In the southeastern United States (SE), the conversion of abandoned agricultural land to forests is the dominant feature of land-cover change. However, few attempts have been made to quantify the impact of such conversion on surface temperature. Here, this issue is explored experimentally and analytically in three adjacent ecosystems (a grass-covered old-field, OF, a planted… More

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Estimates of forest net primary production (NPP) demand accurate estimates of root production and turnover. We assessed root turnover with the use of an isotope tracer in two forest free-air carbon dioxide enrichment experiments. Growth at elevated carbon dioxide did not accelerate root turnover in either the pine or the hardwood forest. Turnover of fine… More

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We linked a leaf-level CO2 assimilation model with a model that accounts for light attenuation in the canopy and measurements of sap-flux-based canopy conductance into a new canopy conductance-constrained carbon assimilation (4C-A) model. We estimated canopy CO2 uptake (AnC) at the Duke Forest free-air CO2 enrichment (FACE) study. Rates of AnC estimated from the 4C-A… More

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Forest evapotranspiration (ET) estimates that include scaled sap flux measurements often underestimate eddy covariance (EC)-measured latent heat flux (LE). We investigated potential causes for this bias using 4 years of coupled sap flux and LE measurements from a mature oak-hickory forest in North Carolina, USA. We focused on accuracy in sap flux estimates from heat… More

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Elevated atmospheric carbon dioxide (CO2e) increases soil respiration rates in forest, grassland, agricultural and wetland systems as a result of increased growth, root biomass and enhanced biological activity of soil microorganisms. Less is known about how forest floor fluxes respond to the combined effects of elevated CO2 and nutrient amendments; until now no experiments have… More

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The magnitude of changes in carboxylation capacity in dominant plant species under long-term elevated CO2 exposure (elevated pCa) directly impacts ecosystem CO2 assimilation from the atmosphere. We analyzed field CO2 response curves of 16 C3 species of different plant growth forms in favorable growth conditions in four free-air CO2 enrichment (FACE) experiments in a pine… More

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To investigate whether sun and shade leaves respond differently to CO2 enrichment, we examined photosynthetic light response of sun and shade leaves in canopy sweetgum (Liquidambar styraciflua L.) trees growing at ambient and elevated (ambient + 200 μl l−1) atmospheric CO2 in the Brookhaven National Laboratory/Duke University Free Air CO2 Enrichment (FACE) experiment. The sweetgum… More

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Over two-thirds of terrestrial carbon is stored belowground and a significant amount of atmospheric CO2 is respired by roots and microbes in soils. For this analysis, soil respiration (Rs) data were assembled from 31 AmeriFlux and CarboEurope sites representing deciduous broadleaf, evergreen needleleaf, grasslands, mixed deciduous/evergreen and woodland/savanna ecosystem types. Lowest to highest rates of… More

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