Title Canopy CO₂ enrichment permits tracing the fate of recently assimilated carbon in a mature deciduous forest
Author/s Sonja G. Keel, Rolf T. W. Siegwolf and Christian Körner
Year 2006
Journal New Phytologist 172:319–329
Abstract How rapidly newly assimilated carbon (C) is invested into recalcitrant structures of forests, and how closely C pools and fluxes are tied to photosynthesis, is largely unknown. A crane and a purpose-built free-air CO₂ enrichment (FACE) system permitted us to label the canopy of a mature deciduous forest with ¹³C-depleted CO₂ for 4 yr and continuously trace the flow of recent C through the forest without disturbance. Potted C4 grasses in the canopy (‘isometers’) served as a reference for the C-isotope input signal. After four growing seasons, leaves were completely labelled, while newly formed wood (tree rings) still contained 9% old C. Distinct labels were found in fine roots (38%) and sporocarps of mycorrhizal fungi (62%). Soil particles attached to fine roots contained 9% new C, whereas no measurable signal was detected in bulk soil. Soil-air CO₂ consisted of 35% new C, indicating that considerable amounts of assimilates were rapidly returned back to the atmosphere. These data illustrate a relatively slow dilution of old mobile C pools in trees, but a pronounced allocation of very recent assimilates to C pools of short residence times.
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