Fine-root respiration in a loblolly pine (Pinus taeda L.) forest exposed to elevated CO₂ and N fertilization

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Drake, JE, PC Stoy, RB Jackson, EH DeLucia. 2008.
Fine-root respiration in a loblolly pine (Pinus taeda L.) forest exposed to elevated CO₂ and N fertilization.
Plant, Cell and Environment 31: 1663–1672.

Abstract

Forest ecosystems release large amounts of carbon to the atmosphere from fine-root respiration (R_r), but the control of this flux and its temperature sensitivity (Q₁₀) are poorly understood. We attempted to: (1) identify the factors limiting this flux using additions of glucose and an electron transport uncoupler (carbonyl cyanide m-chlorophenylhydrazone); and (2) improve yearly estimates of R_r by directly measuring its Q₁₀ in situ using temperature-controlled cuvettes buried around intact, attached roots. The proximal limits of R_r of loblolly pine (Pinus taeda L.) trees exposed to free-air CO₂ enrichment (FACE) and N fertilization were seasonally variable; enzyme capacity limited R_r in the winter, and a combination of substrate supply and adenylate availability limited R_r in summer months. The limiting factors of R_r were not affected by elevated CO₂ or N fertilization. Elevated CO₂ increased annual stand-level R_r by 34% whereas the combination of elevated CO₂ and N fertilization reduced R_r by 40%. Measurements of in situ R_r with high temporal resolution detected diel patterns that were correlated with canopy photosynthesis with a lag of 1 d or less as measured by eddy covariance, indicating a dynamic link between canopy photosynthesis and root respiration. These results suggest that R_r is coupled to daily canopy photosynthesis and increases with carbon allocation below ground.

Key-words: carbon cycle; Duke FACE; FACTS-1; global climate change; net ecosystem exchange; soil respiration.

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