title: Diurnal, seasonal and interannual variability of carbon isotope discrimination at the canopy level in response to environmental factors in a boreal forest ecosystem.
abstract: Accurate estimation of temporal and spatial variations in photosynthetic discrimination of 13C is critical to carbon cycle research. In this study, a combined ecosystem-boundary layer isotope model, which was satisfactorily validated against intensive campaign data, was used to explore the temporal variability of carbon discrimination in response to environmental driving factors in a boreal ecosystem in the vicinity of Fraserdale Tower, Ontario, Canada (49 degrees 52'30''N, 81 degrees 34'12''W). A 14 year (1990-1996 and 1998-2004) hourly CO2 concentration and meteorological record measured on this tower was used for this purpose. The 14 year mean yearly diurnal amplitude of canopy-level discrimination Delta(canopy) was computed to be 2.8 +/- 0.5 per thousand, and the overall diurnal cycle showed that the greatest Delta(canopy) values occurred at dawn and dusk, while the minima generally appeared in mid-afternoon. The average annual Delta(canopy) varied from 18.3 to 19.7 per thousand with the 14 year average of 19 +/- 0.4 per thousand. The overall seasonality of Delta(canopy) showed a gradually increasing trend from leaf emergence in May-September and with a slight decrease at the end of the growing season in October. Delta(canopy) was negatively correlated to vapour pressure deficit and air temperature across hourly to decadal timescales. A strong climatic control on stomatal regulation of ecosystem isotope discrimination was found in this study.
authors.affiliation: Department of Geography and Program in Planning, University of Toronto, Ontario, Canada. baozhang.chen@ubc.ca
authors.forename: Baozhang
authors.initials: B
authors.lastname: Chen
authors.forename: Jing M
authors.initials: JM
authors.lastname: Chen
mesh_terms: D002244:Carbon / Q000737:chemistry* / Q000378:metabolism*; D002247:Carbon Isotopes; D002940:Circadian Rhythm; D032462:Cycadopsida / Q000502:physiology; D017753:Ecosystem; D016014:Linear Models; D009864:Ontario; D010788:Photosynthesis; D018515:Plant Leaves / Q000502:physiology*; D012621:Seasons; D014197:Trees / Q000502:physiology*
chemical_list: D002247:Carbon Isotopes; D002244:Carbon