Diurnal centroid of ecosystem energy and carbon fluxes at FLUXNET sites.

[1] Data from a network of eddy covariance stations in Europe and North America (FLUXNET) were analyzed to examine the diurnal patterns of surface energy and carbon fluxes during the summer period across a range of ecosystems and climates. Diurnal trends were quantified by assessing the time of day surface fluxes and meteorological variable reached peak values, using the “diurnal centroid” method; the diurnal centroid enabled us to discern whether the peak activity of the variable of interest is weighted more toward the morning or afternoon. In this paper, diurnal centroid estimates were used to diagnose which atmospheric and physiological processes controlled carbon dioxide, water vapor, and sensible heat fluxes across different ecosystems and climates. Sensitivity tests suggested that the diurnal centroids for latent (LE) and sensible (H) heat flux depend on atmospheric resistance, static stability in the free atmosphere, stomatal response to vapor pressure deficit, and advection. With respect to diurnal trends of surface energy fluxes at FLUXNET sites, maximum LE occurred later in the day relative to H at most tall forests with continental climates. The lag between LE and H was reduced or reversed at sites that were influenced by advection or by afternoon stomatal closure. The time of peak carbon uptake of temperate forests occurred earlier relative to the temporal peak of photosynthetically active radiation, as compared to boreal forests. The timing of this peak occurred earlier during periods with low soil water content, as it did during the summer in Mediterranean climates. In this case, the diurnal centroid for the CO2 flux was influenced by the response of respiration and photosynthesis to increasing afternoon temperature and by afternoon stomatal closure.

[1]  P. Berbigier,et al.  Transpiration of a 64-year old maritime pine stand in Portugal , 1996, Oecologia.

[2]  P. Berbigier,et al.  Transpiration of a 64-year-old maritime pine stand in Portugal , 1996, Oecologia.

[3]  J. Tenhunen,et al.  Above- and below-ground environmental influences on leaf conductance ofCeanothus thyrsiflorus growing in a chaparral environment: drought response and the role of abscisic acid , 1994, Oecologia.

[4]  W. Oechel,et al.  Energy partitioning between latent and sensible heat flux during the warm season at FLUXNET sites , 2002 .

[5]  C. Osmond,et al.  Department of Plant Biology , 2002 .

[6]  W. Oechel,et al.  FLUXNET: A New Tool to Study the Temporal and Spatial Variability of Ecosystem-Scale Carbon Dioxide, Water Vapor, and Energy Flux Densities , 2001 .

[7]  Andrew E. Suyker,et al.  Gap filling strategies for long term energy flux data sets , 2001 .

[8]  A. Goldstein,et al.  Carbon dioxide and water vapor exchange by young and old ponderosa pine ecosystems during a dry summer. , 2001, Tree physiology.

[9]  Tilden P. Meyers,et al.  A comparison of summertime water and CO2 fluxes over rangeland for well watered and drought conditions , 2001 .

[10]  Michael R. Raupach,et al.  Equilibrium Evaporation and the Convective Boundary Layer , 2000, Boundary-Layer Meteorology.

[11]  Hans Peter Schmid,et al.  Measurements of CO2 and energy fluxes over a mixed hardwood forest in the mid-western United States , 2000 .

[12]  Dennis D. Baldocchi,et al.  Spatial and seasonal variability of photosynthetic parameters and their relationship to leaf nitrogen in a deciduous forest. , 2000, Tree physiology.

[13]  Ü. Rannik,et al.  Respiration as the main determinant of carbon balance in European forests , 2000, Nature.

[14]  Ye Qi,et al.  Effects of climate variability on the carbon dioxide, water, and sensible heat fluxes above a ponderosa pine plantation in the Sierra Nevada (CA) , 2000 .

[15]  Dennis D. Baldocchi,et al.  Seasonal and interannual variability of energy fluxes over a broadleaved temperate deciduous forest in North America , 2000 .

[16]  Ü. Rannik,et al.  Estimates of the annual net carbon and water exchange of forests: the EUROFLUX methodology , 2000 .

[17]  Hans Peter Schmid,et al.  Measurements of CO 2 and energy fluxes over a mixed hardwood forest in the mid-western United States , 2000 .

[18]  T. A. Black,et al.  Responses of net ecosystem exchanges of carbon dioxide to changes in cloudiness: Results from two North American deciduous forests , 1999 .

[19]  Toby N. Carlson,et al.  Feedback significantly influences the simulated effect of CO2 on seasonal evapotranspiration from two agricultural species , 1999 .

[20]  B. Law,et al.  Carbon and water vapor exchange of an open-canopied ponderosa pine ecosystem , 1999 .

[21]  D. Whitehead.  Regulation of stomatal conductance and transpiration in forest canopies. , 1998, Tree physiology.

