The fate of photosynthetically‐fixed carbon in Lolium perenne grassland as modified by elevated CO2 and sward management

Hill, P. W.; Marshall, C.; Williams, G. G.; Blum, H.; Harmens, H.; Jones, D. L.; Farrar, J. F.

The fate of photosynthetically‐fixed carbon in Lolium perenne grassland as modified by elevated CO2 and sward management

2007

• Prediction of the impact of climate change requires the response of carbon (C) flow in plant–soil systems to increased CO₂ to be understood. • A mechanism by which grassland C sequestration might be altered was investigated by pulse‐labelling Lolium perenne swards, which had been subject to CO₂ enrichment and two levels of nitrogen (N) fertilization for 10 yr, with ¹⁴CO₂. • Over a 6‐d period 40–80% of the ¹⁴C pulse was exported from mature leaves, 1–2% remained in roots, 2–7% was lost as below‐ground respiration, 0.1% was recovered in soil solution, and 0.2–1.5% in soil. Swards under elevated CO₂ with the lower N supply fixed more ¹⁴C than swards grown in ambient CO₂, exported more fixed ¹⁴C below ground and respired less than their high‐N counterparts. Sward cutting reduced root ¹⁴C, but plants in elevated CO₂ still retained 80% more ¹⁴C below ground than those in ambient CO₂. • The potential for below‐ground C sequestration in grasslands is enhanced under elevated CO₂, but any increase is likely to be small and dependent upon grassland management.

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