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

• Published in: The New phytologist Vol. 173; no. 4; pp. 766 - 777
• Main Authors: Hill, P.W, Marshall, C, Williams, G.G, Blum, H, Harmens, H, Jones, D.L, Farrar, J.F
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.01.2007; Blackwell Science; Blackwell Publishing Ltd
• Subjects: biogeochemical cycles; carbon; Carbon - analysis; Carbon - metabolism; carbon cycle; Carbon dioxide; Carbon Dioxide - analysis; Carbon Dioxide - metabolism; carbon dioxide enrichment; carbon partitioning; Carbon sequestration; climate change; cutting; defoliation; Ecosystem; fertilizer application; free air carbon dioxide enrichment (FACE); Grassland soils; grasslands; leaves; Lolium - growth & development; Lolium - metabolism; Lolium perenne; nitrogen; Nitrogen - metabolism; Oxygen Consumption; Photosynthesis; Plant roots; Plants; prediction; Radiocarbon; radionuclides; range management; rhizodeposition; roots; Soil; Soil biology; Soil respiration; Soil solution; Sward; Zea mays - growth & development; Zea mays - metabolism
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/j.1469-8137.2007.01966.x

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.