[22]  Michael R. Raupach,et al.  Influences of local feedbacks on land–air exchanges of energy and carbon , 1998 .

[23]  M. G. Ryan,et al.  Comparing nocturnal eddy covariance measurements to estimates of ecosystem respiration made by scaling chamber measurements at six coniferous boreal sites , 1997 .

[24]  D. Lenschow,et al.  Role of entrainment in surface-atmosphere interactions over the , 1997 .

[25]  S. Wofsy,et al.  Physiological responses of a black spruce forest to weather , 1997 .

[26]  J. Lhomme.  An examination of the Priestley‐Taylor equation using a convective boundary layer model , 1997 .

[27]  Dennis D. Baldocchi,et al.  Measuring and modelling carbon dioxide and water vapour exchange over a temperate broad‐leaved forest during the 1995 summer drought , 1997 .

[28]  A. Mäkelä,et al.  Optimal Control of Gas Exchange during Drought: Theoretical Analysis , 1996 .

[29]  P. Hanson,et al.  Stem respiration in a closed-canopy upland oak forest. , 1996, Tree physiology.

[30]  D. I. Cooper,et al.  Evaporation and the development of the local boundary layer over an irrigated surface in an arid region , 1996 .

[31]  C. Field,et al.  Ecosystem gas exchange in a California grassland : seasonal patterns and implications for scaling , 1995 .

[32]  R. Leuning.  A critical appraisal of a combined stomatal‐photosynthesis model for C3 plants , 1995 .

[33]  Relation between equilbrium evaporation and the saturation pressure budget , 1994 .

[34]  Jack A. Morgan,et al.  Consequences of growth at two carbon dioxide concentrations and two temperatures for leaf gas exchange in Pascopyrum smithii (C3) and Bouteloua gracilis (C4) , 1994 .

[35]  D. Baldocchi.  A comparative study of mass and energy exchange rates over a closed C3 (wheat) and an open C4 (corn) crop: II. CO2 exchange and water use efficiency , 1994 .

[36]  Stephanie A. Bohlman,et al.  Seasonal and topographic patterns of forest floor CO(2) efflux from an upland oak forest. , 1993, Tree physiology.

[37]  N. Turner.  Measurement and influence of environmental and plant factors on stomatal conductance in the field , 1991 .

[38]  D. M. Gates,et al.  Gas exchange in Quercus rubra (northern red oak) during a drought: analysis of relations among photosynthesis, transpiration, and leaf conductance. , 1990, Tree Physiology.

[39]  Toby N. Carlson,et al.  A stomatal resistance model illustrating plant vs. external control of transpiration , 1990 .

[40]  A. Dolman,et al.  Stomatal behaviour in an oak canopy , 1988 .

[41]  J. Wyngaard.  A Physical Mechanism for the Asymmetry in Top-Down and Bottom-Up Diffusion. , 1987 .

[42]  B. Loveys,et al.  DIURNAL CHANGES IN THE PHOTOSYNTHESIS OF FIELD-GROWN GRAPE VINES. , 1987, The New phytologist.

[43]  K. McNaughton,et al.  A mixed-layer model for regional evaporation , 1986 .

[44]  K. G. McNaughton,et al.  Stomatal Control of Transpiration: Scaling Up from Leaf to Region , 1986 .

[45]  A. Lindroth.  Canopy Conductance of Coniferous Forests Related to Climate , 1985 .

[46]  A. E. Hall,et al.  Stomatal Responses, Water Loss and CO2 Assimilation Rates of Plants in Contrasting Environments , 1982 .

[47]  I. R. Cowan.  Regulation of Water Use in Relation to Carbon Gain in Higher Plants , 1982 .

[48]  H. Tennekes,et al.  Basic entrainment equations for the atmospheric boundary layer , 1981 .

[49]  J. Berry,et al.  Photosynthetic Response and Adaptation to Temperature in Higher Plants , 1980 .

[50]  S. Running,et al.  Temporal and Spatial Variations in the Water Status of Forest Trees , 1978 .

[51]  S. Verma,et al.  Extreme Evapotranspiration by Irrigated Alfalfa: A Consequence of the 1976 Midwestern Drought , 1978 .

[52]  Norman J. Rosenberg,et al.  Local and Regional Components of Sensible Heat Advection , 1978 .

[53]  P. Jarvis.  The Interpretation of the Variations in Leaf Water Potential and Stomatal Conductance Found in Canopies in the Field , 1976 .

[54]  P. G. Jarvis,et al.  Photosynthesis in Sitka Spruce (Picea sitchensis (Bong.) Carr.): VI. Response of Stomata to Temperature , 1975 .

[55]  H. Tennekes,et al.  A Model for the Dynamics of the Inversion Above a Convective Boundary Layer , 1973 .