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Re-assessment of plant carbon dynamics at the Duke free-air CO2 enrichment site: interactions of atmospheric [CO2] with nitrogen and water availability over stand development
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International audience. • The potential for elevated [CO2]-induced changes to plant carbon (C) storage, through modifications in plant production and allocation of C among plant pools, is an important source of uncertainty when predicting future forest function. Utilizing 10 yr of data from the Duke free-air CO2 enrichment site, we evaluated the dynamics and distribution of plant C. • Discrepancy between heights measured for this study and previously calculated heights required revision of earlier allometrically based biomass determinations, resulting in higher (up to 50%) estimates of standing biomass and net primary productivity than previous assessments. • Generally, elevated [CO2] caused sustained increases in plant biomass production and in standing C, but did not affect the partitioning of C among plant biomass pools. Spatial variation in net primary productivity and its [CO2]-induced enhancement was controlled primarily by N availability, with the difference between precipitation and potential evapotranspiration explaining most interannual variability. Consequently, [CO2]-induced net primary productivity enhancement ranged from 22 to 30% in different plots and years. • Through quantifying the effects of nutrient and water availability on the forest productivity response to elevated [CO2], we show that net primary productivity enhancement by elevated [CO2] is not uniform, but rather highly dependent on the availability of other growth resources.
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