At the leaf scale, it is a long-held assumption that stomata close at night in the absence of light, causing transpiration to decrease to zero. Energy balance models and evapotranspiration equations often rely on net radiation as an upper bound, and some models reduce evapotranspiration to zero at night when there is no solar radiation…. More

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Temperate deciduous forests exhibit dramatic seasonal changes in surface exchange properties following on the seasonal changes in leaf area index. Nearly continuous measurements of turbulent and radiative fluxes above and below the canopy of a red oak forest in central Massachusetts have been ongoing since the summer of 1991. Several seasonal trends are obvious. Global… More

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Carbon flux in arid and semiarid area shrublands, especially in old-growth shrub ecosystems, has been rarely studied using eddy covariance techniques. In this study, eddy covariance measurements over a 100-year old-growth chamise-dominated chaparral shrub ecosystem were conducted for 7 years from 1996 to 2003. A carbon sink, from −96 to −155 g C m−2 yr−1, was determined under normal… More

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Filtering methods based on morphological operations have been developed in some previous studies. The biggest challenge for these methods is how to keep the terrain features unchanged while using large window sizes for the morphological opening. Zhang et al. (2003) tried to achieve this goal, but their method required the assumption that the slope is… More

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Field experiments were conducted to determine optimal time during the day for N2O flux determination and to evaluate the effects of wheel traffic and soil parameters on N2O fluxes following urea ammonium nitrate (UAN) injection and summer UAN fertigations. The experiments were located on silty clay loam soils under no-till irrigated continuous corn of eastern… More

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A long-term flux measurement station has been established in a 74-year-old mixedwood forest ecosystem, located approximately 80 km west of Timmins in northern Ontario, as part of the Fluxnet-Canada Research Network (FCRN). Measurements of energy, water vapour, and carbon dioxide fluxes have been made continuously since August 2003 using the eddy covariance technique, along with ancillary… More

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A carbon (C) and nitrogen (N) cycle-coupled model, CLASS-CTEMN+ was developed by incorporating soil and plant N cycling algorithms in the Canadian Land Surface Scheme (CLASS) and the Canadian Terrestrial Ecosystem Model (CTEM), used in the Canadian Global Climate Model. Key soil and plant N cycling processes incorporated in the model include biological fixation, mineralization,… More

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Understanding seasonal variations of photosynthetic parameters is critical for accurate modeling of carbon dioxide (CO2) uptake by ecosystems. Maximum carboxylation velocity (Vcmax), maximum rate of electron transport (Jmax), leaf respiration in the light (Rday), light-saturated assimilation (Amax) and maximum quantum yield (Φ) were calculated from leaf gas exchange measurements made monthly throughout the year on… More

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Soil carbon dioxide efflux (soil respiration, SR) was measured with eight autochambers at two locations along a wetland to upland slope at Harvard Forest over a 4 year period, 2003–2007. SR was consistently higher in the upland plots than at the wetland margin during the late summer/early fall. Seasonal and diel hystereses with respect to… More

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The carbon sink strength of arbuscular mycorrhizal fungi (AMF) was investigated by comparing the growth dynamics of mycorrhizal and nonmycorrhizal Andropogon gerardii plants over a wide range of equivalent tissue phosphorus : nitrogen (P : N) ratios. Host growth, apparent photosynthesis (Anet), net C gain (Cn) and P and N uptake were evaluated in sequential harvests of mycorrhizal and… More

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