity Organic matter decomposition

Methodology: Eddy Covariance Fluxes of CO 2, Water Vapor, and Energy: Continuous Measurements Long-term Ecosystem scale/landscape level

Mead, Nebraska

Primary Measurements -Fluxes of CO 2, water vapor, sensible heat & momentum -Mean wind speed, air temperature, humidity and CO 2 concentration -Wind direction -Soil heat flux & soil temperature -Radiation:  Net radiation  Short wave radiation (incoming & reflected)  PAR (incoming & reflected) -Light interception -Atmospheric pressure -Precipitation Supporting Measurements -Soil moisture -Leaf area index, canopy height, biomass -Leaf nitrogen content Measurements Data Submission

Tower Eddy Covariance CO 2 Flux Measurements: Net Ecosystem Exchange (NEE) Mead, Nebraska

Daytime CO 2 Uptake and Night Emissions Ecosystem Peak daytime CO 2 uptake (mg m -2 s -1 ) Peak night CO 2 emission (mg m -2 s -1 ) Leaf Area Index (LAI) Irrigated maize2.8 – – – 6.0 Rainfed maize – Irrigated soybean Rainfed soybean Grassland (tallgrass prairie) – Temperate forest –

Re day = NEE night * Q 10 (T a,day - T a,night )/10 GPP = NEE - Re Ecosystem Respiration (Re) and Gross Primary Productivity (GPP)

Annually Integrated NEE (g C m -2 y -1 ) Maize, NE300 to 500 (Verma et al., 2005) Harvard Forest, MA200 (Barford et al., 2003) Howland Forest, ME174 (Hollinger et al., 2004) Univ. of Michigan Biological St80 to 170 (Schmid et al., 2003) Wind River, WA-50 to 200 (Pers. Comm.) Douglas Fir, B.C.270 to 420 (Morgenstern et al., 2004) Tallgrass Prairie, OK50 to 275 (Suyker et al., 2003) Northern Temperate Grassland, Alberta -18 to 20 (Flanagan et al., 2002) Mediterranean, Annual Grassland, CA -30 to 130 (Xu and Baldocchi, 2003) Soybean, NE-10 to -75 (Verma et al., 2005)

Incoming PAR (  mol m -2 s ) NEE (mg m -2 s ) June 13-19: V6-V7: 0.4<LAI<1.3 July 4-10: V11-V12: 4.4<LAI<5.6 July 18-24: V19-VT: 6.2<LAI<6.3 Aug 29-Sept 4: R5: 3.7<LAI<4.3 Daytime CO 2 Flux Irrigated Maize

Night CO 2 Flux

Tallgrass Prairie, Manhattan, KS, 1987

Energy Partitioning Daytime

Energy Partitioning Shidler, Oklahoma

Tallgrass Prairie, Manhattan, KS, 1987

Checks and Balances Data Quality Control –Foken and Wichura, 1996, Agric. For. Meteorol., 78, –Aubinet et al., 2000, Advances in Ecol. Res., 30, Energy Budget Closure: LE + H vs. Rn + G NEE – Biomass Relationship

Day Night NEE day NEE night RgRg RrRr RcRc Daily net gain of CO 2 by crop RgRg RrRr RcRc Gain of CO 2 by crop during day = NEE day – R g day DD DD = Net canopy photosynthesis in 24 hours = ( NEE day + NEE night ) – ( R g day + R g night )  D NN = Daily NEE + Daily R g Loss of CO 2 by crop at night =R c + R r = NEE night – R g night NN NN NN DD NN = ( NEE day – R g day ) + ( NEE night – R g night ) DD DD NN NN NN R c + R r + R g = NEE night (Biscoe et al; J. Applied Ecology, 12, ) NEE-Biomass Relationship

Daily net gain of CO 2 by crop =  Daily NEE  +  Daily R g  (Biscoe et al., 1975, J. Applied Ecology, 12, ) NEE = Net ecosystem CO 2 exchange R g = Respiration by soil organisms

Estimating Microbial Respiration (R g ) Soil surface CO 2 flux measurements (F s ) –Two different kinds of chambers: Model LI-6200, Li-Cor, Lincoln, NE Hutchinson & Mosier (1981) type chamber –Used data from field measurements of maize soil respiration in root excluded and non-root excluded soil to estimate R g Night NEE data –Adjusted for plant respiration based on leaf gas exchange measurements –Adjusted for night/day temperatures –Applied measurements of root-excluded vs. non-root excluded soil to estimate R g as mentioned above

Challenges Insufficient mixing at night Filling in data gaps Complex terrain

N 2 O and CH 4 Fluxes