Reassessment of plant carbon dynamics at the Duke Free Air CO₂ Enrichment site

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McCarthy HR, R Oren, KH Johnsen, A Gallet-Budynek, SG Pritchard, CW Cook, SL LaDeau, RB Jackson, AC Finzi. 2009.
Reassessment of plant carbon dynamics at the Duke Free Air CO₂ Enrichment site: interactions of atmospheric [CO₂] with nitrogen and water availability over stand development.
New Phytologist, in press.

Summary

• 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 years of data from the Duke free-air CO₂ enrichment (FACE) 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 estimates of standing biomass and net primary productivity (NPP) than previous assessments (up to 50%).
• On average, elevated [CO₂] caused sustained increases in plant biomass production and standing C, but did not affect partitioning of C among plant biomass pools. Spatial variation in NPP and its [CO₂]-induced enhancement was controlled primarily by N availability, with the difference between precipitation and potential evapotranspiration (P-PET) explaining most inter-annual variability. Consequently, [CO₂]-induced NPP enhancement ranged from 22% to 30% in different plots and years.
• Through quantifying the effects of nutrient and water availability on forest productivity response to elevated [CO₂], we show that NPP enhancement by elevated [CO₂] is not uniform, but rather highly dependent on the availability of other growth resources.

Key words: biomass partitioning, grassland, interannual variability, meta-data synthesis, net primary productivity (NPP), precipitation, temperature.